Automotive ICS DR.
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Automotive Engine Electronics How to Diagnose and Repair the Automotive Computer Control System
by Dr. Robert C. McElroy
Second Revised Edition
Accuracy Publishing, Homestead, Florida
photo by Rick Bernskoetter
Bob McElroy at the wheel of his Hilborn Fuel Injected Corvette at an SCCA autocross. Note video camera attached to windshield.
Published by: Accuracy Publishing Co. Post Office Box 514 Homestead, FL 33035-0514 Corvette Cover Artwork Compliments of: Micrografx Corporation
1511 I
Bob McElroy
Allrights reserved. No part of this book may be used or reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system without prior written permission from the author except in the case of brief quotations embodied in critical reviews and articles. Copyright 1987,1988 by Robert C. McElroy, Ph.D. First Printing 1987 Second Printing 1988, revised Third Printing 1988, revised Printed in the United States of America
Library of Congress Cataloging in Publication Data McElroy, Robert C. Automotive Engine Electronics Understand, Diagnose & Repair: Fuel, Ignition & Computer Control Systems 1. Automotive Electronics--Computers, sensors, etc. 2. Electricity and Electronics--Computers, sensors, etc 3. Diagnosis--Computers, sensors, etc. 4. Mathematics--Computers, sensors, etc I. Title ISBN 0-929603-37-0 S o f t c o v e r
SECTION II -- Driveability Diagnosis
SECTION I -- Sensors & Systems
TOPIC
PAGE
Table of Contents Objective Foreward Introduction About the Author Background of Today's Automobile Electrical & Electronic Terms OHM'S Law Series Circuits Parallel Circuits Series Parallel Circuits Diodes Despikeing and Clamping Diodes Transistors Point Style Ignition Systems HE1 -- High Energy Ignition EST -- Electronic Spark Timing Distributorless Ignition Systems -- CI CCC -- Computer Command Control EFI -- Electronic Fuel Injection PFI -- Port Fuel Injection Transition -- fuel to electronic systems Throttle Position Sensor -- TPS Temperature Sensors -- CTS & MAT Manifold Absolute Pressure -- MAP Electronic Spark Control -- ESC Mass Air Flow Sensor -- MAF Eshaust Gas Recirculation -- EGR Idle Air Control -- IAC Vehicle Speed Sensor -- VSS Evaporative Emission Control -- EEC
3 4 5 6 8 9 11 16 18 20 21 22 24 25 26 29 31 33 35 38 40 43 44 46 47 48 49 50 53 54 55
TOPIC
PAGE
Driveability Diagnosis Philosophy Systems Approach to Diagnosis Electronic Control Module -- ECM ALCL Terminal Circuits Scanner Use Integrator & Block Learn Scanner Error Diagnostic Procedures Digital Multimeter -- DMM Jumper Wires & Connectors Computer Harness Adaptive Tester Diagnostics & ECM Voltage Checks Continuity Tests CHAT Basic Test Procedures CHAT Advanced Testing Procedures Advanced Circuit Testing ECM Codes Open & Closed Loop Fuel Injector Balance Test
SECTION Ill -SELECTED ECM VOLTAGES &WIRE DIAGRAMS
Which can be read with CHAT. Note: CHAT will interface BCM and GMP4 design ECMs. BCM and GMP4 circuits have not been included in this publication. CCC and EFI systems incorporating "edgeboard"connectors were not included.
CHAT is covered by U.S. Patent No. 4,690,475 and is available from Diagnostic Products Co. P.O. Box 1136, Homestead, Fl. 33090 Diagnostic Products Co.is the Electronics Subsidiary of Spectra Investments Ltd. Inc.
Objectives of this manual: Provide a comprehensive general explanation for electronically 1. spark controlled and fuel injected engines manufactured by GM. 2.
Provide specific information for the use of ALCL "scan" tools.
3.
Provide specific information for the use of "CHAT' the Computer Harness Adaptive Tester.
4.
Provide specific information for the use of CHAT to perform voltage and continuity testing for all wires and circuits interfacing the ECM.
This manual has been prepared for: 1.
Professional Technicians in the field of automotive repair.
2.
Students of Automotive Technology.
3.
Automotive Enthusiasts who wish to know more about contemporary automotive engine electronics.
This manual has been prepared with a "systems" approach: 1.
Diagnosis and repair must be performed in a step by step method, to ensure that you "isolate" the problem, and not simply replace what seems to be wrong.
2.
Automotive systems are broken down so that you can see how they are intended to work in a conceptual method. When you understand the general concept you will be able to apply your understanding to systems and components which differ from those included in this manual.
This manual is not intended to replace applicable service manuals pertaining to the service of any automobile. This manual is intended to complement service manuals specificallyprepared by the vehicle manufacturer.
In order to understand the complex nature of today's automobile we must be able to speak and understand the language used to describe these vehicles. You may be reluctant to want to learn anything, but you have made it this far by purchasing this book. A book which you can use and learn new technology from. A book written to help you each and every day on the job.
Always try and do the job right the first time even if it takes a few extra minutes. One good example would be a water pump. If it leaks then you will probably have to do the whole job over and I don't know of anyone who wants to redo a water pump. The same sort of thinking applies to this new technology. If the car still has a driveability problem then it is going to be a comeback and rechecks eat your earnings.
Actually, when you start to dig into this material it will be fun and interesting. The trick is to just take your time and master these basic terms and concepts. One thing that you really need to do is understand how these things work, at least on a simple level. This book will approach everything on a simple level and use this basic principle of understanding to build upon. Some of the things which we will look at in the beginning will seem too simple to really work with. However, I have seen too many repairs done incorrectly. When you really analyze what you are doing the bottom line really must be to get the car fixed. Hopefully, this will happen the first time or else you will have a recheck to perform. Rechecks mean that you will not be making money on the next car waiting for you. Therefore, the fewer rechecks the more money you ought to make. That seems simple enough, doesn't it?
NO RECHECKS
This book has been prepared with the objective of presenting basic concepts which apply to the modern automobile which uses a small computer or ECM to control fuel delivery to the engine. In order to understand how this system functions, you will be presented the basic concepts relating to how air and fuel management is accomplished. If you know and understand the relationships between the sensor inputs and computer outputs you will be able to diagnose problems which occur with the modern automobile. No one book can be expected to provide all information which can apply to all situations. However, the information provided will be of value when you must diagnose and repair these vehicles.
Your use of a definite method of analysis will increase your productivity and reduce the number of comebacks and your number of rechecks. This increase in productivity will make you a better technician which should also correspond to an increase in your paycheck. In order that you understand how this system works we will first investigate the ignition system. Understanding of today's ignition systems is 100%essential. Proper fuel delivery to the engine is based upon this input signal and without it the vehicle will not run due to loss of both spark and fuel delivery.
As you gain experience with computer equipped cars and trucks you will find that they do perform and react in a predictable way. There are certain things which you must know and understand. Some things must work or the vehicle simply will not run. These facts will be covered so that you will be able to NO WRENCHES ON quickly and accurately determine if THE RED TERMINAL these necessary inputs are present. Use of a definite strategy will mean that your diagnosis is done quickly and in a logical Always remove the ground cable first. If you procedure.
accidentally hit some sheet metal you will not risk blowing up the battery.
I believe that many technicians do not have a good understanding of how ignition systems operate. Therefore, we will study a conventional point-type ignition first. If you know and understand how this system works you will not have any difficulty with electronic systems. More cars are being designed each year without distributors. As you progress through your study of this book, you will clearly come to understand why a distributor is not needed. As you learn how these systems operate and how other inputs can provide the same necessary signal you will be able to figure out and troubleshoot systems which you have not personally worked on yet. As you study this manual and compare its information to the cars which you work with daily you will become a better technician. Additional education at your local technical school or community college will also help you to be more professional in your duties. If you are not already certified by ASE, you are encouraged to participate. ASE certification is a highly desirable goal and those technicians who wear the ASE patch take pride in their accomplishment. You make your living as a technician. Vehicles which you work on daily are highly complex and the more you know about these vehicles the better off you are. Your need for technical literature and education have never been greater. You demonstrate your professionalism when you wear the ASE certification patch.
YOUR TECHNICAL JOB
THE MORE YOU KNOW THE MORE THINGS YOU CAN FIX
FASTER & MORE RELIABLE
EVERYONE BENEFITS FROM TECHNICIAN CERTIFICATION
SUPPORT IT!
I walked into my local Chevrolet dealer and asked for a job as a junior mechanic and grease monkey during my summer break from college in 1969. That did not last long; soon I was tearing apart engines and trying to figure out how to get them running again. The more things which I could fix, the more work I got in the shop.
equipment. When you know what you are supposed to do, and you do it well, then you can really enjoy what and how you do things. I would hope that you personally feel that way about your occupation ...if you do not then I hope that this book will help you to gain this type of confidence.
I drove my first race car in 1965. It was while I was a senior in high school in State College, Pennsylvania. We even raced in the winter. I remember trying to run over a snowbank during one event while racing on the icy surface. This interest in racing has probably been the key to why I have always kept a strong interest in automotives.
For a period of three years I was in the position of resident engine instructor, at one of the 31 GM training centers in operation at that time, after having been recruited by General Motors in 1983 . In Detroit we would be given product information which would be used to conduct classes about new engine systems and their operation for dealership technicians who would attend our classes. All this new information was great, but this information had to be passed on to the fellows and an occasional lady who actually "turns a wrench" to make a living. It really was a lot of fun.
Over the years I have raced many different types ofvehicles including the likes of jeep, ferrari, pantera, vega, corvair, mustang, police cars, and my favorite, the corvette. Those police cars came from when I taught High Performance Driving to police officers at the Texas Transpor- Additional qualifications to be your autation Institute. thor to write this book besides my experience with GM, racing, and having been I have always felt that if you are going to a "Chevrolet Certified Technician" win on the track then you must field the would include formal college education best car. Even if you happen to be the background of a BS, MA, and finally a best driver around, if your machine is not Ph.D. in industrial education from Texas set up properly then you cannot win. I A&M University. In 1987 I was one of have never gone to an event with the idea 375 people inducted into the Automoto lose. Of course I don't always win and bile Hall of Fame in Midland, Michigan I do get beat sometimes, but I don't lose. as an "ASIA/ASE 'World Class' TechniIt really is a state of mind where you feel cian" for holding all 16 ASE area certificonfident about your ability and your cations.
Way back in the old days, pre-computer cars that is, we basically concerned ourselves with three types of problems: 1) fuel, 2) ignition, or 3) mechanical. However, today there is an additional 4) electronic problem area which really gives technicians a tough time. This latest addition to our problems is the most difficult to understand. You simply cannot take apart a transistor with a 9/16" or lOmm wrench. Since you cannot easily disassemble this electronic stuff it means that you will probably have to learn about these things either on your own or in a class somewhere. This book will help you understand how automotive electronics work and this book will help you fix today's electronically complex cars. When cars were simple it was not too difficult to figure out which area theproblem was in and then it could be attacked. If there was a question about ignition, then did spark come out of the plug wire? If not then points were pretty easy to fix. I remember a 1970 LT-1 corvette at the dealership, the ticket said "won't run". I found the car, it would crank but not start. I popped off a plug wire and hung it on top of the air cleaner wingnut; crank engine again and no spark but the 12 volt test light says power to the coil and a good
ground. Hmmm ...the points must be locked up. Off with the chrome shroud, remember this is a corvette, off with the distributor cap ...what the .... So much for my first introduction to transistorized ignition. Today's cars may affect you the same way. There is no denying that cars are much more complex than ever before and there is no alternative to understanding how they operate. Because of Federal regulations for improved fuel and emission characteristics of our vehicles it became necessary to develop more sophisticated engine control systems to meet these new standards. Many of you reading this book look favorably on the past but you know that "simple" cars are no longer built; also you know that the carburetor is in fact only a "calibrated leak" which will not do the job today. Microprocessors are the heart of the computer or Electronic Control Module, ECM for short. Microprocessors get information from many sensors placed all over the vehicle. Microprocessors take this information and run it through the operational program recorded permanently inside the machine found on
10 ROMS and PROMS. After all this analysis is done then some sort of output will come from the ECM such as when to inject fuel and how long the injectors are to be held open.
This entire information transmission process at first seems almost impossible to figure out. However, this is not the case. There are some very logical relationships which do exist and you as a professional technician already know the basic principles of engine operation. We will take these things which you are already familiar with and use them as the basis for all the new systems. New systems may be new but they accomplish the same sort of things as the old systems. Whether or not new systems are better is something which most mechanics and technicians have personal opinions about ...j ust ask one! Let's face it, there is no alternative ...you have to know how the new systems operate if we are going to be successful in this occupation. How did you learn to be a technician in the first place? Were you taught by other mechanics or did you attend a technical training program? I expect that you actually have some of both. You have already invested heavily in your education; some people would call this the "School of Hard Knocks." You have invested thousands of dollars in your tool box. Every time the tool truck comes by you can think of additional tools which will make you more productive. Tools are an investment in your future, there is no other alternative there.
When you finish reading this book you will find it to be an excellent reference. Others will want to use this book. As with any tool you will need to have it available at times. You know who borrows your tools and this book is no exception. A saying that I have seen on one master technician's toolbox is "I would rather loan you my dog than my tools. The dog always comes home." It applies to this book too.
IF YOU WANT TO FIRE TWO SPARK PLUGS AT THE SAME TIME, HERE IS HOW IT'S DONE.
First off let's look at wire. With wire we can "pipe" electricity to every device in the car which needs energy to operate. Most wires in the car are made from copper. Some wires in the body harness of the car are aluminum but these are rare, and require special wire repair techniques. Copper is a very good conductor. A conductor is a material which allows electrons to flow through it easily. If you are going to keep the electrons in the wire you must cover the wire with a tough material which will not let the electrons INSULATION get out of the wire. This material is called an insulator. Most wires are covered with an insulator, which is generally a type of plastic. Wires carry electrons. Electrical pressure is Enough electrons moving will create an electrical current. How many electrons you need to perform a job depends on the load. A crank or starting motor requires a large electric cable cLming right-from the battery, while a dome light needs only a small wire to work effectively. The electrical pressure to both the crank motor and dome light are the same. Electrical Pressure is called VOLTAGE. Both items get the same voltage or pressure coming from the battery because
called voltage. Quantity of electrons is measured in amps.
I
12 wires conduct the electrons to each item. If the battery has a 12 volt potential difference between the B + (red) and B(black) terminals at the battery and we connect a wire to the B + and a wire to the B- and then go to the end of each wire and place a voltmeter between them we should have 12volts shown on the meter. If both the crank motor and the dome light get the same electrical pressure then why the different size of electrical wires and cables? Both devices get 12 volts. The difference is how much work each device must do. That large cable to the crank motor will allow many more electrons to move than the small wire to the dome light. The quantity or amount of electrons flowing is called AMPS.
SY MBOL
-
-
BAllERY VOLTAGE (PRESSURE) IS CARRIED BY WIRES
CRANK MOTOR
-
I
-
DOME LIGHT AND CRANK MOTOR GET 12 VOLTS CRANK MOTOR USES MORE AMPS THAN DOME LIGHT CRANK MOTOR USES LARGE CABLE DOME LIGHT USES A WIRE
INSUlATION
WIRE
A LARGE WIRE WILL CARRY MQRE AMPS REMEMBER -- TjYE SAME V ' LTAG€ IS AFTLIED TO B U M WRES!
If I had two cars, one with a 4 cylinder engine breathing through a lbbl carburetor and the other car had tunnel ram and two Holley Double Pumpers ...then which one will use the most fuel? The tunnel ram will use the most fuel because it needs that fuel to do its job properly, just like the crank motor will need a lot of amps to do its job properly. If both our cars use the same type of pump gas, then in order to make more horsepower we must deliver more fuel to the engine. Therefore we invest in the big 110 gallon per hour electric fuel pump and use a I/ 2" or larger fuel line between the fuel tank and tunnel ram.
If a fuel fitting leaks our car will not run the way it is supposed to. If an electrical wire starts to corrode it will not conduct current properly. If a fuel line breaks the car will not run. If an electrical wire is cut the component will not work. If gasoline spills and is ignited your car may be destroyed. If an electrical wire is shorted to ground the electrical system and possibly the car might burn up.
SHORT CIRCUIT BRACKET HAS WORN THROUGH THE INSULATION ON THIS WIRE CAUSING A SHORT TO GROUND
Current, when flowing inside a good wire, can be considered to have no resistance to its flow. Wires act as a pipeline of energy to the item or component we need to run. When current cannot flow easily to a component, resistance has been added to our circuit.
DO NOT USE CRIMP CONNECTORS ON TODAY'S CAR. CRIMP CONNECTORS PROMOTE CORROSIONWHC IH CREATES RESISTANCEAND HEAT IN THE WIRE.
Resistance in a wire is bad. It generates heat inside the wire and it means that not enough current will get to the component on the end of the wire. The component may not work properly because it does not have enough current to perform within its operating limits. This reduction in current may cause the component to fail. Resistance in a component means that the item will perform work for us. Imagine you are holding a fire hose with water spraying into the air. If you aimed this hose at the side of a mountain you would start to wash away the mountain and the stream of water would be doing work for Crimp connectors used for repair on this late you. The mountain becomes resistance model T Bird will create electrical problems for the rest of this car's life. to the flow of water. Work is performed as you wash away the mountain. Each electrical item which performs work in the car has some resistance. Resistance means that current cannot simply flow right through the item to ground. The current must do something which we want it to do in order for the current to get to ground. This internal electrical activity or flow will operate each electrical component in the car for US.
Some components offer static resistance to current flow and some items have dynamic resistance to current flow. If you have ever taken apart a solenoid coil you have found that there are many feet of wire in the coil. The length of wire and the size of wire cause resistance inside the coil. This is an example of a static resistance.
MAGNETIC FIELD
Light bulbs and crank motors have dynamic resistance to the flow of current. When these items are working current cannot get across them fast enough. As the armature moves past the brushes in the crank motor, current flow is not continuous because current is directed to different parts of the armature winding because of the contact point placement under the brush. A crank motor which is locked up can have a very high current draw.
CRANK MOTOR
COMMUTATOR
MAGNETIC FIELD
A mathematical relationship exists between volts, amps and ohms in any electrical circuit. George Simon Ohm discovered the relationship between these factors and named the formula after himself, hence the name Ohm's Law.
Mr. Ohm found that volts or pressure in a circuit will move a quantity of electrons or amps through a defined resistance or ohms. This relationship means that if you know any two of the three factors then it is possible to determine the third item mathematically. Although many technicians have difficulty in learning Ohm's Law it is a very important relationship which definitely needs to be mastered. Specifically, when you know and can even visualize (yes actually see in your mind) how these three aspects of electrical flow work together then you will be in a much better position to fin the modern car which uses a microcomputer to control engine operation. The Electronic Control Module or ECM does everything electrically. Voltage is the language of the ECM. Voltage is pressure. The ECM will control electrical pressure to get things done. Just like you flip a switch to turn the lights on, the computer will controlvoltage to a transistor (functioning as an electrical switch) in
Ohm's Law Terms: E = Voltage I = Amps R = Resistance Ohm's Law: T
I
- -E - R
E = IXR
order to activate an output. For example, the air conditioning compressor clutch which would be disabled during wide open throttle to allow maximum acceleration.
In Ohm's Law: Amps x Ohms Volts
Ohm's Law will help you fix problem cars. The ECM is designed to handle only 1/2 amp on most circuits. This means that the relays and solenoids must have 20 ohm or greater resistance or you will blow the ECM. Only "protected" circuits can handle currents greater than 1/2 amp, an example being the fuel injector solenoid but this circuit is only pulsed in milliseconds (thousands of a second). 12VOLT
RESISTANCE SYMBOL
12 A M P
1 OHM
12VOLT
OMEGA SIGN IS USED TO SHOW OHMS
1 A M P
12 OHM
12VOLT
OHMS
A M P
24 OHM
In a series circuit all the components or devices are hooked up end-to-end. This arrangement means that all the current (amps) in the circuit is the same through each componenet used in the circuit.
BLOWER MOTOR RESISTOR BLOCK SERIES CIRCUIT DIAGRAM
Current flow in a series circuit is like a water hose. All the water passes through the hose from end to end. In a series circuit the same amount of current passes through each component. SERIES CIRCUIT LAWS: 1. In a series circuit the current flowing in the circuit is the same at all points in the circuit. 2. Total resistance of the series circuit is the total of all individual resistances present in the the circuit.
3. The sum of all voltage drops, across each resistance, in a series circuit equals the applied or source voltage.
w MOTOR
Question: In a series circuit with three resistors, calculate the total resistance (R T), and calculate the current flow using Ohm's Law. Step 1 -- list given values
I
12 VOLT
wd
H
I
-- determine
Step 2
total resistance R T
RT=R1 +R2+R3 RT=2Q+4n+6Q=12n
Step 3
-- apply Ohm's Law to determine amp flow
R 3
I
AAAII V I = -E = 12 -= R 12 fl
lamp
Question -- Now that you know the amount of current flowing calculate the voltage drop across each resistor using Ohm's Law.
E= IX R
Ohms' Law equation
to determine voltaqe drop across each resistor multiply amp flow times individual resistor values E r l = 1 ~ =~ I1ampx2R = 2 w I t s Er2 = I X R ~= 1 ampx4R = 4volts Er3 = IxR3 = 1 ampx6R = 6volts total voltage drop = Erl + Et2 + Er3 = 2 + 4 + 6 = 12 volts
.
A parallel circuit has two or more branches in which all the positive terminals are connected to a common point and all the negative terminals connected to a common point. Therefore, the same voltage is applied across each component.
INSTRUMENT PANEL LIGHTING PARALLEL CIRCUIT DIAGRAM
Parallel Circuit Laws : 1. In a parallel circuit, the voltage is the same across each branch. 2. Total current in the circuit is the sum of the current flow in each branch.
I
RHEOSTAT
3. Total resistance of the parallel circuit is always less than the smallest resistive branch.
Maximum Panel Brightness Set rheostat for O ohm. 12 u. is applied across each bulb. E Ohm's Law equation I =
w
I = elr I = 12vl2Oohm 1 .6 amp {per bulb) Amps total = amps per bulb x number of bulbs lt=.6ax5=3amp
Series - parallel circuits combine aspects of both series and parallel circuits. In the series part of the circuit all the current passes through one circuit component. In the parallel circuit there are multiple paths for the current to pass through.
INSTRUMENT PANEL LIGHTING PARALLEL CIRCUIT DIAGRAM
In this example the rheostat is the series load and the bulbs are the parallel load. To calculate current (amps) first determine the resistance of the parallel components. Add the parallel resistance to the series resistance in order to determine total resistance. Use Ohm's Law in order to determine amp flow in this circuit. Voltage drop across series and parallel segments can be determined by Ohm's Law by multiplying amps times resistance for the series segment.
Parallel resistance = 20 ohm / 5 = 4 ohm Series resistance = 8 ohm Total resistance = 4 8 = 12 ohm Amp=E/I = 12v/12ohm=lamp Voltage drop of series, E = I x R, 1 x 8 = 8V Voltage drop of parallel, 1a x 4 ohm = 4 volt Amp flow through each bulb I = E/R I = 4 v / 2 0 o h m = .2amp Total amp flow through bulbs .2 amp x 5 bulbs = 1 amp
+
F U
5 E
HEADLIGHT RHEOSTAT
DIODES Diodes are devices which will allow electricity to pass through in only one direction. DIODES are simply a ONE WAY VALVE. They allow current to pass through in one direction and if the current tries to reverse direction, then the diode will block current flow. Alternators use nine diodes. Six diodes are in the rectifier bridge and three in the diode trio. These diodes turn the spinning action of the alternator and its alternating current (AC) into direct current (DC). If any one of these diodes fail, performance of the charging system will be greatly affected.
DIODE ELECTRICAL SYMBOL
DIODE CURRENT FLOW
LIGHT EMITTING DIODES Light Emitting Diodes or LED's are used frequently in many automotive applications. They are built like a regular diode only they are designed to produce light . Whereas a regular diode made from silicon will require about .6v to turn on and pass current, the LED needs 1.5to 2 . 2 in ~ most applications. LED's are just like regular diodes because they will not pass current that wants to go against it.
LIGHT EMITTING DIODE
ALTERNATOR OPERATION THROUGH EACH PHASE
X X X X X X
TRACE CURRENT FLOW THROUGH DIODE BRIDGE IN EACH DIAGRAM
WOUND STATOR
SINCE ALL THE CiJRRENT MUST PASS THRGUGH THE CENTER CONNECTION LESS OUTPUT RESULTS
I
CONVENTWNAL
Y 5TATOR
Diodes are also used to "bridge" solenoids. Review of the information on ignition systems shows in detail how the primary coil builds up a strong electrical field in the secondary coil, enough to fire the spark plug when the primary coil is turned off. This condition is normal for the many electrical coils and solenoids in the car. Of special concern are the coils controlled by the ECM. Diodes are placed across many coils. They are installed in a "reverse bias" position to block B + and therefore the current passes through the coil. When B + is turned off the magnetic field of the coil collapses inducing current flow in the coil. This current then passes through the diode, since this current is headed in the same direction as the diode arrow, which was previously blocking B+ and thus this current flow induced by the electric field of the coil is allowed to "collapse upon itself'. A spark is not produced and the delicate ECM is protected against damage. Even small coils, found in simple relays, can produce over 100volts when they are turned off. Large air conditioning clutch coils can produce 60v to 130v with much greater amp flow. Higher voltages are produced with quicker clutch return times. You will see this despiking diode connected to and taped over, on the electrical plug attaching to the ac compressor.
A / C COMPRESSOR CLAMPING DIODE
CURRENT CONTINUES TO FLOW THROUGH THE CLAMPING DIODE UNTIL THE COMPRESSOR FIELD COLLAPSES UPON ITSELF
Transistors are simple little devices when you understand how they do in fact work. The best way to understand them is to first look at a simple old light switch on the wall. You flip the switch up and the light goes on. You flip it down and the light goes off. Now if I tell you that the transistor works exactly the same way as the light switch, only electrically, and that instead of manually pushing the switch you need only send a little voltage to it in order to turn the light on, then we've almost got it licked.
N P N TRANSISTOR
Look at the diagram on the NPN transistor. Notice that the main current path is from top to bottom. Coming in from the side is the small current path necessary to turn on the large current flow. This means that you could use a very small and light duty switch to turn on a high current requirement accessory. It only takes .6v to turn on the average transistor.
R
Transistors function as switches and they can function as a flow control valve. Now that we have the transistor turned on, if we want to let more current flow through it, top to bottom, then we simply apply more voltage to the base. When the transistor is at "saturation" it is allowing all the current through it is designed for. Drive it beyond saturation and it will be destroyed. 9,000 rpm with your street motor won't work. However, a little voltage change on that base lead will be just like your foot on the accelerator.
NPN TRANSISTOR Nclativc POSI~~VC Nejativc Semiconductor nternal cm~tructim
P N P TRANSISTOR
F L
PNP TRWSTOR
Semiconductor internalconstruction
A SMALL CURRENT IN THE BASE LEG WILL TURN THE
-
I
POINT SET
------------------POINT TYPE I G N I T I O N SYSTEM
Point type ignition systems were the standard ignition method for cars by winning out over early magneto systems. If you understand how the point system works you will be able to service millions of different cars, but they all work the same, even if the actual components are different. Refer t o the picture and find the 12 volt source. Let's follow our current through the system and see what actually goes on. First the current flows through the Primary Ignition Coil, which is composed of large diameter wires to allow lots of amps through. If you were to check a primary ignition coil with an ohmmeter you will probably find about one ohm of resistance. One ohm means that there is very
little resistance to current flow, but when the current does flow it sets up a large electromagnetic field around the coil (see page 13). This electromagnetic field is essential to the operation of the coil because it will induce current into the Secondary Ignition Coil later on, but for now this magnetic field is just building up in strength. Now that the current has passed through the primary coil it heads onto the Contact Point assembly. In fact it goes all the way to the Top contact point, as shown in the diagram. The top contact point always will be hot. If you took a voltmeter and touched it to the top point you would see 12 volts. If you have ever installed or held a set of
points you know that there is a spiral spring used to bring the contact points together. In order to separate the points the rotor lobes must be positioned, in relation to the rubbing block on the point locator arm, so that the points will alternately open and close as the rotor turns. Since the top point is always electrically hot, whenever the points come together current will flow across to the bottom point and thus to ground completing the circuit. Many amps will then flow through the primary ignition coil rapidly buildingtheelectromagneticfield around both primary and secondary coils. Since the rotor is generally driven by the camshaft it will continue to turn. A lobe of the rotor will begin to rise, eventually pushing the top point away from the bottom point. At that time the primary coil will be turned off since current can no longer flow through the primary coil.
27 the process of collapsing they cut across the secondary ignition coil winding and begin to induce electrical pressure in this coil. The secondary coil can have 6,000 to 14,000ohms resistance which means that it is a very long coil of wire and the collapse of the electromagentic field will cut across a lot of wire length.
This is exactly what happens and the electrical pressure built up in the secondary coil becomes so great that it will eventually jump a large air gap. The air gap of course will be on our spark plug, igniting the engine air fuel mixture at just the right time to make for good power and driveability. CAPACITOR
This is a good time to look at the "electrical shock absorber" or capacitor. Let's go back to the primary ingition coil for a minute and look at what's happening. When the contact points close current passes through the primary coil and on through the contact point set to ground. When the points are pushed apart the circuit is broken and the electromagnetic field will start to collapse inducing electrical pressure strong enough in the secondary coil to fire the spark plug. What about the primary coil...it will have an induction also....
The Electromagnetic Field which was built up around both the primary and secondary coil will start to collapse. This field is made up of "magnetic force lines" which will start to fall back upon the primary coil. These lines of magnetic force will attempt to push current through the primary coil to keep the current flowing...sort of like lifting your foot off the gas while driving at 50 mph, the car will continue to coast since you Imagine the points just opening, many have already built up speed and momen- electrons will be hurriedly moving along; tum. just like that car at 50 mph. Your car might "stop on a dime" but I would guess These magnetic lines of force try to do the that a lot of skid marks would result if you same thing only electrically. However, in locked up the brakes all the way to a
28 "dead stop," then you would need to go buy some new tires because of the flat spots. If you haven't tried this just ask some of the guys at your service facility; I'm sure that there is someone there who has destroyed some perfectly good tires by locking up the brakes. Of course the best way to stop is to use the brakes, that's why a car has brakes.
Electricity flowing in the coil needs a way to stop without "crashing out." Such is the job of the capacitor, it provides a "run off area" or another path for this electricity to go. Have you ever been to the mountains and noticed "truck run offs" which are large sand pits that 18wheelers can head into if their brakes quit while going downhill. A capacitor is exactly the same thing, an electrical run off with no escape other than go back out the way the current originally came in. When the points close many electrons will start moving. When the points open these electrons will build up tremendous pressure on the top point as they all try to keep on moving. If we add a capacitor then the electrons will electrically take the capacitor for ground and head off into the capacitor. A capacitor is a "false ground" in this application because the electrons cannot actually get to ground they only think that they can. The capacitor will use a large internal surface area or "plate" wrapped up inside it, positioned very close to another "plate" which is attached to ground. Thus the electrons think that they can get to ground by going through the capacitor. As more and more electrons enter the
capacitor it will build up electrical pressure and start to build up resistance to the other electrons which are also headed into the capacitor. When the electrical pressure gets higher than that of electrons trying to get in, then electrons will flow back out of the capacitor. Thus the similarity to the shock absorber give-andtake. If you have ever wondered about those bumpy little lines on an ignition oscilloscope...well now you know. Those funny lines are the electrons bouncing back and forth because of the capacitor. If the capacitor is bad then you will burn out the points because instead of just sparking the spark plug you will also spark the points and they will simply burn UP.
Capacitors are used in many applications. They reduce alternator hum in the radio. They are used any place that electrical pressure (voltage) fluctuates and you need to smooth things out. Nothing is supposed to go through them, unless it's been blown out. They normally seem to work quietly and forever...until it quits and something burns up.
4 CYLINDER MAGNET IC TRANSISToR
12 VOLT
4
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PICKUP C O I L
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HE I HIGH ENERGY I G N I T I O N SYSTEM
Now that we know how a set of points work we can move into HE1 which is really a logical progression of ideas and technology. In review, we know that the points close allowing the primary coil to build up an electromagentic field which collapses when the points open inducing electrical pressure (voltage) into the secondary coil which causes the spark of the spark plug. HE1 works the same except that a transistor is used instead of points. Since the transistor is electronic it won't burn up like a set of points. I didn't say it wouldn't burn up, I'm sure that you can destroy anything but that's not the point. Anyway, the idea is that a transis-
tor will not need as much attention or maintenance as the points. Now all we have to do is turn the transistor off and on and everything will be great. If you haven't read the section on transistors stop here and go do it. This book is designed with the KISS method, meaning Keep It Simple Stupid and your author thinks that you better understand how this mess workswith the easy stuff first. I didn't say-I was easy, I said that it was going to be explained simply. If you do not understand how point ignition systems work or you do not understand how the transistor works, then do yourself a favor and go back to these systems now for review. HE1 can be simple but it will only be simple if
30 you understand the basics. Have you ever seen a 440-T4 transmission pulled all the way down? It will cover every workbench in the shop. I can overhaul a turbo 400 but I would not even want to think about the 440-T4. What does this have to do with HEI? As a wise man once said (he was with the World of Outlaws, the sprint L4 Terminal HE1 Module car association) "if you're going to run with the 'big boys' you better come prepared." Moral of the story... don't try to Therefore: 4 star = 4 cylinder, 6 star = 6 fix something you don't understand and cylinder, or 8 star = 8 cylinder. you can't fix something that's not broke. If this explanation makes sense to you In order to make the HE1 transistor work then you will be well prepared to deal all we need do is to provide it with a small with any electronic ignition system. voltage to turn the primary coil on. This Making the primary coil work will be the small voltage comes from the Magnetic function of a power transistor. Making Pickup assembly which now replaces the the power transistor work will be a funcrotor of our point ignition system. Have tion of some sensor. The pickup sensor you ever noticed how magnets react to may be magnetic, hall effect, or optical. each other? Either you cannot pull them However there must be some sort of apart or you cannot push them together, pickup mechanism. Once you have the no matter how hard you try. general electronic ignition system figured out you should be able to diagnose Now we've got HE1 licked. Put a star most problems by referring to specific magnet on the distributor shaft and put a information provided by the manufacmagnetic ring outside it. When the dis- turer of the subject ignition system. tributor shaft spins the magnets will produce an alternating current. Take this Remember, what we are dealing with in current and pass it through a diode and this book are general concepts which will now we have pulsating DC because half help you diagnose problems. This type of the original AC is blocked. Now add the information is universal and therefore it Zener diode and we have a nice square can be applied each and every day to your wave produced which will make that work. You have special tools in your tool transistor work just like a set of points. box which you seldom use. This information is valuable each and every day as you To get the HE1 right for your engine the approach new problems. To fii the car is magnetic pickup needs to have the same one thing. To understand what was number of star points as the number of wrong with it and then be able to fi it is cylinders in your particular engine. much more difficult.
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--------REFERENCE
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EST
5 VOLT BYPhSS
HIGH ENERGY I G N I T I O N SYSTEM WITH ELECTRONIC SPBRK TIMING
With advent of the on board computer or ECM, mechanical and vacuum advance could be eliminated. The computer could simply look at its sensor values and determine what it wanted to do with ignition timing.
5 volts to energize the bypass coil. The bypass coil pulls the relay control arm over to the Electronic Spark Timing contact and this signal is then fed to the power transistor.
In order to get this system to work we simply change the routing of the signal from the original HEI. When the engine starts the HE1 works like normal, as we have looked at, with the magnetic signal going to the transistor to operate the primary ignition coil. When the engine reaches 500 rpm the computer will apply
Inside the ECM there is a signal linking between reference and EST. Hence, when the reference signal is received the ECM knows to send out an EST signal. If reference is lost the engine will stop running. Why? Send no signal to the ECM and it will think that the engine is not running so no signal will be sent out to the power transistor.
Engine Starts on Base Timing ECM EST Rclcrcncc
-)
Bypus
During crank and until 500 rpm the engine runs on Base Timing, just like standard HEI.
Ground h
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Enginc Runninj With EST ECM t EST Rcfcrcncc -) Bypass
?=
Ground
At 500 rpm the ECM sends 5 volts down the bypass. This switches timing control to the ECM and Electronic Spark Timing is engaged.
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During the 1982 model year GM ignition modules for this type of ignition system began incorporating an internal resistor at the end of the EST contact. This was done so that the ECM could send a circuit checking voltage down the wire before EST was engaged. Otherwise, if the EST circuit was open or shorted to ground the engine would stall when EST was cycled on by the ECM. This circuit check is now performed before EST is engaged. Before this feature became standard the engine would stall when EST was engaged. This start and stall cycle would happen repeatedly. On carburetor equipped cars
you could disconnect the 4 wire connector of the distributor and the car would continue to run because then the 5 volt bypass signal would not be applied to the module. On EFI' and PFI cars if you jumper together the A to B connectors in the ALDLyou should notice a change in rpm to show you that the EST is working. GM diagnostics say to do this at 2,000 rpm but you can notice the rpm difference at idle. Do not drive the car with A to B jumpered together, you can burn the car up. For more on this subject refer to the scanner and how it affects the car.
You really don't need a distributor, you only think that you need it. Let's think about this a minute and maybe it will not seem quite so bad. At first it really bothered me that the distributor was gone but then I realized that it wasn't any good to me and that if it was eliminated then I would have one less thing to take up space on top of the engine.
For many six cylinder engines a 3 vaned rotor is mounted on the back side of the harmonic balancer. When these vanes pass through the Hall Effect sensor a square wave signal is produced. Each vane is dedicated to only one coil pack which will fire two spark plugs at one time. The cylinder on compression and the cylinder on exhaust. SWARE WAVE PRODUCED BY W EFFECT SYSTEM
As for the basic idea, well let's start with the distributor shaft. It is powered by the camshaft. With the pole piece creating the control signal for power transistor of the HE1 module. If a Hall effect sensor were hooked to the harmonic balancer then the spinning crankshaft would give \ FIXED POSITION us the best indication of exactly where the MAGNET crank is. However, since the crank goes around twice for every revolution of the camshaft we must fire two cylinders at the same time in order to get the engine working properly, which is how it works. This start up signal could also come off a Hall effect sensor mounted on the timing The only trick is to get the coils started off gear since it would also identify where to in the right sequence and then the elec- start and then the crank Hall effect would tronics will keep everything working take over for crank position. right. This initial signal can come from several places such as using a double Hall These crank generated signals provide effect sensor on the balancer with one the same information to the ECM as it having only one vane to electronically would receive from the magnetic pickup signal the start up sequence and then the in a standard HE1 only now we do not regular vaned sensor can provide the need the distributor to generate these control signal to operate the coil packs. signals.
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c31
COMPUTER CONTROLLED COIL IGNITION
3 VANES ARE MOUNTED O N THE BACK SIDE OF THE BALANCER
EACH VANE CONTROLS ONE COIL
SQUflRE WflUE PRODUCED BY HflLL EFFECT SENSOR I S SENT TO THE ECN I S ENGINE REFERENCE SIGNIL
Federally mandated Corporate Average Fuel Economy or CAFE standards set minimum emission requirements and fuel economy requirements. GM determined that the traditional carburetor system could no longer get the job done of controlling the air / fuel mixture. Computer Command Control or simply CCC could adequately meet these legal standards. CCC put a computer in the CCC Carburetor is an expensive and comaverage automobile.
plex device. Special training and special tools are necessary before making any A small on-board microcomputer was adjustments to this type of carburetor.
selected to perform the task of keeping watch on the air / fuel mixture. Specifically, this microcomputer called an Electronic Control Module or simply, ECM is A regular carburetor (no wires coming intended to watch what happens in the exhaust pipe and use this reading to out of it) will have metering jets or orifice to allow fuel to pass through in order to meter fuel into the engine. get into the airstream going into the. The basic principle is straightforward. engine. CCC carburetors can control Monitor engine exhaust in order to con- fuel flow through the jets. trol fuel delivery. This is the operational principle behind every automobile manufacturer's system relating to air / fuel control in order to meet applicable fuel and emission standards. In order to make this control system work it seems that just about everything under the hood and on the engine had some sort of computer wire coming out of it. Making a carburetor into a precision metering device seemed like a good idea at the time.
CCC carburetors (look for the wires) have a Mixture Control solenoid or MC solenoid inside the carburetor which can be turned on and off by the ECM. When the MC solenoid is turned on fuel delivery is restricted and the engine will run lean. When the solenoid is off the engine will run rich. Pulsing of the MC solenoid is the sound you hear coming from under the hood of the car when you turn the ignition key on.
Close up internal view of CCC carburetor. Let's look at what happens when the MC Clearly visible are rich and lean stops for solenoid is energized so we can under- Mixture Control (MC) solenoid. MC solenoid is energized in this picture.
stand exactly what the ECM is trying to do. First off, the solenoid runs hot, meaning that it is wired to B+ and then all the ECM needs to do is ground the wire and the solenoid will be energized. This ECM controlled switch is called a "Driver" or "ECM Driver".
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When the ECM grounds this circuit, current flow energizes the MC solenoid. An electromagnetic field is developed. This field pulls down a metal plate, about the size of a postage stamp, mounted just above the solenoid inside the carburetor. This plate is normally held up by a high quality spring. When the plate comes down two things happen. Fuel is reduced because the metering rods are pushed down into the main metering jets and an idle air bleed is opened which allows air access between the idle tube and a fuel channel restriction. In simple terms ...when the solenoid goes on fuel is reduced and air is dumped in.
gas stream so that it can get a reading on the amount of' oxygen in the exhaust AN OXYGEN SENSOR gases. SENSES OXYGEN. An oxygen sensor is a voltage generator, it makes voltage chemically...that is correct. The oxygen sensor is a sophisticated device which uses several exotic metals which will This combined action will make a big produce electricity when heated in the difference between rich and lean condi- presence of oxygen. tions and gives the ECM a wide range of control over engine operation. This book Let's look inside this sensor. It screws will not attempt to get into specific ad- into the exhaust so exhaust gasses can justments for any carburetor, only to pass over the face of the sensor. The provide a general theory of operation. sensor is hollow so that normal air can get Overhaul and adjustment of carburetors to the inside of the sensor. When the is a science by itself. sensor gets hot a voltage is produced because of the difference in oxygen conAn oxygen sensor is placed in the exhaust tent of the two air surfaces.
For instance, if the sensor were simply hot and hanging out on the end of a rope in the middle of the shop then the oxygen THE OBJECTIVE 15 TO MAINTAIN content of the air inside and outside the OPTIMAL AIR I FUEL RATIO FOR : sensor would be the same with no differ- 1) EMISSION CONTROL ence in oxygen content, thus no voltage. 2) FUEL ECONOMY Now back to the car. With exhaust gases going over the sensor there is a difference in oxygen content between the two air masses. If you add more fuel you will have less oxygen in the exhaust stream because it will have been burnt up in the combustion process. If you remove fuel then you will have more oxygen in the exhaust stream. The greater the difference in the oxygen between the two then the greater the voltage produced.
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Oxygen sensors are designed to produce voltage over a range of .l to .9 volt. They are designed with a .45 volt mid range or center. If a voltage greater than .45 is produced the engine is said to be rich, all the oxygen has been burnt up. Less than .45 volt and the engine is lean, because there is a lot of oxygen in the exhaust stream which has not been burnt up. The ECM will adjust the on time of the MC solenoid so that the oxygen sensor voltage "toggles" or pivots around .45 volt. If the ECM cannot do this job properly then the Check Engine or Service Engine Soon light will come on and a Code will be set for the rich or lean condition which the ECM cannot correct.
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THE OBJECTIVE 15 TO MAINTAIN UP'TIMAL AIR I FUEL RATIO FOR : 11 EMISSION CONTROL 2 ) FUEL ECONUMY
CADILLAC HT-4100 USES A DUAL
Electronic Fuel Injection is one of the THROlTLE BODY FUEL INJECTOR. best systems to come along in the history IN,IECTORS FIRE ALTERNATELY WHEN of automotive technology. It is simple, REFERENCE SIGNALS ARE RECEIVED BY precise and reliable. EFI is a "single THE ECM. point" fuel delivery system meaning that all the fuel to the engine is supplied from a central location by one or two fuel injectors. Using the reference signal to the ECM provides accurate information about crankshaft position and engine rpm. Each time the ECM receives a reference signal the ECM will pulse the fuel injector. This means that short pulses of fuel are delivered into the intake manifold at the same point as the carburetor used to be placed. Each pulse of fuel will be metered to provide the necessary fuel for each cylinder needing an air and fuel charge. If you take a timing light and hook it to the ignition coil wire you can see the fuel
pattern delivered from the fuel injector. If you push the Throttle Position Sensor or TPS down with the timing light installed, you will see extra pulses of fuel being delivered since the ECM interprets this action as acceleration. Since you do not have an accelerator pump then you will need this extra fuel to prevent a possible tip in hesitation. If you put a vacuum pump on the Manifold Absolute Pressure sensor or MAP sensor you can cause the engine to stall because fuel delivery can be cut back or cut off entirely. The ECM will interpret this high vacuum as high deceleration with closed throttle. If you spend time around the circle track you know that carburetors have to be rebuilt several times a season because the gaskets are simply sucked into the carburetor. Imagine how the racing carburetor will go wide open down the straights and then at high rpm have the throttle valves snapped shut as the car slows for the corner ...lap after lap. The ECM says that with high vacuum in the intake manifold and with low TPS voltage that you do not need fuel, so the injector is simply not turned on at all. EFI generally works in a Synchronous mode, meaning that for every reference pulse you get a shot of fuel. However, it can also work in an Asynchronous mode under acceleration or deceleration when synchronous fuel delivery just will not do the job right. Another example of asychronous fuel delivery occurs with Prime Pulses which occur on some engine systems. Prime pulses occur with a cold
DUAL THROlTLE BODY INJECTORS ARE USED ON MANY DIFFERENT TYPES OF 6 AND 8 CYLINDER ENGINES. ALL SYSTEMS WORK VERY SIMILAR. THE DUAL THROlTLE BODY "CROSSFIRE" ALSO ALTERNATELY PULSES EACH INJECTOR. AIR LEAKS CAN RESULT IF THE TOP "0" RING LEAKS. FUEL LEAKS CAN RESULT IF THE BOlTOM " 0 " RING LEAKS.
engine to get it started. Since you do not have an accelerator pump to provide that extra fuel to get the car started in cold weather prime pulses will be delivered before you start cranking to get fuel into the engine. The ideal airlfuel ratio for the engine is 14.71b of air to 1 lb of fuel when the engine is warmed up. When the engine is cold, 20 below zero, then 1.5 to 1is the ratio. Carburetors have chokes, EFI likes asynchronous prime pulses.
Port Fuel Injection is the most precise fuel metering system used in today's automobile. Fuel is metered independently to each cylinder in this system. A fuel injector is mounted in the intake manifold so that it will spray fuel directly on top of the intake valve. This method gives the highest degree of response and increases both performance and economy. Fuel injectors can be pulsed on together or sequentially. Most systems pulse each injector on every revolution of the crankshaft. This means that an injector must be turned on twice in order to deliver the correct amount of fuel for each intake cycle. Sequential systems deliver the full fuel charge when the intake valve is open so that the engine will use this amount of fuel for the next compression and power stroke.
PORT FUEL INJECTION SYSTEMS USE AN INDIVIDUAL FUEL INJECTOR FOR EACH CYLINDER. BUCK GRAND NATIONAL TURBO SEQUENTIAL SYSTEM SHOWN ABOVE. 3.8 MFI SYSTEM BELOW.
It is important to remember that fuel travels from the in-tank mounted fuel pump, through the fuel rail and to the fuel pressure regulator. The fuel pressure regulator has a connection to the intake manifold with the objective to maintain about 35 psi across the injector throughout engine operation. Although EFI and PFI fuel pumps look basically the same they are not. EFI uses a twin turbine generating about 12 psi. PFI pumps can generate 60 to 90 psi. There is an internal relief valve in the pump if a fuel return line were to become restricted producing high fuel pressure.
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PFI THROlTLE BODY ASSEMBLY
THROTTLE
I A C
PORT FUEL INJECTION
COLD START INJECTOR
PRESSURE REGULATOR
Cold Slarl Injecioc is mergized to provide extra luel when lhermolime 4 t h is closed.
INTAKE MANIFOLD VACUUM
/
PRESSURE
CRANK FUSE
TO STARTER SOLENOID
SPRING
Cold dort injeclor is no1 found on all qines. II is only enerqized when the crank motor is energized.
I THERMO TIME SWITCH
I #,1
FUEL RETURN TO TANK
8 SECONDS MAX
COLD START VALVE
PORT FUEL INJECTION
FUEL SYSTEM
Sensors provide the ECM with vital information necessary for the job of maintaining proper air / fuel ratio. Just as most people have the senses of: sight, hearing, touch, smell, and taste; theECM needs its sensors also. Just like people, if the ECM loses a sensor it can continue to operate but it's performance will be impaired to a certain degree. This statement being true with exception to the reference signal. If that signal is lost then the fuel injected car will not run. At this point in our study of the ECM controlled automobile several things need to be stated. First off, we have already covered the basic principles of engine operation for fuel injection. This being that the engine receives fuel from fuel injector(s) based upon a controlling signal from the ECM. A decision is made by the ECM to inject fuel based upon engine rpm and engine load.
and 4) injector resistance. Although this detailed procedure is designed for PFI it also applies to EFI. Included in this book is a "Fuel Injector Test Procedure." Reference and use this testing procedure. If you do use it, you will quickly be able to determine if you do in fact have a fuel problem. Remember that this book is written for you, the fellow turning the wrench. You do not get paid to diagnose. You get paid to fix. Way back in the old days it was: 1) fuel, 2) ignition, and 3) mechanical problems which occurred. Today there is 4) electronic. You must know which area to look in before you can fix the car. If you think the car has a fuel problem run the test. If you run the test you will know whether or not you in fact have a fuel related problem. If everything checks out then proceed on to areas 2), 3) and 4). Now that you're a professional 1) fuel expert {and you will be if you use the test!) let's move on into area 4), the electronic domain. Before we do...let's see...2) has already been covered and 3)...well if you feel unsure about general mechanical then you better take some classes or read a ood book. If you insist upon using 1/2" rives on 114"bolts then this book is not for you.
If you understand this relationship between ECM and fuel injectors you are well on your way to success with the fuel system. Do not forget that an in-tank fuel ump pressurizes the fuel system. TBI Re1 pressures would be between 8 to 12 psi. PFI fuel pressures range from 28 to In summary, the fuel injection system is 42 psi, with turbocharged engines reach- very tough in the beginning. However, ing 50 psi. since injection is a precision fuel metering method it can be checked and evaluIn your diagnosis of the fuel system you ated in a logical and orderly way. After need to check 1) fuel ressure, 2) how you do check it you do not need to remuch fuel is injected, 3 wiring harness, check it.
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THROTTLE BODY One of the most important sensors is the Throttle Position Sensor or TPS. This device provides the ECM with a signal concerning where your right foot is. Are you accelerating, decelerating or maintaining speed? The first indication of change comes from the TPS. Your input to the engine is through the accelerator pedal, which just happens to be connected to the TPS. The sensor is attached to the side of the throttle body and is actuated (moved) by the throttle shaft going through the throttle body. When your foot moves the accelerator cable and opens the air valve the TPS is also moved. This movement tells the ECM that you are accelerating and that extra fuel is needed. Inspection of the TPS reveals that it has a 3 wire connection. One lead is a 5 volt input from the ECM. Another lead is a ground. Between these two outside leads is the TPS signal for the ECM. Internally the TPS is a rheostat capable of giving the ECM voltage changes in thousands of a volt!
THROlTLE POSITION SENSOR (TYPICAL TYPE D I A G M )
AorC
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TPS CHECK A TPS sensor is designed to provide throttle position voltage to the ECM. We will check this voltage to check sensor operation. Insert jumper wires or use the CHAT tool. A scanner will give you a voltage reading if there is voltage coming back but it is not accurate enough if your problem car has a hesitation or surge driveability problem. There are three wires and we need to check each of them. Use a high impedance digital multimeter such as the Kent Moore J34029A or equivalent for all tests. Test 1. Input power to TPS of approximately 5 volts. Test 2. Ground wire has proper continuity. Test 3. TPS voltage signal output. Initially check with multimeter on 20 DCV scale for maximum Wide Open Throttle (WOT) voltage. Do not be alarmed if it will only go to 3.5 v., on some cars this might be the case but generally 4.5 will be the high reading. Return throttle to idle. Set DMM on 2 DCV scale. You should get readings in .001v. changes. If you get erratic or jumpy voltage changes then your TPS may be deteriorating or coming apart inside. You may need to use a small screwdriver to move the TPS control arm for voltages up to the meter limit of 1.99%. With practice you can get the TPS to give voltage readouts in thousands (.001) of a volt.
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DIGITAL MULTIMETER
TPS VOLTAGE CHECK
Remember, if TPS voltage changes the ECM will think you want to accelerate or slow down. When a TPS starts to deteriorate and flake apart internally erratic high and low voltages will come from the sensor. The rheostat is electrically conductive. When it comes apart and you have an electrically conductive "dust" you will get jumpy voltage readings. Cars which have the EGR near the TPS experience a higher degree of TPS failure. Any time you see these two close together check very closely because of the heat which comes off the EGR has traditionally been very hard on TPS sensors.
Coolant temperature sensor provides a signal to the ECM which is used for fuel delivery calculation and other temperature related functions. Temperature readings are provided by a circuit which uses a thermistor which is a specialized resistor that changes resistance according to temperature. A signal voltage is sent to the coolant temperature sensor from the ECM. The ECM will then interpret this signal as engine temperatue. When the engine is very cold a high voltage reading will be observed. As the engine warms up the thermistor resistancewill drop and so will the signal voltage. At normal engine operating temperature the voltage reading will be between 1to 1.5 volt. If the coolant temperature sensor were to go open or the signal voltage wire to it were to become open the ECM would see high voltage. High voltage would be interpreted as very cold conditions. Very cold conditions would mean lots of fuel for "choke" type conditions. It is possible that the engine would be over fueled and could not start under these condtions. Manifold air temperature sensors tell the ECM what temperature the incoming air is. This reading is used in the fuel ratio calculation. MAT sensors can be mounted in the air cleaner assembly or in the intake manifold.
Coolant Temperature is used by the ECM to Control: * Fuel Delivery Coolant Temperature may be used by the ECM to Control or Modify: * Electronic Spark Timing * Idle Air Control * Exhaust Gas Recirculation * Canister Purge * Cooling Fan * Electronic Spark Control
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THERMISTORS CHANGE RESISTANCE WITH TEMPERATURE
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COOLANT
TEMPERATURE TO
COOLANT TEMPERATURE SENSOR READINGS
Degree 21 0 160 100 70 32 20 0 -40
F
Degree C 100 70
38 20 0 -7 -18 -40
O h m s Resistonce
185 450 1,800 3,400
10,000 13,500 25.000 100,000
An automobile engine is an air pump. Whenever the intake valves open a certain amount of air enters. If you have a turbocharger there will be boost pressure applied which will force even more air into the cylinders. The faster the engine spins over the more air you move, thus the need for better intake, cylinder head and exhaust design.
In order to make the most power and have optimal economy the ECM must know just how much air is entering the engine. Manifold Absolute Pressure or MAP sensors are used to provide this information. At sea level atmospheric pressure is about 30 inches of mercury and decreases about one inch per thousand feet of elevation. Therefore, at Denver the "Mile High City" atmospheric pressure would be about 25 ifiihes of mercury. A car in Denver would not have as much air entering its cylinders and would not make as much power. If the same amount of fuel were to be injected then the engine would run rich.
Manifold Absolute Pressure sensor provides ECM with reading on how much air enters the engine.
Barometric pressure sensors are used so that the ECM will always know what atmospheric pressure is. However, it became evident to GM that under wide open throttle conditions intake manifold pressure was the same as barometric MAP sensors tell the ECM how much pressure sensor readings. This fact led to pressure will be moving air into the cylin- the elimination of the barro sensor beders. A silicon chip is diaphragm cause the ECM was reprogrammed to mounted so that it will flex according to accept engine crank and wide open the applied intake manifold absolute throttle MAP readings for barometric pressure. Chip deflection is electrically pressure. Whenever you start the car a transmitted to the ECM so that an accu- MAP value is taken and whenever TPS rate pressure is provided for fuel calcula- voltage indicates WOT the MAP value is tion. I updated.
Electronic Spark Control is a system designed to provide the ECM with information concerning engine detonation or spark knock. A piezoelectric knock sensor is screwed into the block and it produces voltage when vibrated or shook at the frequency of spark knock. This signal is used by the ECM to retard spark timing of the Electronic Spark Timing program. The knock sensor provides an electrical input when spark knock occurs. This input will turn on a transistor and thus takes away the voltage signal the ECM should be receiving from the ESC Module. When the ECM notes that the input voltage has dropped, spark timing will be quickly retarded.
ELECTRONIC SPARK CONTROL
I
IGN B+ ESC SIGNAL E C M
1-l 1 ESC MODULE
--
-
KNOCK SENSOR
~iezoelectficKnock Sensor is screwed into the block and produces a voltaga when spark knock vibrations occur.
After timing has been retarded, up to the limit of 20 degrees, timing will gradually be brought back up to the value the ECM would like. Timing can be retarded at the rate of 2 degrees per second and it can be advanced at the rate of 1 degree per second. It is possible for the knock sensor to produce voltage when things other than timing shake it at certain frequencies. Connecting rods, piston slap, bad bearings, loose sheet metal and just about anything else which can make a good "rap" will set it off. Also, if the ESC wire leading to the ECM accidentally gets near a spark plug wire voltage could be induced into the ESC wire from the ignition system.
Screw the knock sensor into the block to 14 ft/lb of torque, with antisieze applied to the threads. Over torque and it would be like trying to wear a pair of shoes one size too small...whenever you put your foot down...OUCH...all day long. If the wire comes off the sensor, the engine could be damaged because the ECM would not receive the warning signal from the sensor.
Mass Air Flow or MAF sensors are very accurate devices designed to measure the mass of the incoming air to the engine. When the temperature is low air becomesvery dense. When air is hot it is less dense. Fog staying low to the ground or warm thermals rising are examples of dense and light air. Optimal air / fuel ratios are based upon weight (mass x gravity) and not upon volume. Want a quick test? Take a Coke bottle and put it in the freezer until it is cold. Put a balloon over the bottle's mouth. Set the bottle out in the sun. This will be a good example of how air expands when heated. Incoming air passes over the air temperature Two types of MAF sensors are in use. Most common is the metal foil sensing element using a postage stamp size sensing element and a temperature sensing thermistor. The metal foil sensing element is heated above the temperature sensor and the amount of heat required will allow the ECM determine air mass. On 5L and 5.7L V-8 a hot wire MAF is used. A small wire is cooled by air flow. This value is used to determine air mass.
sensing thermistor, through an air direction tube and over the metal foil sensing element.
Carefully inspect the metal foil sensing element. If the two metal layers separate an air pocket will be formed around the ceramic coated wire sandwiched between the foil layers. Air will insulate the wire so less energy is required to maintain wire temperature which will cause the If the MAF tells the ECM that no air is ECM to deliver less fuel than the engine flowing the engine will run rough because needs. This can be a major problem of a lean condition. If it tells the ECM the before the engine goes into Closed Loop operation. air is dense a rich condition can exist.
EGR Systems Operation Exhaust Gas Recirculation or EGR is one of the most misunderstood engine systems. If you had a way to change engine displacement, get better fuel economy, and reduce emissions all at one time that would be good. EGR does that for you. I realize that you hate EGR, everyone hates EGR, right? It's just what you've heard since there was an EGR. Let's look at this technically for a minute and then if you still hate it ...well, then that's up to you. When a piston goes down, air and fuel are sucked into the combustion chamber. A strong vacuum is created. If the throttle valve were opened the vacuum would go away and you would have atmospheric pressure blasting into the combustion chamber (review the MAP sensor if you need to). The engine has to work very hard to make that vacuum. It takes energy to do it. If you could reduce the vacuum your engine would not have to work so hard on the intake stroke. When the EGR valve opens and some exhaust gases are admitted back into the intake air stream this high vacuum will be reduced somewhat. The engine will not have to work as hard on its intake stroke.
ECM controlled vacuum turns EGR on.
Exhaust gases are inert. Oxygen used in the original combustion process is gone. EGR will dilute the new air charge. Inside the combustion chamber and on the power stroke, ignition will be slightly slower producing a longer cleaner fuel burn. Slower burn will reduce exhaust temperatures and reduce oxides of nitrogen or NOx ...that is why we don't have 11/1compression anymore. If your eyes burn in the shop because of a particular vehicle NOx is probably the reason.
EGR Diagnosis Does the EGR valve work? Take a hand held vacuum gun and hook it up to the vacuum fitting. When you apply vacuum the engine should falter or even die. This EGR valve is working. If you pull a vacuum and nothing happens then you have found the problem.
I have heard of cases where technicians have found ball bearings and other things in EGR vacuum control lines to cut off vacuum to the EGR valve. This will create a driveability problem including hesitation, shaking and surging. When the vacuum line starts to harden up vacuum will slip around the block activating the EGR. Therefore, the EGR valve will When the ECM turns on the solenoid, vacend up being on at times when it really uum is applied to both EGR and vacuum ought to be off. Remember, the EGR is diagnostic switch. off at WOT; so for all the performance people why let it bother you anyway? There are three types of EGR valves: positive back pressure, negative back pressure and ported. They all do the same thing with respect to permitting exhaust gases back into the intake as necessary. You can refer to the pictures if you are interested in the particular workings. It is very important that if you do change an EGR that you install the same type as you find on the vehicle. You will have a problem if you install the wrong type.
flc +SOURCE V r n M
12V
ECM EM SOLTNOlD
EGR VACU)M DIAGNOSTIC
ORN
m C H
EM
1.1.11
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DWOSTW: M C H
EGR OFF: Engine Cold In Park or Neutral Wide Open Throttle TPS Reading Low
EGR DENTFEATION
D IA
16648727
In order for the ECM to be sure that the EGR is working when it is supposed to be ASSEMBLY PART RAHl NUI.BER two types of diagnostic sensors are used. COOE D I A 06641727 The EGR vacuum diagnostic switch is 6314 P closed when vacuum is applied to the [ P I -- P 0 8 M FfEGSUR [N] - - MEGb,rmE BACX PAEffiURE BULT EGR valve. Note that vacuum first goes [ 1--W-POAlEDVALVE through the controlling vacuum valve when the ECM turns the valve on. Vacuum passing through the valve is applied to both the EGR and the vacuum diag- TEMPERATURE nostic switch. If the ECM turns the solenoid on, by grounding the control power circuit, the ECM expects to see a circuit created through the vacuum diagnostic switch. If this circuit is not completed the ECM will think that no vacuum is going to the EGR so the Check Engine or Service Engine Soon light will be turned on. If the ECM sees a circuit created by the vacuum diagnostic switch and the ECM has not turned on the EGR the Check Engine or Service Engine Soon was encased in a ceramic centered, metal jacketed body which in turn would thread light will again be turned on. into the outside of the EGR flow passage Also used to keep the EGR system housing. The sensor does not actually monitored is a heat sensing switch which touch the exhaust. It gets heat from the is used on certain engines. This is a housing where the exhaust gases pass normally open, thermally controlled through on their way back to the intake switch, which will close when it reaches manifold. If the switch breaks loose inabout 600.F. This switch closes and cre- side the ceramic an open circuit will ates a signal for the ECM to know EGR develop and the the Check Engine or is working. These switches have had a Service Engine Soon light will be turned high failure rate because the sensor is on. Under these conditions carefully fragile. The switch is attached to the end inspect the temperature switch. Be careof the connecting wire. Then the switch ful, it is very fragile. BAa(
Engine idle speed is determined by the ECM and is controlled by the Idle Air Control valve. When the engine is cold idle speed is increased similar to a standard carburetor choke. As the engine warms, idle speed will be reduced. Inside the throttle body an idle air control passageway permits air to move past the "pintle" which is moved in and out by the small motor of the IAC. There are two windings used to move the pintle, one winding extends the pintle and the Idle speed is maintained by the IAC which is other winding retracts the pintle. Air mounted in the throttle body assembly and passing the pintle maintains idle rpm. is controlled by the ECM. When the car is at cruising speed the IAC will totally close off the air passage allowing the throttle body to totally control air entering the engine. When the engine is turned off the IAC motor will seat the pintle and then retract the pintle about 213 so that the engine will quickly start when the engine is next cranked. IAC operation will maintain engine speed during warm or cold operation for optimal performance.
It is important that VSS wires leading to the ECM not accidentally be placed near other high voltage wires. Such a condition could induce a voltage signal into the VSS wire which would affect signal interpretation by the ECM.
BUFFER CIRCUIT
VEHICLE SPEED SENSOR
In order for the ECM to maintain proper control of engine and transmission functions,vehicle speed is needed as an input. This important reading is provided by either an optical sensor mounted in the speedometer head or a Permanent Magnet or PM generator mounted in the transmission. Readings provided by either sensor will be in the form of a square wave voltage reading. An increase in speed will produce an increase in the number of waveforms received over a given period of time. The ECM will take the square wave frequency and compare it with the ECM internal clock. This frequency comparison will be used to determine vehicle speed.
With the optical type sensor, any foreign material either on the rotating vane on the speedometer cable or on the optical sensor will affect the VSS signal. If there is a problem with this sensor be sure to check the rotatingvane. There have been recorded cases of grease affecting the sensor. Grease can be forced onto the vane and sensor by pressure speedometer greasing techniques. These unacceptable techniques include both grease nipple fittings which can be attached to the cable end by the transmission for quick grease application and by someone greasing the cable by using shop air presssure to simply blow grease up the cable using some cup grease and a rag over the end of their air nozzle. D o not use these techniques, they will produce major problems.
PM GENERATOR
WIRING HARNESS CONNECTOR
CHARCOAL CANISTER VACUUM W M l F C C
/ SOLENOID
AJRUV&V€
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-
ECM WMROLLED PORlEDVAalUM
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The ECM controls a vacuum source which will be applied to the canister purge valve. With vacuum applied a diaphragm valve will be lifted. Lifting the valve will cause airflow through the canister because of the applied ported vacuum or pcv connection. A filter on the bottom of the canister will allow air to enter the canister. If the canister purge valve leaks then the engine will run very rich until the canister is finally empty of fuel vapors. This condition will be aggravated by heat soak conditions which would fill the canister. To check the canister there are two checks. First, hook a short length of tubing or hose to the lower port and try to blow through it, there should be no flow unless the canister has a small purge hole which will only permit a small amount of air flow. Next, apply a hand held vauccum pump and apply 15" Hg. for 20 seconds. If the diaphragm does not hold this amount of vacuum then replace canister.
Evaporative Emission Control System (EECS) is used on all vehicles to reduce fuel vapors which would escape into the atmosphere. A canister containing activated carbon (charcoal) will soak up fuel vapors when the vehicle is not running. When the vehicle is running, captured vapors will be purged from the canister by using engine vacuum to pull these vapors into the engine so that they can be consumed during the combustion process. Visually inspect the canister for evidence of cracks or other damage which will Canister purge will start after the engine require replacement. If fuel leaks from has warmed up and gone into closed loop the canister it will have to be replaced. operation and when TPS throttle signal The filter on the bottom of the canister is to the ECM indicates that the throttle is a replaceable item. If it is dirty or has off idle. been damaged replace it.
SECTION 2 DRIVEABILITY DIAGNOSIS In this section a "systems" approach will be used to determine which system is causing the driveability problem. Analysis by "systems"will allow you to determine if: fuel, ignition, mechanical or electronic systems need attention. In Section 1the general building blocks of today's electronically controlled automobile have been addressed. In Section 2 these building blocks will be incorporated into systems so that a procedure or method can be followed to logically determine where you will need to concentrate your investigation. If the "Service Engine Soon" light, which used to be called the "Check Engine" light, is on then pull the ECM codes. Jumper A to B of the ALCL and read the flashes for code determination. Use these codes to help you in diagnosis. These procedures are discussed in detail in this section. Page D32 lists codes. No vehicle will have all of these code possibilities. If you use a scanner refer to the scan related material included in this manual to speed your diagnosis. Be careful that you read your scanner properly. Scanner manufacturers include an instruction manual with their equipment. If you have not read this information then you need to spend some time with your scanner manual. CHAT the Computer Harness Adaptive Tester is included in Section 2 so that you will be familiar with its operation. CHAT represents a natural extension of diagnostic equipment, incorporating accepted factory service methods, used for analysis of automotive engine electronics. CHAT can be used by itself or you can use a scanner with CHAT installed. CHATdoes not affect the ECM "mode of operation" like the scanner does. Voltage is the "language" of the ECM. CHAT was designed with one specific objective: to provide you with easy access to each wire of the ECM. CHAT allows extremely quick voltage and continuity checks for all ECM wires and circuits. You need to know and understand what these voltage readings represent in order to service today's cars and trucks. That is precisely why you are reading this book! So you will have a better understanding of automotive engine electronics. You need to be able to interpret and understand the "language" of these electronic components in order to be successful in what you are doing. Define success as the increase in the size of your paycheck after you understand how all of these electronic items make the engine work.
Troubleshooting requires that you be able to determine what is causing the problem with your car. Whether you have been in the automotive trade for many years or only a few years it is still necessary to approach a problem automobile in a logical and organized manner. Somewhere you have probably looked at some book that has told you about how to approach a problem car. However, I really doubt that the author of that book asked your problem car if it could read in order to cooperate with his book! Let's get serious. There are potentially all sorts of ways to attack this problem of driveability,which we will define as any sort of problem relating to the way the engine and powertrain work, but lets look at a method which will hopefully be very logical to you. I have been diagnosing and fixing cars for many years and there are several things which must work as Systems or else your car will not run properly. My personal background strong point is in engines so I am approaching this problem of driveability from that of an engine mechanic or technician. If you happen to be a transmission expert then you may very well look at driveability from a totally different viewpoint ...such as the
engine being a boat anchor attached to your "perfectly good" transmission. However, I look at it from the other end, andwhat is bolted to the backof theblock is somebody else's problem. I might say you have a transmission problem and even be able to pull one apart but I make it a point to let the transmission guy be the "expert" on the inner workings of transmissions. I am the engine expert and I do not fix transmissions, or at least I would not admit to it if I did. There are many people in the automotive repair trade which claim to know everything there is to know about a car ....watch out for these guys. If you can, try to specialize in just a few areas so you can be the best in several areas. Learning new things is great but, the more you learn in one week, the smaller your pay check will be on Friday! In order to be an engine expert I have to have a quick and logical way of approaching engine related problems. Always use this method and you will never have to worry about second guessing yourself. The objective is to fix it right the first time which means that my first objective is to determine which system the problem is in. Then I will worry about what is specifically causing the problem. However, the first thing I always do is determine just which system is creating the problem.
A SYSTEMS APPROACH: FROM AN
PORT FUEL INJECTION
ENGINE SPECIALIST'S POINT OF VIEW.
There are four systems which we need to use in our evaluation and diagnosis:l) FUEL, 2) IGNITION, 3) MECHANICAL and 4) ELECTRONIC. These areas do overlap, but if we organize our thinking we will be able to clearly define where one area is so that we can logically deal with the problem.
FUEL SYSTEM
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FUEL PRESSURE
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FUEL PRESSURE REGULATOR
FUEL SYSTEM. Consists of electric in tank fuel pump, supply lines, fuel filter, injector(s), pressure regulator and return line for all fuel injection systems. IGNITION SYSTEM. Consists of pickup sensor and the device it is sensing, ECM timing circuitry, HE1 control module, ignition coil(s), and connective wiring.
FUEL R
RETAINING CUP
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INJECTOR
MECHANICAL SYSTEM. Heads, block, intake, exhaust, nuts, bolts, belts, oil pump, camshaft, crankshaft, water Let's look at how a systems approach can pump,timing chain or belt, and similar so get us through the diagnosis quickly and accurately. Always start at the fuel syscalled "hard" parts. tem. If you do not have any fuel the car ELECTRONIC SYSTEM. ECM, en- will not run. If by chance you have bad or gine wiring harness, sensors, output de- contaminated fuel the car will run poorly at best. Our concern is fuel pressure, vice and ALCL. fuel delivered by the injector, and ECM injector on time.
F U E L TANK
I
F U E L PUMP
I
I
F U E L FILTER
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I
I
I
1
I
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PRESSURE REGULATOR
E
Verify ECM ground driver with engine running or cranking to pulse test light.
ENGINE
F U E L FLOW SYSTEM DIAGRAM
Fuel rail pressure should be within specifications. Supply the fuel pump with 12 volts through the fuel pump test lead located in the engine compartment or
12 volt will be applied with ignition on. Special 6 volt test lights are available which plug directly into harness. Regular 12 volt test light will work as shown below.
35 to 42 PSI
-
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+I2 VOLT
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ECM
12 VOLT
Spark plug wires should have a resistance of about 5,000 ohms per foot length. 2 foot long x 5,000 = 10,000 ohms
With the ignition system the first thing to ask is there spark coming out of the plug wire? Of course you could remove a plug wire, then take a small screwdriver, stick it in, hang near a good ground and crank the engine to see if a spark jumps. This is a "quick and dirty" method, but it is not 100% accurate. If you do have a coil problem then you will not have subjected the coil to a satisfactory test. Use a spark plug adaptive tester such as the ST 125 or simply remove the ground electrode from an old spark plug so that the spark will have to work harder to jump the gap. Be sure to attach a good ground to the body of your test plug.
IF YOU WANT TO FIRE TWO SPARK PLUGS AT THE SAME TIME, HERE IS HOW IT'S DONE.
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CAUTION: Distributorless ignitions systems have extremely powerful coils. If one or both wires are open or disconnected, you can receive a much more powerful shock than on conventional HE1 systems.
I
NO RECHECKS
I
't"Y
If this light blinks when the engine is being cranked, the ECM is receiving a reference signal from the ignition system. .*.
,
.
Mechanical systems benefit from a good visual inspection. In fact the first test you need to perform is a good visual inspection. When you jump to conclusions without carefully checking things out you always end up making an error in diagnosis. There are 15,000 parts in the average automobile. Your probability for a wrong diagnosis is high so take time to carefully inspect each vehicle before you make a final diagnosis. Electronic system consists of the ECM, wiring harness, input sensors and output devices. This is the last system to look at simply because it is the most difficult to deal with. If you have a "check engine" or "service engine soon" light then immediately deal with it. However, be sure and ask yourself "why" did this problem occur. If you have a vehicle which repeatedly blows up the same thing then you have been missing something.
ECM CONTROLLED OUTPUTS
ECM SENSOR INPUTS
Q E-49
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Electronic Control Module
0 0
q z ?
ROM
RAM
PROM
CLOCK I
A N A L O G SIGNAL
VOLTAGE
NEUTRAL
-
VOLTAGE
SIGNAL WAVELENGTH
-
DIGITAL S I G N A L O N TIME
OFF
CLOCK SIGNAL 1111111111111111111111111111111111111111111111 -
Sensor signals are converted from analog Analog signals can be continuously varito digital so that the ECM can process able in both voltage and frequency. Digital signals are variable but not coninput information. tinuously. Digital signals can be off or on, Digital signals are converted into binary yes or no, or high and low. This would be words which are processed by the ECM. called a digital binary signal. One level is On page D8 is a chart which illustrates a positive voltage, the other is novoltage. how the ECM can count up to 255, which As you can see in the above picture a means that all 8 switches are in the on digital binary signal produces a "square position. If the ECM adds 1more to 255 wave". all the switches will be turned off, representing "0".
D 8 Automotive computers do everything according to a detailed list of instructions which is called the program. Automotive programs take into effect all possible combinations of sensor input so that the best degree of driveability will result. For example, cutting off the a/c compressor when the TPS indicates wide open throttle, so maximum acceleration will be possible. A microprocessor functions as the "brain" of the computer, since it does all the necessary calculations. All other parts of the computer support the microprocessor. Since the microprocessor cannot store information it has specialized memories. ROMs, RAMs and PROMs are the memories of the automotive computer. Read Only Memories or ROMs are used for permanent storage of information, which is programmed in when the ROM is built. Random Access Memories or RAMs act as the file cabinet because temporary information can be stored and retrieved from there such as current sensor input values used by the microprocessor. Most RAMs are of the "nonvolatile" design and will lose their stored information if power is removed. Programmable Read Only Memory or PROM can be removed from the ECM. PROMs are used to provide the ECM with specific design and operating characteristics for each car model, even though the same ECM type may be used in several car lines.
ECM uses an "8 Bit" microprocessor. 8 segments make up each "word". 255 is the largest number which can be recorded with an 8 Bit chip.
-
AIR DIVERT SOLENOID
AIR DIVERT SILENCER
CHECK VALVE
-
FUSE & HOLDER
:kESSURE SWITCH
-
Scanners read what information is sent along the serial data stream. Scanners are extremely helpful, if you know what the heck they do and how they interface with the ECM. Scanners do not provide all the information. They do however, provide some very useful information and they also provide some information which on the surface may seem correct but can cause driveability problems. It is extremely important to understand just how far a scanner can take you concerning diagnosis. Were you aware that the computer is like a 4-speed transmission? You plug the scanner into the Assembly Line Communication Link (ALCL) or Assembly Line Diagnostic Link (ALDL), which are the same connector called different names by the various car divisions of GM. In this manual we will use ALCL to identify this connector, however if you see ALDL be aware that it is the same device. When you install the scanner onto the car you change the way the ECM operates. In fact the ECM has four modes of operation: open, diagnostic, fuel back up, and special or ALCL mode. Most scan tools are designed to automatically switch the ECM into the special mode of operation. Because of this many technicians are not aware of the other modes. This has caused many problems, such as trying to set engine idle speed and the scanner has sped the engine up to 1200 rpm, which is
ALCL Connector Terminal Identification
FEDCBA A - Ground Terminal B - Diagnostic Enable C - Exhaust Port Air Switching Solenoid D - Service Engine Soon Light E - Serial Data F - Torque Converter Clutch G - Fuel Pump Test Lead Not all terminals are found on all engines.
Create a circuit on A9 in order to receive ECM Serial Data from terminal E.
-,
SERIAL DATA
1 1
part of the ECM's programming when put into the special mode. Unfortunately, scanners can get you into trouble. When the computer is in special mode they cannot spend all of their time taking care of engine operation. Some functions become locked in because the microprocessor does not have time to deal with them because the microprocessor must take time out from its computing function to answer your questions ...such as integrator and block learn or any other request which you enter in your scanner.
Scanners apply specific resistances across the A and B terminals in order to change ECM modes of operation. Normal operating mode is called 20,000 ohm which is an open circuit with no connection.
DIAGNOSTICS
I
A9
Special mode is the only mode where you can get fairly reliable information, but you need to keep this in mind, fairly accurate not totally accurate. Scanners can also shift the ECM into the fuel back up mode where the engine will run on the calpac. Or, the engine can be put into open mode, where it normally operates. If the engine is in open mode you probably will not get accurate information. If you do get good information that'sgreat. But if you want TPS and with your foot flat on the floor your reading is .45 instead of 4.5 then I would not believe your scanner. The final mode of operation is the diagnostic mode where the scanner could ground the diagnostic terminal in order to flash the service engine soon light in order to use the light for code retrieval or check EST operation. Some scanners will not do this because of electrical circuit problems with the external power source from the lighter.
SCANNER
II
!-----------------------------I
MODE
A-B RESISTANCE A9 VOLTAGE
Open ALCL Fuel Backup Diagnostic
20,000 ohm 10,000 ohm 3,900 ohm 0 ohm
5.0 volts 2.5 volts 1.4 volts 0 volts
Integrator and Block Learn will both read 128 Integrator and Block Learn are two read- when the car is not in closed loop operation.
ings which tell you how much fuel the ECM is providing to the engine. These values can be read with the scan tool and are extremely important for you to understand.
m
u
0
1
SCANNER
As you are aware, the ECM will inject
fuel into the engine based upon sensor inputs. However, reference, throttle position and coolant sensors are the most significant inputs with the other sensors used to fine-tune fuel delivery. In the section which discussed the microprocessor it was covered that 255 was the highest number which could be recorded with an "8 bit" computer chip. If you Integrator and block learn work the same count the possibilities of 0 to 255 then 128 way. Integrator is the first value to move would be the mid point. and after a while block learn will move over to that point. However, now that the 128 is the mid point for both integrator airlfuel ratio has been corrected to the and block learn. If the engine needs right value (14.7 to 1) our integrator is additional fuel then a higher number will ready to take off in either direction again be registered to indicate an increase in as needed. For example with a small air injector on time. If the engine is rich then leak downstream from the mass airflow the numbers will be less than 128. sensor the ECM will think it's running lean because of the air which has not Now that we have covered the basic prin- been accounted for, thus it will command ciple of integrator and block learn, which a longer on time. Since this is a permaare two different values, let's explore nent condition, the block learn might be them in greater detail. Imagine that you 150, indicating extra injector on time, are taking a four year old kid to the toy with the integrator value at 128. If the air store. Whenever something new pops up leak were greater then both values would the kid is off and you sort of tag along. be permanently over 128.
Before the engine goes into closed loop More fuel is delivered due to a lean condition operation both integrator and block such as a restricted fuel filter. learn values will be fixed at 128. When the ECM gets a strong acceleration com( I mand both values will again be locked in SCANNER at 128. Injector on time of 128 does not mean that the injector is on 112 the time the engine is running. It means that the injector is held open 112 the amount of time which could possibly be allowed by the program in the PROM. There are limits to injector on time. On passenger cars 90 to 150could be the range. On performance vehicles the maximum on time could increase to around 200. 128
150
Less fuel is delivered due to a rich condition
An engine with a restricted intake or a such as a restricted air filter. restricted exhaust would run rich because it could not properly breathe. Thus the ECM would reduce fuel delivery in order to maintain 14.7 to 1. However, during full throttle bursts or engine warm-up a very rich condition would result because the full fuel charge would be delivered to the engine.
1128
90
/
SCANNER
If you have a scanner then make a note of integrator and block learn values with the engine idling in closed loop. Induce a small vacuum leak and note what hap- More fuel is delivered due to a lean condition pens. Partially restrict the air intake and such as an air leak. INT BLOCK note your readings. If you have a scanner, then integrator and block learn are two values which you need to closely check on SCANNER I each car. Remember, if the car did not have a problem you would not be doing this! Learn about these values, they apply to all EFI and PFI vehicles. Integrator and block learn values are two of the most helpful values you can get from the ECM on your scanner. -
Scanners can get you into trouble and you need to be aware of their limitations. Scanners receive all of their information from the serial data transmitted from the ECM. This information represents a "snapshot" of what the ECM has stored in the RAM. Therefore, there are certain readings which will appear to be correct but are not in fact accurate enough for your diagnosis. A very good example of this is TPS, and you should perform this experiment so that you will know exactly what limitations you are dealing with for scanners. If you access the scanner reading of TPS and compare it at the same time you have installed a digital multimeter on the TPS signal wire you will notice the difference clearly. Scanners will give you a TPS reading but this is not sufficiently accurate to set baseline TPS voltage readings. Set the DMM to the 2 volt dc scale and note the real ECM signal input. Compare this to your scanner. Move the TPS arm through a small arc and you will see that the sensor provides variances in thousands of a volt (.001). Scanners will vary but their variance is really only reliable to the first decimal place (.I). This degree of accuracy can cause the baseline setting where .45 volt (3.8 l), + or - .075 volt can really get you into trouble.
trouble. Technicians who have used the scanner to set TPS on CCC carburetor vehicles and have gotten away with it will cause driveability problems with fuel injection. Remember that canister purge and TCC are ECM outputs which look at the TPS signal. When you install the scanner in the diagnostic mode you will not always get the proper diagnostic codes. Always perform a Diagnostic Circuit Check and then use your scanner to rough out the problem area affecting your subject vehicle. If you use the scanner in any mode other than the ALCL 10K mode you need to be extremely cautious of any reading you do get. If the coolant temperature is locked in at one value or the car stays in open loop, according to the scanner...switch to the ALCL mode and verify your reading. There is no sense trying to fix something which isn't broke.
Scan tools allow for a quick check of sensors and switches. Serial data only updates every 1.25 seconds and vibration induced intermittents will not necessarily show up on the scanner. Remember that the scanner interprets the sensor input wire. However the sensor functions as part of a circuit and thus any problem in Perform this little check and you will see the circuit will have some type of effect how easy the scanner can get you into upon the sensor reading even if the component is perfectly good.
Occasionally you will find a short to power where a wire will have come in contact with an unwanted source of power. This can come from defective insulation, or internal component failure so that current can pass through a component in a way it is not supposed to, or a physical connection existing between the two circuits in question. Knowing how to check continuity will allow you to be sure that your wires go where they are supposed to and only where they are Volts represent electrical pressure. supposed to. Measure volts at any point in the circuit. Amps represent how much current flows through a circuit, sort of like how wide is a river for example. Ohms act as the resistance to flow, the more resistance the less flow. Voltage readings of sensors is made by
Amps,volts and ohms are the language of today's automotive electronics. You need to know how to measure each of these values in order to service these vehicles. If you do not feel comfortable with amps, volts and ohms then review the sections of this manual which deal with these subjects. It is very important that you fully understand how these electrical characteristics inter-relate with each other.
installing jumper wires and attaching DMM.
Ohm's law is the equation used to express the relationship between these elements E=IxR. Volts = amps x resistance. Perform the diagnostic checks on each circuit so you will know just what is happening. Continuity checking will tell you that your wires go where they are supposed to. If you have a short it would be like trying to wash your car with a hole in the hose ...the water would not get to the nozzle. With a short the current is flowing somewhere it is not supposed to. Shorts generally occur to ground and tend to blow fuses and burn up wires.
DIGITAL MULTlMEl'ER
TPS VOLTAGE CHECK
Resistance measurments are made across the component.
Continuity checks are made with the circuit isolated.
0 200 OHM
Voltage checks are made when the circuit is operational.
Amperage checks are made by allowing all the current to flow through the meter.
20m DCA
Schematic diagram of circuit.
Continuity test of control wire to relay.
R+ 12v
.-. 0 200 OHM
10
RELAY 7
E C
B+ 12V
R E LAY
M L
-:$
-
-
-
-
-
COOLING FAN
$@= -
-
Continuity test of individual wire in harness. Disconnect ECM before testing.
SENSORS
Voltage test for each ECM wire is performed with with ignition on and idling in closed loop
High impedance digital multimeters are necessary to perform checks of the automotive electronic system. Throughout this manual you have seen it and now is the time to explain why you must use this type of meter. Remember the discussion of magnetism and how current flowing in a wire created a magnetic field? That technology is used in the older "swing needle" type of meter. Consequently, it takes a lot of current flow in order to make this meter work. Additional current flow can cause you problems because this type of meter can damage the sensitive electronic circuits of the ECM. The ECM has circuits which are primarily designed to handle 112 amp of current flow. There are "protected" ECM circuits which have greater capacity, such as the fuel injector drivers, but these are different than standard sensor circuits. By now you realize that a sensor signal can involve only a small amount of actual current because the voltage present will act as the information carrier. Older swing needle meters require so much current flow that they could totally consume some signals. High impedance digital multimeters require so little current that it is difficult to measure how much they would affect a circuit, out of the laboratory environment.
Pictures included in this text show how the meter is supposed to be used. Refer to the pictures if you have questions about meter installation. However, it seems that one of the most difficult problems is the reading of the meter itself. If you have experienced difficulty with really understanding all of the symbols and settings of your meter then you will need to do a little homework. You may not have done homework in years but this can be both fun and interesting! Take your digital multimeter and hook it up to some sensors which have variable outputs and take the time to understand exactly what you are doing. For instance, I removed the 3 wire connector to a TPS and set my DMM to the 20 K scale (K is 1,000 so 20 K is 20,000 ohm, the only 20K scale is for ohms on your meter). I inserted one probe into the center terminal and one lead into an end terminal. My meter said 1.8K. I moved the probe from the end terminal to the other end terminal and the meter read 5.15 K; this was correct. I moved the TPS throttle arm by moving the throttle valve and my meter resistance dropped to 1.8K, indicating wide open throttle. How did I know that I had originally installed the meter backwards? Ohm's Law, that's how. With high resistance the ECM, off the center wire, will read low voltage. So when properly installed, high resistance will
fall to low resistance and so the ECM will mentation until you really feel comfortable with your meter. Anyone who had see an increase in voltage signal. made it this far reading this book needs to Install three jumper wires to the TPS, or know everything about that meter. It is install the CHAT unit and perform this the device which will tell you if a problem test with the meter set to 20 DCV and exists. Have you ever seen the flashing turn on the ignition. Move the TPS lights of a police car behind you? Well, if through its' operating range. TPS should you have then you know that he's trying to vary smoothly. Just for the heck of it, if tell you something! you have a scanner hook it up and compare its' reading to your DMM, you will If you do not fully understand how that be shocked at how far off the scanner is, meter works you may have a problem especially with the DMM on the 2 DCV getting the message! Be sure to know all scale. Remember that most of your driv- there is to know about your meter. If your ing is done with TPS below 2 DCV. meter has a diode check, then go by your local Radio Shack store and pick up a Now let's try turning our attention to the diode assortment and try them. And, if oxygen sensor. Insert a jumper wire or you really start getting into this whole simply hook into the CHAT unit sensor thing, break down and purchase one of signal. Again, the DMM should be on the their "200 in 1"experiment kits when it is 2 DCV scale and you can see exactly what on sale. You will be able to build all sorts voltage you are generating. This is agood of things. Take that DMM and work it hookup to inspect for rich or lean run through some of these circuits. Figure conditions which would include canister out why diodes are in certain places. purge and vacuum leak diagnosis. Air Figure out why capacitors are placed as leaks will pull in propane if you use an they are in your circuits. A couple of enrichment tool. The meter will immedi- hours, when you can, this electronic stuff ately pick up any change in sensor output. will really make a lot of sense which will Remember to never try the ohm test help you out on the job. Remember, we across an oxygen sensor, it is a voltage want to do it right the first time! generator and could be damaged permanently because an ohmmeter placed energy into a circuit to make resistance checks. If you have problems reading the meter, take it home and play with it. Take along a couple of sensors and do some experi-
and cut to length will make a good connection. Remember to crimp and solder with rosin core solder to ensure that a good connection exists, just like with every electrical repair which you will make on the ECM wiring harness. Do not use crimp connectors! Or, you will have intermittents which will begin the Accessing all of the circuits is tough, it day the car leaves your shop! does require work and it requires circuit understanding. If you find that you need After you have your jumper cables and a particular type of connector then you wires you will have access to the wiring will need to make up some test jumper harness in order to make necessary connectors. These are available from checks with the DMM. Of course, you your friendly tool truck man and will do will need to know just what circuits you a good job. However if you find that you are checking and what types of readings need a specific type of connector which you are getting. These readings would has not made it into his selection yet, then then be compared with what you personyou need to make a trip to the junk yard. ally would anticipate them to be and you For a couple of bucks you can get all sorts would also reference the expected readof connectors which will fit the specific ings listed in the shop manual or in the reference section of this text. types of vehicles which you work on.
Now that you have mastered the DMM you are ready to get the information out of the car. By now you know that the scanner does not have all the answers, only some of them. Now we need to get to the bottom of things and that is where the DMM becomes your top tool.
Keep in mind that no reference is 100% right. That is why you need to have an idea about the reading which you are getting. Is the reading which you are getting from your DMM what you personally think should be coming out of that sensor? When you understandECM and wiring harness circuitry then you will feel comfortable making this type of decision. Of course, do not overlook performing the same test on a known good car, this is a good way to verify test If you are using the very small connectors results. then a paper clip of the proper diameter
After you have the connectors then they need to be prepared for service. Terminal ends need to be fitted to the ends of the connectors so that you can quickly install them to make your circuits operational. If you are using the standard "weatherpack" type connectors then these can be had from any GM dealer under part number 12014836 and 12014837for the male and female terminals.
CHAT, the patented Computer Harness Adaptive Tester, is the most significant new diagnostic test tool for GM cars and trucks. CHAT has been designed and built for the tune-up and electrical technician servicing highly complex engine control systems. Because of its interface features, CHAT is the most sophisticated service tool available to professional technicians. In recent years diagnostic computer interface systems have been developed to help with the service of complex automotive engine electronic systems. These devices can cost $18,000 and use an ECM interface terminal to provide vehicle data for analysis. CHAT provides a way to access each wire, sensor, solenoid, relay, and control used for all ECM engine functions. CHAT uses the exact same Packard Electric connectors which are in the original equipment wiring harness. All CHAT tests are performed with a digital multimeter and this data need only be compared with available diagnostic and ECM voltage charts so that necesi i sary decisions can be made in order to f the vehicle. CHAT costs about the same as a scan tool.
In order to fix the car you have to determine exactly what is wrong with it in the first place. Finding out what is wrong can be a difficult task ...especially if you do not have any idea about what is causing the problem. You must understand how the ECM system is designed to work if you want to fix it. There are logical service procedures for the electronic system. These procedures take into account the operational parameters and provide you with a logical sequence to approach driveability problems. In fact, after you become comfortable with the right way to perform diagnoses and you become confident with the fact that it is possible to fix the electronic system you will probably become very proficient with this system. If you use CHAT you will be performing voltage, continuity and short testing. These are the same tests you would be performing without CHAT only now these tests are easy to do. As you become more confident with
ECM operation you will be turning the corner into the newest area of automotive technology. Very few technicians are competent in this area. CHAT will help you achieve success with difficult driveability problems by making necessary diagnostic checks quick and easy to perform.
Performing voltage, continuity and short testing will have to be done if anything other than a simple sensor failure occurs. Perform a diagnostic circuit check and see what the ECM tells you. If you have a code then you need to deal with the code. Always start at the lowest code and work up, unless you have a 50 series code and then go immediately to that. To get the codes simply jumper terminal A to B in the ALCL and watch the service engine soon light. It will blink code 12 three times, followed by any recorded codes, and repeat the code 12 again. Code 12 will be one flash followed by a pause and then two flashes of the light. Code 34 would be three flashes, a pause, and four flashes, for example. See the reference section of this book for code identification.
If all of this activity up under the dash sounds tough; well it is, especially when you perform wiring continuity checks. However, if you have CHAT then these tests are much easier. If you have the CHAT unit simply remove the header connectors from the ECM which you do not need to remove. Leave the header connector wiring retainer combs in place and plug the header connectors into the CHATjunction head. Install the jumper harness from the junction head to the ECM and you have completed CHAT installation. To perform voltage checks from the CHAT pinout first verify the ground terminal using your DMM on the 200 ohm scale. If this ground checks then insert the black probe into the dedicated ground and simply select the circuits you need to check. Refer to the reference section of this manual as necessary. If the ground does not check out, attach the DMM black lead to a good ground and perform the tests. If your results do not match the reference values, inspect the engine grounds. The dedicated CHAT ground is tied to one of the engine grounds which use terminal A-12.
If the sensor checks out then you need to go into the wiring. You will need to drop the ECM from its mounting and see just what voltage is getting to the ECM on the appropriate circuit. After you remove the ECM you will need to remove the retainer comb in order to gain access to the back of the wire entering the ECM header connector. You can now use the exposed wire end in order to perform ECM header connector voltage testing Refer to the diagrams about installation or use the DMM and go from the appro- and voltage testing with the CHAT tool. priate terminal on the connector back to the sensor connector to verify wire continuity.
D 23 CHAT used in the performance of voltage and continuity tests.
Voltage tests are performed like this. b l u U M m
Continuity tests are performed like this after removing ECM
To perform continuity checks, first remove the two jumpers from the CHAT junction head to the ECM. You do not want your results influenced by the ECM. Insert one DMM probe into the appropriate CHAT pin out terminal and touch the other probe to the wire in the connector which would attach to the sensor or output. With CHAT continuity checks can be performed very easily. Without CHAT continuity checks must be made with one ohmmeter probe up under the dash stuck in the back of the header connector while you are out under the hood with the other probe. Without CHAT this vital test is difficult, slow, and not too reliable. To perform a short to ground use the same setup as for continuity with the ECM jumpers removed. Simply place one probe in the suspect circuit pinout and touch the other probe to the dedicated ground terminal. If the DMM shows continuity on the 200 ohm scale, then you will need to trace the wire. If your meter makes an audible beep when continuity is established you can shake the harness to speed diagnosis. Not all scanners will work with all GM cars unless the scanner has been appropriately updated with the annual changes. You can use your DMM on any
GM vehicle with header connectors 1 which will accept CHAT. I 1
I I
CHAT uses Packard Electric connectors which are the same type used to build the wiring harness. If you need to attach CHAT into a Body Computer or BCM you will have no problems. Be sure to reference the appropriate service manual for readings of the 24 pin and 32 pin connectors. CHAT will also fit the newer P4 computers, simply watch which circuit you plug into so that you do not get your circuits confused.
Electrical Danger
The ignition should always be off whenever removing or reinstalling ECM connectors.
GROUND PIN-OUT
CHAT
8
0000 A9 A 1 D A l l A12 @ 000 GROUND 09 BID E l l 612 00000000 C9 C10 C11 C12 C13 C14 C15 C16 00000000
CHAT PIN-OUT
COMPUTER HARNESS ADAPTIVE TESTER NSTALLATION AND IDENTIFICATION DIAGRAM
\ \
2 0 I N C H LONG 3 2 WIRE JUMPER CABLE
32 PIN WIRLNG H A R N E S S C O N N E C T O R
TO E N G I N E
TO ENGINE
\
24 W I R E JUMPER CABLE 2 0 INCH LONG
CHAT JUNCTION HEAD
CHAT is covered by U.S. Patent Number 4,690,475 CHAT is available from Diagnostic Products Company
24 PIN WIRING HARNESS CONNECTOR
VOLTAGE CHECK ALL ECM WIRES AND CIRCUITS LIKE THIS
COMPARE ACTUAL TPS VOLTAGE WITH ECM VOLTAGE IDENTIFICATION CHART OR SHOP MANUAL IF .724 VOLT WAS YOUR ACTUAL READING OF BASE TPS ON A PORT FUEL INJECTED CAR YOU WOULD HAVE TO ADJUST THE TPS.
IF TPS REQUIRES ADJUSTMENT FOLLOW SHOP MANUAL PROCEDURE TO LOOSEN TPS ATTACHMENT SCREWS AND ROTATE SENSOR UNTIL VOLTAGE SPECIFICATION IS SET. TIGHTEN TPS ATTACHMENT SCREWS ACCORDING TO SPECIFICATION.
SHORT TO GROUND OF THE DISTRIBUTOR REFERENCE SIGNAL WILL PFIODUCE A "NO RUN" CONDITION WITH A FUEL INJECTED VEHICLE.
0 200 OHM
Perform short to ground test like this.
32 WlRE JUMPER CABLE
\\ SHEET METAL SCRRN CALISES SHORT-TOGROLIND PRODUCING A NORUN CONDmON
24 WlRE JUMPER CABLE
CONTINUITY TEST SHOWS WlRE IS GOOD.
32 WIRE JUMPER CABLE
24 WlRE JUMPER CABLE
CONTINUITY TEST SHOWS WlRE IS OPEN (BAD).
32 WlRE JUMPER CABLE
24 WIRE JUMPER CABLE
"OL" READING MEANS OUT OF LIMITS
ADVANCED DIAGNOSTIC PROCEDURES
Use CHAT to Verify Series Circuits with an Ohmmeter. Many circuits are connected together. Components and wiring which make up an individual series circuit, can be checked for continuity at the CHAT Pin-Out.
p9 : 2 A$)pApgAgAg 82 0.l
20K OHU
B l 05 86 07 S B B l O B l l B 1 1
000000000000 CJ C4
C5 C6
C7
D
C) ClOClI C l l C l l
h%@0@00@~00@0 ot
M DI M
m
M 07 m
a o i o o t o~ n or,
\ COMPUTER HARNESS ADAPTIVE 1 \
I
ot4 01,
ota
MANIFOLD AIR TEMP
This is an example of how i t is possible to check sensors and wiring with CHAT. Place one digital multimeter probe into terminal D 2 of the CHAT pin-out. Then you will be able to check all wiring and sensors by continuity testing the individual series circuits, by using CHAT. Series circuits are formed between terminal D 2 and C10, C13, C14, and C12 in this example.
ADVANCED DIAGNOSTIC PROCEDURES
Use CHAT to Verify Powered Circuits. Many circuits are connected to a source of power. Components and wiring which compose each individual series circuit, can be checked for the presence of source voltage at the CHAT Pin-Out. Also, in this representative circuit, a functional test of the brake switch could be performed by simply pushing down on the brake pedal and observing the meter reading.
1
GAGES FUSE
IGN. 12 V. 12.2 VOLT
S.E.S. LAMP BRAKE SWITCH
TI
Inl
1 -
3
1
AUTOMATIC TRANSMISSION TCC SOLENOID
I
FIEIDICIBIA
I
I1
OVERDRIVE LIGHT
G I ) ] ( )
r-l M/T OVERDRIVE SOLENOID
CANISTER PURGE SOLENOID A3
12.2 VOLT
DIVERT SOLENOID
I
12.2 VOLT
-
1
(BLACK CONN.) A2
I
PORT SOLENOID
note: This diagram shows both automatic and manual transmission options available for this vehicle.
CIRCUIT TO GROUND
CHECK FOR CONTINUITY TO GROUND CHECK FOR CIRCUIT CONTINUITY
POWERED CIRCUITS
CHECK FOR APPLIED VOLTAGE
A TPS sensor generally has around 7,000
Systems testing can be done with CHAT in order to check and verify much of the ECM ohms resistance. Go between any two of wiring and sensors with voltage and continuity the three wires with the DMM on the 20 K (20,000 ohm) scale and you should test procedures.
haveacircuit. In this example the tests are between C14&lD2,C14&C13orC13&D2. Circuits are necessary for signals to come into and go out of the ECM. If you have a CHAT unit for GM vehicles, or a pinout for Ford or other vehicles, this section will be of great value to you. Take the necessary time to become familiar with CHAT and system testing procedures before you go out and attack any problem cars which come your way. Knowing how to use this tool and these procedures, will save you hours of time when trying to determine what is wrong with a so called "problem" vehicle.
Look through the wiring diagram and repeat this procedure. You will find and be able to isolate other circuits including complex circuits with interconnected sensors, switches or devices. Many circuits use the vehicle for ground. You can perform continuity tests to ground in order to verify these circuits.
With the ECM still disconnected, switch the DMM to the 20 DCV scale and turn on the ingition. The ECM will ground powered circuits in order to turn them Refer to page D 28 of this book, which on. Page D 30 illustrates that "powered" shows a conventional continuity check of circuits will be electrically hot and system a wire using CHAT. voltage should be present when checked.
Now, let's use a systems approach to continuity test the same TPS system. Use of a systems approach will greatly speed your testing procedure. Refer to the wiring diagram as shown on D 29.
Voltage and continuity systems checks can be used to verify most of the ECM circuitry and components. This is a valuable new procedure which significantly speeds diagnosis. This testing procedure is simply not practical without CHAT.
CODE IDENTIFICATION 12 - No reference (engine not running)
\ \
Thb b a check d the ECM to doid a signal and d m not indicate a problem. It dmply meana that you have no reference.
13 - Open oxygen sensor circuit
/ /
SERVICE ENGINE SOON
-
/
14 - Coolant sensor signal low 15 - Coolant sensor signal high 21 - TPS signal voltage high 22 - TPS signal voltage low 23 - Manifold air temperature low 24 - Vehicle speed sensor 25 - Manifold air temperature high 31 - Wastegate electrical signal -turbocharged engines. 32 - EGR failure
33 - MAP sensor signal high
To perform diagnostic circuit check insert jumper between ALCL terminals A & B. Read code flashes: blink, pause, blink blink as code 12. Note additional codes. Remove ECM power by disconnecting ECM fuse for 10 seconds. Start engine and see if code returns to indicate that problem actually exists. Some codes will require that vehicle be driven in order to duplicate conditions.
34 - MAP sensor signal low 35 - IAC problem 36 - Mass Air Flow
46 - VATS
41 - Cylinder select error
51 - PROM
42 - Electronic spark timing
52 - Fuel CALPAC missing
43 - Electronic spark control
53 - Over voltage condition
44 - Lean exhaust condition
54 - Low fuel pump voltage
45 - Rich exhaust condition
55 - ECM
Open loop operation exists until the vehicle reaches operating temperature. There are three things which must occur in order for the engine to enter closed loop operation. First, the oxygen sensor must warm up and start to produce an electrical feedback signal to the ECM, which occurs at about 600°F. Secondly, the coolant temperature sensor must show about 135°F. Thirdly, a given amount of time must pass so that engine rpm will have a chance to stabilize. Thirdly, there is a time element which will vary from 10 seconds on 1985 EFI and PFI models. This time element was lengthened to 30 seconds beginning in 1986. CCC systems will require about two minutes before entering closed loop operation. When closed loop operation is reached the ECM will maintain an air fuel ratio of 14.7 to 1for optimal emission and economy operation. When the vehicle is operating in open loop a rich condition will exist to promote engine warmup.
In closed loop operation the ECM will maintain a 14.7 to 1 air/fuel ratio.
TO ENTER CLOSED LOOP: 1. OXYGEN SENSOR SIGNAL 2. COOLANT TEMPERATURE 3. SPECIFIED TIME
Port fuel injectors can become clogged with a tar-like residue which will cut fuel delivery. Generally this condition results from the use of fuel which does not have sufficient detergent additives and can occur invehicles having a high heat-soak. Short trips in town can produce clogged injectors. In order to determine if there is an injector problem perform an injector balance test. Specifically, this test will determine if each injector delivers the same amount of fuel. This is accomplished by turning each injector on for a specific amount of time and recording the pressure drop on a gauge attached to the fuel rail. A suitable tool is the Kent Moore 5-34730 or equialent, which contains a pressure gauge, injector tester, and test light.
then injectors will need to be cleaned. If an injector falls outside of this range then repeat procedure. Do not fire injector more than three times or you will flood the engine and soak the spark plugs with fuel. If all injectors check within specification, check the injectors electrically. Install the test light and be sure it cycles when the engine is cranked. It is also good policy to take your ohmmeter and check each injector. Injectors may look the same but they can have different flow rates and different resistances.
If the gauge will not hold pressure then the fuel pressure regulator is probably defective and will need to be replaced. If you have very high fuel pressure look for a restricted fuel return line. If your fuel Install the fuel pressure gauge onto the pressure is low suspect a clogged fuel fuel pressure tap. Cycle the fuel pump filter or other restriction on the supply either by turning on the ignition and side. letting the pump cycle for two seconds or apply 12 volts to the fuel pump test lead. If an injector does not deliver sufficient Purge air from gauge line in this process fuel a lean condition will exist and preigto ensure accurate reading. nition can result. A vehicle surge can occur which will typically be very notiRemove harness wires from injectors. cible upon light acceleration after the Install injector tester onto first injector to TCC has just engaged in the range of 35 be tested. Cycle fuel pump, record read- to 42 mph. ing in kPa. Fire injector and immediately note pressure reading. Repeat proce- If the injectors need to be cleaned, there dure for each injector. If there is a differ- are special injector cleaning tools availence of 10 kPa + or - from the average able such as 5-35800 or equivalent.
SECTION 3 SELECTED ECM VOLTAGES AND WIRING DIAGRAMS
Section 3 includes selected ECM circuits and voltages to assist in diagnosis. Use on& a high impedance digital multimeter ( J 34029-A or equivalent) for all ECM tests. For voltages in the engine run column, be sure the vehicle is idling in closed loop with no scan tools installed. You can use the "Service Engine Soon" light to indicate closed loop. JUMPER ALCL A to B; if the light blinks quick (twice a second) you are in open loop. If the light blinks slow (once per second) you are in closed loop.
Diagnostic Products has attemped to make our technical information as accurate as possible. However, with the many changes which are made in production of vehicles you should verify the voltages by being sure that the reading you get from a circuit does in fact reflect the component you are attempting to test. Revisions to this manual and particularly to this section are planned. Your tool dealer will have copies of the revised publication when it becomes available or you can contact Diagnostic Products directly so you can receive this information as soon as it is available.
W2 ECM VOLTAGE IDENTIFICATION CHART
1.8 L "J"TURBO
VOLTAGE
KEY ENG ION I R U N I
10
CIRCUIT
PIN
1 13.4 1 Fuel Pump Relay -
--
NOTE
IN
II
1 KEY 1 ENG
I ON 1 RUN
CIRCUIT Battery 12v lnput
1 ~ 11 -
A2 A3
Not Used Not Used
1 12.4 1 .S
I
,I
VOLTAGE
1 Wastegate --
IA~
-
13.8
Service Engine Soon
13.6
Ign. -- ECM Fuse
A5 A6
TCC Control A/T
b4 ( 5 6 7
(
I
Not Used Reference
11.6
Not Used ESC Sensor Signal
9.1 12.2 0
ALCL -- Serial Data
g A10
Vehicle Speed Sensor -
2.5
MAT, MAP Ground
0
System Ground
0
A1 1 A12
9.1 13.8 0
NotUsed
10 Park Neutral Switch &: 11 Not Used
0 13,7
I ,
I Coolant Fan
1 12.2 1 13.8 1 A/C Relav Control
1 Not Us 1 Not Us 1I Not Us
I
1 ~ 21 5
ldle Air Control --B--Low ldle Air Control - - B - - H ~ Q ~ ldle Air Control --A--High
Not Us
ldle Air Control --A--Low Not Used P/S Pressure Switch Crank Signal Coolant Temperature M A P - s ~ ~ ~ ~
D l 2 Notused
MAT Signal .45
TPS Sensor Signal
4.9
TPS 5v Reference
C13
D l 3 Not Used
C14
~ 1 4Fuel lnjectors 3 & 4
12.2
13.8
~ 1 5NotUsed ~ 1 6Fuel lnjectors 1 & 2
12.2
13.8
--
Not Used
NOTES & SPECIAL INFORMATION [ I ] Fuel pump relay will read 12v tor 2 seconds when lgnttion is M c h e d on. (21 Vonage reading varier. [3] Varies trom .8 w n to battery w n depending upon driK wheel posttion. [4] Varies with ternparalure. (51 Engine running witage will be high or low depending U A/C k on or off. [8] Note voltage change when s h ~ e d Into gear for autoihalIitransrnosaon. [TJ Hdl Effect Senmr. Voltage will be lowwnan vane 1s passing through M c h .
1~15
VOLTAGE TESTING REQUIREMENTS: 1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature. 3) ldle engine in "Closed Loop"for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5 ) No "Scan"tools installed. 6) "Key On' readings represent known good battery.
ECM VOLTAGE IDENTIFICATION CHART
2.OL "J"BODY
VOLTAGE KEY I ENG ~ P E N I RUN CKT. ION
I
1
113.4
On
on 13.8
I
1
I CIRCUIT
I Fuel Pump Relay
12.2
Not Used A/C Relay
I
P'N]NOTE
IAI 1 1 A2
A3
blNI
Ign. -- ECM Fuse
0-3
TCC Control or m/t shift light
A7
ALCL -- Serial Data
A8
Coolant & TPS Ground
~ 1 1 2
4.5
.1
.1
0
System Ground
IAI
CIRCUIT
61 ~2
Battery 12v Input Voltage Monitor
b3 1 b4 1 c;
13.6
HE1 Ground
I
Not Used
I
Distributor Reference
37
Not Used
38
A/C Signal
31 1
Not Used
.45
.1
TPS Sensor Signal
C13
4.9
4.9
.1
TPS 5v Reference
C14
Not Used
C15 C16
13.7
12.1
Battery 12v Input
NOTES & SPECIAL INFORMATION [I]Fuel pump relay will read 12v for 2 seconds when ignition is witched on.
[2] VoRage reading variea [3] V a r b fmm .4!5 vo4i to batlory voh depending upon drhw wheel pamion. [4] Vadea Mth temperature. [5] Engine funning whage will be high or low depending if A/C Is on or off. [B] Note w b g e change when shifted into gear for automatic transmission. Hall EffactSensor. VoRage will be low when vane is passing through witch.
m
0
13.9
0
I
0
l o I 1
1
.8
1 I
I I
I
1 0
I
System Ground
0
1 0
MAP Ground
0
0
EST Bypass Signal
4.5
4.5
0
Oxygen Sensor Ground
.1
.1
0
Oxygen Sensor Signal
.2
.5
0
13.2
12.1
08
Not used
IDl31
Not Used
r-
11.9
12.1
015 lD1 6
.1
Ground
~5 ~6 ! 07
.45
13.7
Not Used
~2 03
C12
11.9
l o I 1
I
ENG OPEN RuN1cK-r.
I
1 ID1 I
Not Used
I I KEY
I
Not Used
2.5
VOLTAGE
I
I
---
N Ou~s e d Fuel Injector Driver
12.3
VOLTAGE TESTING REQUIREMENTS:
1) 2) 3) 4) 5) 6)
This chart is for use with a digital multimeter. Engine must be at operating temperature. Mle engine in "Closed Loop"for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan"tools installed. "Key On" readings represent known good battery.
W4 ECM VOLTAGE IDENTIFICATION CHART
2.8L LB6 "A & J" BODY VOLTAGE
VOLTAGE
NOTE
1 5
7
2
5
3
6
7
4
NOTES & SPECIAL INFORMATION
VOLTAGE TESTING REQUIREMENTS:
( I ] Fuel pump relay will mad 12vfor 2 seconds when ignition is switched on. (21 Voltage reading varies. (31 Var* from .45 volt to battery w k depending upon drive wheel position. (41 Vanes with temperature. 151 Engine funning vokage will be high or low depending if A/C is on or off. [8] Note voltage change when shifted into gear for automatic transmisaton. Hall Effect Sensor. Voltage will b e low when vane IS passing through switch
1) 2) 3) 4) 5) 6)
m
This chart is for use with a digital multimeter. Engine must be at operating temperature. Idle engine in "Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. "Key On" readings represent known good battery.
W5 ECM VOLTAGE IDENTIFICATION CHART
VOLTAGE
2.8 L "F"BODY
VOLTAGE KEY ON
CIRCUIT
NOTE
I
ENG RUN
I
Battery 12v Input
1 1
Voltage Monitor (fuel pump:
HE1 Ground (EST ref low) EST Control Reference Mass Airflow Sensor Not Used 2
5
A/C Signal Power Steering Pr. S/H
3 4
8
Park Neutral Switch
$:-,
Not Used Not Used
D l 2 Not Used 0 ~ 1 3TPS,CTS,MAT Ground 0 12.2 13.8 ~ 1 4Fuel lnjectors 2-4-6
~ 1 5Fuel lnjectors 2-4-6 ~ 1 6Fuel lnjectors 1-3-5 NOTES & SPECIAL INFORMATION [I] Fuel pump relay will read 12v tor 2 recondswhen ignRlon is switched on. [2]Vonage reading mi-. [3]Varier horn .B wll to battery wll depending upon drive wheel portlion. [4]Varies with temperature. [5] Engine tunning wnage Mil be high or low depending If A/C is on or off. [el Note wnage change when shllled into gear for automatic transmimion. [7] Hall EffectSensor. Voltage Mli be low when vane is w i n g through owitch. [a] Mewred between terminals C13 and 013.
12.2 13.8 12.2
13.8
VOLTAGE TESTING REOUIREMENTS: 1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature.
3) 4) 5) 6)
Idle engine in "Closed Loop' for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. "Key On" readings represent known good battery.
W6 ECM VOLTAGE IDENTIFICATION CHART
2.8L "P"FlERO
VOLTAGE KEY ENG ON l R u N
I
CIRCUIT
I
I
VOLTAGE I KEY I ENG I
I
PIN N O T E =IN
CIRCUIT
Not Used Not Used
A3
B3
HE1 Ground (EST ref low) 0
0
EGR Control
-
A4 -.
ESTControl
0
1.3
Service Engine Soon
IA~
B4
Reference
0
1.6
Ign. -- ECM Fuse
1~6
B5 6
1
11.9
I I I
Not Used
I
I
IF37 8
ALCL -- Serial Data
13.7
NotUsed
- .
]
Shift Light M/T
Battery 12v Input
RUN
A1 A2
Fuel Pump Relay
~1 B2
ON
I
Not Used A/C Signal
I
I
TXT On
13.8 n
n 12.2
C I 7~4 ALCL -- Diag. Terminal
MAT Signal
hi21
System Ground
IDA I
Not Used
1 Not ~ s h a b l e 1 ldle Air Control - - A - - ~ i g k5 h 1
I
I
Not Used
c7
Not Used
C8
System Ground
10
10
I
1 EST Bypass Signal 1 0 14.5 I 1~6 1 Oxygen Sensor Ground ( o 10 1 1~~ ( Oxygen Sensor agnal 1 .2 1.5 I 1 ~ 81 EGR Diagnostic s/w ( 12.2 113.8 1 5
2
( Not Used Coolant Temperature MAP Signal -
MAP Signal
~12 TPS, CTS Ground
0
0
TPS Sensor Signal
D l 3 MAT, MAP Ground D l4 Fuel Injectors 1-3-5
0
0
12.2
13.8
D l 5 Fuel Injectors 1-3-5 016 Fuel lnjectors 24-6
12.2
13.8
12.2
13.8
TPS 5v Reference Fuel Injectors 2-4-6 Battery 12v l nput -
-
NOTES & SPEClAL INFORMATION [ I ] Fuel pump relay will read 12vfor 2 seconds when ignition is switched on. [2] Vokage reading v a r i . 131 Vanes from .8 wit to battery wn depending upon drive wheel position. 141 Varies A h temperature. [5] Engine ~ n n l n vdlage g will be high or larr depending If A/C is on or off. [6] Note wnage change whan rhifted into gear for automatic transmission. [7] Hall E f f d Sensor. Voltage Mli be low when vane is passing through switch. [B] Measured betwen terminals C13 and D13.
VOLTAGE TESTING REQUIREMENTS: 1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature.
3) ldle engine in "Closed Loop" for ENG RUN voltages. 4) Diagnostic test terminal in ALCL not grounded. 5) No "Scan" tools installed. 6) "Key On" readings represent known good battery.
W7 ECM VOLTAGE IDENTIFICATION CHART
VOLTAGE
3.OL "N& H" BODY
VOLTAGE
NOTE 1 5
7
2
5
3
8
7
4
-
2
-
Dl D2
Ground
0
0
.1
Coolant Fan Control
12
.1
0
D3 04
Cylinder Select for 6 cyl 11.9
13.7
12.1
D5
EST Bypass Signal
4.5
0
D6 D7
Oxygen Sensor Ground .1
.1
0
D8 D9 Dl0 D l1 D l2
Not Used 4.5
Oxygen Sensor Signal .2 Not Used Not Used Ground
.1
Power Steering Switch 12.0 TPS/CTS/ATS Ground 0
.1 D13 Ground D l4 Fuel lnjector Cy12-4-6 11.9
D l 5 Fuel lnjector Cyl 1-3-5 11.9 D l 6 Fuel Injector Cy12-4-6 11.9 NOTES & SPECIAL INFORMATION
VOLTAGE TESTING REQUIREMENTS:
[ I ] Fuel pump relay will read 12vfor 2 seconds when ignaion is A c h e d on. 121 Voltaae readlna varies. "~ i3j ~ a r i i f r o r n .45 wH to battery voll depending upon drive wheel position. [4] Varia with temperature. [S] Engine Nnning wnage will be high or low depending if A/C is on or off. [a] Note wnage change *en shifted Into gear for aulomallc transmission. Hell Effect Sensor. Voltage will be law when vane is passing through witch. 181 X Body only
2) 3) 4) 5) 6)
m
1) This chart is for use with a digital multimeter.
Engine must be at operating temperature. Idle engine in "Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. 'Key On" readings represent known good battery.
W8 ECM VO .TAGE IDENTIFICATION CHART
3.8L A, C AND H BODY STYLES
OLTAGE
v
NOTE 1
5
7
2
5
3 7
Not Used
C1
Not Used
c2 ~3
.8
.8
0
Idle Air Control --B--Low
10.6
12.3
0
10.6
12.3
0
Idle Air Control --B--High (-4 Idle Air Control --A--High ~5
.8
.8
0
Idle Air Control --A--Low
.1
.1
0
EGR Vacuum Diag. Sw.
.1
I
0
1
2.0 2.5
1 1 1
13.5
(
0
2.2
1
.1
(
0
-
I
4th Gear Switch
IC8
I
Cruise Control
~CS
Coolant Temperature
lCIOl
Manifold Air Temp.
1 ~ 1 1
1 1
I
I
2.0
I
~6 c7
.45
.1
TPS Sensor Signal
4.9
.1
TPS 5v Reference
12.0
13.2
12.1
Fuel Injector, Cyl 2
11.9
13.7
12.1
Battery 12v Input
NOTES & SPECIAL INFORMATION 11 Fuel pump relay will read 12vfor 2 ssconds when ignition is .witched on.
2) VoHage reading h a . 31 V a r i from .45 wH to battery w H depending upon drive wheel position. 4) Varier with temperature.
51 Engine running voHage will k high or low depending If A/C is on or off. 81 Note voltage change when shifted into gear for automatic transmission. 71 Hall Effect Sensor. Voltage wlll be low when vane is passing through witch.
I
-
-
C13 C14 C15 C16
Dl D2 D3 D4 D5 D6 D7 D8 D9 -
Dl 1 Dl2 Dl 3 Dl 4 Dl 5 Dl 6
Ground
0
Coolant Fan Control
12
Cylinder Select for 6 cyl Not Used EST Bypass Signal Oxygen Sensor Ground Oxygen Sensor Signal Not Used Not Used -
Power Steering Switch 12.0 TPS/CTS/ATS Ground 0 TPS/CTS/ATS Ground 0 Fuel Injector, Cyl 1
11.9
Fuel lnjector, Cyl3
11.9
Fuel Injector, Cyl4
11.9
VOLTAGE TESTING REQUIREMENTS:
1) 2) 3) 4) 5) 6)
This chart is for use with a digital multimeter. Engine must be at operating temperature. ldle engine in "Closed Loop"for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan"tools installed. "Key On" readings represent known good battery.
ECM VOLTAGE IDENTIFICATION CHART
3.8L TURBO GRAND NATIONAL "G"BODY VOLTAGE
VOLTAGE
I
KEY ENG CKT. ON lRuN OPEN
CIRCUIT
;;:;1
0
I Fuel Pump Relay
:;:;1
A/C CIutchControl Canister Purge Control EGR control
1
KEY ON
CIRCUIT
+ Battery 12v lnput
A'
3
Crank Reference Low
Service Engine Soon
Crank Reference High
Ign. -- ECM Fuse
Mass Air Flow Sensor
1~2.2 ALCL -- TCC control ALCL -- Serial Data
.1
I ALCL -- Diag. Terminal
A9
Vehicle Speed Sensor
El
Not Used Park Neutral Switch
$-,
11 Not Used 0
bid
Ground
Fuel Injector, Cyl 5
ID1 I Ground lD2 1
Coolant Fan Control Wastegate Controll
1 12 11.9
( .1 13.7
10 12.1
Not Used
lD5 1
EST Bypass Signal
14.5
14.5
10
Oxygen Sensor Signal Not Used EGR Diagnostic S/W Ground Power Steering Switch
12.0
13.2
12.1
Fuel Injector, Cyl 6
.45
.45
.1
TPS Sensor Signal
4.9
4.9
.1
TPS 5v Reference
12.0
13.2
12.1
Fuel Injector, Cyl 2
11.9
13.7
12.1
Battery 12v Input
NOTES & SPECIAL INFORMATION :I] 121 :3] :4] :5] :8] 71
Fuel pump relay will read 12v for 2 sewnds when ignition is switched on. VoHage reading varlea. Varies from .45 volt to battery volt depending upon drive wheel position. Varies A h temperature. Engine running voltage will be high or low depending WA/C Is on or off. Note voltage change when shifted Into gear for automatic transmission. Hall Effect Sensor. Voltage will be low when vane Is p i n g through switch.
c12 C13 C14
TPS/CTS/ATS Ground
C15 C16
Fuel Injector, Cyl 3
Not Used Fuel Injector, Cyl 1
Fuel Injector, Cyl 4 VOLTAGE TESTING REQUIREMENTS: 1) 2) 3) 4) 5) 6)
This chart is for use with a digital multimeter. Engine must be at operating temperature. Idle engine in 'Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan"tools installed. "Key On" readings represent known good battery.
W 10 ECM VOLTAGE IDENTIFICATION CHART
4.3 L "B & G" BODY
VOLTAGE
KEY ION 0
I I ENG RUN 13.4
CIRCUIT Fuel Pump Relay Not Used
1 12.4 1 0
1 Canister Purge Control Not Used
S
.1
13.8
Service Engine Soon
ALCL -- Serial Data
INOTEp"
A1 A2
VOLTAGE
1 KEY I ENG 1
!
I ON I RUN
ClRCUlT
I
Battery 12v lnput
1 ~ 3I A4 A5
I
Not Used ESC Signal
8
1
A/C Signal
122 0
m I
1 4.9
1 4.9
1 ALCL -- Diag. Terminal
1 ~ 9I
b9
.5
.5
Vehicle Speed Sensor
0
0
Coolant & TPS Ground
BlO Park Neutral Switch b111 Not Used
.1
.1
System Ground
A1 0 A1 1 1~12
c12 C13
D l 2 NotUsed
C14 C15 C16
D l 4 Fuel Injector "B" Driver 12.2
Not Used .5
.5
TPS Sensor Signal
4.9
4.9
TPS 5v Reference
12.2
13.7
Fuel Injector "B" Driver
12.2
13.7
Battery 12v Input
NOTES 81SPECIAL INFORMATION ( I ] Fuel pump relay will read 1% for 2 seconds when ignition is switched on. [2]Voltage reading varies. (31 Varies from .8 w i l to banery w i l depending upon drive wheel posttion. [4] Varies wllh temperature. (51 Engine running wilage will be high or low depending If A/C is on or off. (61 Note wltage change whan ~htftedinto gear for automatic transmiasion. (7) Hall Efied Sensor. Voilage will be low when vane is passong through switch.
I
EGR Temp Diag. - s/w .
h121 Not Used
(
13.8 0 I
12.3
113.8
I1
o
PIN ( A ~ - JD
y2.3
13.7
I
I
I
I
I
I
D13 Not Used 13.7
D l 5 Fuel Injector " A Driver 12.2
13.7
D l 6 Fuel Injector "A Driver 12.2
13.7
VOLTAGE TESTING REQUIREMENTS: This chart is for use with a digital multimeter. Engine must be at operating temperature. Idle engine in "Closed Loop"for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan"tools installed. 6) "Key On" readings represent known good battery. 1) 2) 3) 4) 5)
W 11 ECM VOLTAGE IDENTIFICATION CHART
5.OL, 5.71 "F"BODY
VOLTAGE
VOLTAGE
CIRCUIT 12.2
13.8
Air Switch (Port Solenoid) A2
12.2
o
Canister Purge
1 12.2 1 0 .1 12.2 12.2
Service Engine Soon
13.8 I
13.8
1 13.8 2.5
4.3 4.9
1 EGR control
,
4.9
I
(
.
Ign. - -- ECM Fuse Shift Ught M/T TCC ControiA/T
ALCL -- Serial Data ALCL -- Diag. Terminal
11.9
13.7
2
Fuel Pump Signal
0
13.8
63
HE1 Ground (EST ref low) 0
I A ~1
84
b5 I
Not Used Reference
B6
Not Used
87 8 g
ESC Sensor Signal
A5 A6 I
IA~ A8 A9 0
1.6
( Vehicle Speed Sensor
IAI 1
10
10
~AI1 I
10
10
1 MAF Analog Ground 1 System Ground
2
3
1~121
5
6
El 01
10
A/C Signal
On
Off
Not Used Park Neutral Switch
zh,,
11 Not Used
2
0
11.6
9.2
1 1 1 12.2 0
2 : i 3
12 MAF Sensor Input
13.8 0
:3,7
.4 to 1
0
C13 C14 C15 C16
D l 5 Fuel Injectors 1-3-5-7 ~ 1 6Fuel lnjectors 2-4-6-8
12.2
13.8
12.2
13.8
2.1
MAT Signal
c12
.55
.55
TPS Sensor Signal
4.9
4.9
TPS 5v Reference
12.2
13.8
EGR Diagnostic s/w
11.9
13.8
Battery 1% Input
I
9.2
Burn-Off Relay Control 0 DI2 D l 3 Notused D l 4 Notused
2.5
I ] Fuel pump relay will read 12vtor 2 seconds when ignition Is switched on. 21 Vonage madlng varier. 3) Varies from .8 wn to battery wn depending upon d h wheel position. :4] Varier with temperature. :5] Englne wnning wnage wlll be high or low depending if A/C Is on or off. :8] Note wnage change when shined into gear for automatic transmission. 71 Hall Effect Sensor. Vonage will be low when vane is passing through switch. 81 + or - .075V mee~ured betwen C13 and D l 2 91 OVwith circuit closed by a/c high pressure switch.
Battery 1% Input
A3
1.6
NOTES & SPECIAL INFORMATION
1
1
VOLTAGE TESTING REQUIREMENTS: This chart is for use with a digital multimeter. Engine must be at operating temperature. Idle engine in "Closed Loop' for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. 6) "Key On" readings represent known good battery. 1) 2) 3) 4) 5)
W 12 ECM VOLTAGE IDENTIFICATION CHART
VOLTAGE
5.OL LB9 "F"BODY
VOLTAGE
NOTE 1 1
7
2
5
3
6 4
NOTES & SPECIAL INFORMATION
VOLTAGE TESTING REQUIREMENTS:
[ I ] Fuel pump relay will mad 12vfor 2 seconds when ignition is mltched on. [Z] Vohage mading varies. [3] Varies from .45 w h to battery wtl depending upon drive wheel position. [4] Varies with temperature. 151 Engine running whage will be high or low depending If A/C Is on or off. [6] Note whage change when shied into gear for automatic transmission. PI Hall EffectSonsor. Vonage wlll be iow when vane is passing through switch.
1) 2) 3) 4) 5) 6)
This chart is for use with a digital multimeter. Engine must be at operating temperature. Idle engine in "Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. "Key On" readings represent known good battery.
ECM VOLTAGE IDENTIFICATION CHART
5.7L LB9 "Y"CORVETTE
VOLTAGE KEY ENG PEN loN 1RuNfkT.I 0
13.9
0
cmcunA1 Air Switch -- Port Solenoid A2
13.9
12.4
13.8
12.2
Canister Purge Control
12.4
13.8
12.2
EGR Control
-.1
13.8
12.2
Service Engine Soon
13.3
13.6
12.1
Ign. -- ECM Fuse
12.4
13.8 0
M/T Ovedrive or A/T TCC Control
~ALCL-- Serial Data
14.9
.5
.5
0
0
.1
.1
1.1
~ALCL-- Diag. Terminal
.6
Vehicle Speed Sensor MAF Sensor Ground
0
NOTE
Fuel Pump Relay
12.4
14.9
I
Ground
A3 A4 A5 A6
1 KEY I ENG OPEN RUN CKT. ON
I
IN b1
I
VOLTAGE
CIRCUIT
I
--
1 11.9 1
Battery l2v lnput -
-
12.1 0
2
Fuel Pump Signal
0
13.9
3
EST Reference Low
0
0
Distributor Reference
7
0
I~7
1 ~ 81 2 1 ~ 9I A10 3 A1 1 1~12)
0 12.2
5
0
Not Used
C
s11
4
Park Neutral Switch
&:
0
12.3
0 13.7
0 0
NotUsed MAF Sensor Input
2.5
NOTES & SPECIAL INFORMATION
VOLTAGE TESTING REQUIREMENTS:
[I] Fuel pump relay will read 12vfor 2 seconds when ignition is switched on. (21 Voilage reading varies. [3]Varies from .45 van to battery volt depending upon drive wheel position. 141 Varies with temperature. [S] Engine ~ n n i n wnage g will be high or low depending if A/C Is on or off. 161 M e Mitage change when shiftad into gear for automatic transmisrrion. Hall E f f d Sensor. Vonagewill be low when vane is parsing through Jwitch.
1) 2) 3) 4) 5) 6)
m
13.7
.4- 1
This chart is for use with a digital multimeter. Engine must be at operating temperature. Idle engine in "Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No *Scanu tools installed. "Key On" readings represent known good battery.
W 14 ECM VOLTAGE IDENTIFICATION CHART
5.7L "Y"CORVETTE 1985
VOLTAGE
I
I
CIRCUIT
NOTE
Fuel Pump Relay
1
1
112.2
10
1 Canister Purge
1 ~ 3I
I
12.2
1 13.8 1 ,, 2.5
4.3 4.9
4.9
Shin Ught M/T TCC Control AD
ALCL -- Serial Data ALCL -- Diag. Terminal
.6
.6
Vehicle Speed Sensor
0
0
MAF Analog Ground
0
0
I System Ground
A6 1 ~ 7 J
A8 A9
2
5
A10 A1 1
I KEY I
I
IN
ENG I RUN
Battery 12v Input
11.9
13.7
82
Fuel Pump Signal
0
13.8
b3 1
10
HE1 Ground (EST ref low)l 0 -
1
--
--
64
EST Control
0
1.3
B5 ~6
Reference (EST Ref Hi) 0
1.6
B7
ESC Sensor Signal
88 sg
-
Not Used A/C Signal
9.2
9.2
13.8
12.2 o
off On
o
Not Used
10 11 MAF Sensor 12 Not Used
Park Neutral Switch
IAI 2
ON
CIRCUIT
Bl
- -
EGR Control
VOLTAGE
zk
-
I
-
-
0
0
12,3
13,7
2.5
-
.4 to 1
I
2
9 4
8 8
NOTES 8 SPECIAL INFORMATION [ I ] Fuel pump relay will read 12v for 2 seconds when ignition Is witched on. [2] Voitage reading varier. [3] Varies from .6 vok to battery volt depending upon drive wheel position. [4] Varies with temperature. [5] Engine mnning voltage will be high or low depending If A/C is on or off. [6] Note witage change when shifted into gear tor automatic transm~ssion. [7] Hall E f f d Sensor. Voltage will be low when vane is passing through switch. [8] + or .075V measured between C13 and D l 2 [Bl OV with c~rcultclosed by a/c h ~ g hpressure svntch.
-
VOLTAGE TESTING REQUIREMENTS:
1) This chart is for use with a digital multimeter. 2) Engine must be at operating temperature.
3) 4) 5) 6)
Idle engine in "Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. "Key On" readings represent known good battery.
W 15 ECM VOLTAGE IDENTIFICATION CHART
2.5 L S I T TRUCK M VAN
VOLTAGE
VOLTAGE
NOTE 1 1
3.5
1.2
2.5
2.2
.45
.45
4.9
4.9
11.9
13.7
(211 Manifold Air Temp Sensor C12 C13 TPS Sensor Signal C14 TPS 5v Reference C15 Not Used C16 Battery 12v Input
2
5
3
8
MAP Sensor Signal
NOTES & SPECIAL INFORMATION [ I ] Fuel pump relay will read 12vfor 2 seconds when ignition is switched on. [2] Voltage reading varies. [3] Varies from .45 volt to batiery wH depending upon driva wheel position. [4] Vatim with temperature. [SJEnglne ~ n n l n voltage g will be high or low dependlno If AIC Is on or off. [6] ~ o i voltage e change when shntez Into gear for aulo~atlc'transmission. [7] Hall Ened Senaor. Voltage will be low when vane Is passing through switch.
Dl2 ~ 1 ~ 1 015 DI 6
Not Used NotUsed 3 Not Used 4 Not Used Fuel Injector "A" Driver 12.2
13.7
VOLTAGE TESTING REQUIREMENTS: 1) This chart is for use with a digital multimeter.
2) 3) 4) 5) 6)
Engine must be at operating temperature. Idle engine in "Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. "Key On" readings represent known good battery.
W 16 ECM VOLTAGE IDENTIFICATION CHART
4.3L, 5.OL, 5.7L, 7.4L TRUCK
VOLTAGE KEY ION 0
I I ENG RUN 13.4
CIRCUIT
CIRCUIT
NOTE
Fuel Pump Relay
A1
Not Used
A2
VOLTAGE
1
Not Used
- -
-
2
Voltage Monitor (fuel pump)
3
HE1 Ground (EST ref low) 0
0
13.9
0
12.4
1;1 1 1 13.3 1 13.6 12.2
4.9
(
1 TCC
( 13.8
; :1 1
1 ~ 6I
Ign. -- ECM Fuse
Control or M/T shift light
.5i:i
ALCL -- Serial Data
4.9
ALCL -- Diag. Terminal Vehicle S ~ e e d Sensor
1o .1
1o
-
.1
-
-
-
[MAT &TPS Ground
IAI i l 1~12
Not Used
c12 C13 C14
.45
TPS Sensor Signal
4.9
4.9
TPS 5v Reference Not Used
13.7
A10
System Ground
.45
11.9
-
IA~
Battery 12v Input
10 Park Neutral Switch 11 Not Used b121 Not Used
2; ,,
0
12,3
I
C15 C16
NOTES & SPECIAL INFORMATION
VOLTAGE TESTING REQUIREMENTS:
[I] 12v for 2 reconds on 4.3 & 5.0 Land 20 seconds for 5.7 & 7.4 L [2] Voltage reading varies. [3]Varies from .45wll to baliery voh depending upon drive whwl position. [4] Varies with temperature. [5] Voiiage measured between C13 and A1 1 (+ or - .05 V) [6]Note voltage change when shmed into gear for aulomatic transmission. Also, darmshM control on THM 400. [7] Except 4.3 L M & G van. this system is wired at opposlte ends. [B] Nd used on 7.4L
1) 2) 3) 4) 5) 6)
This chart is for use with a digital multimeter. Engine must be at operating temperature. Idle engine in "Closed Loop" for ENG RUN voltages. Diagnostic test terminal in ALCL not grounded. No "Scan" tools installed. "Key On" readings represent known good battery.
3.8L "C& H" BODY TWROTTLE
POSITION SENSOR
OXYGEN SENSOR CR(3UND
-5s
nm n o w
VMCLE
-u
VE-E WEED
SPEED
-
LCM FLn€
I
-
SENSOR
I
-
ru-c
a+
LINK
MTTERY
'=L
--
-
KIN. SWITCH CRANKIRUN
m m w o Pi
CONSTANT BATTERY MLTACC
mi
3
PARK
CYLI-R YLCCT 6 CYLMER
GROUND
CIH
5w.
RUN
-mnz
A I C
FMI EDR CANISTER P V RCONTROL RELAY CC
A I C RELAY L5 C M A F TCC POWER STCEWNa
PR
stw
F U n PUMP C 3 NJCCTOR
I SWTCHEO #-I-
7 R/C DRSH SWITCH
rI
R/C OH S I G M L
F-.J$
P O K R STEERING PRESSURE SWITCH
3.8L "C& H" BODY
t I
POWER SlEERW3 PRESSURE SIW
ECN FUSE
R/C CLUTCH COMROL
,
;En*
E6R DIRGHOSTIC SWITCH E6R COHTROL S U I T C H CRHISTER PURGE URLUE
"SERUICE EHGIHE
"SERUICE EHGIHE SOOH- L I G H T
GAUGES FUSE IGH
T
7 R
BR8KE SWITCH
3RD 6ERR S V I T C H TCC COHTROL
D 87
I
-
I
4 T H GERR
I
CRH SIGHRL
IGHITIoH
I : : : CONTROL
FRH CONTROL
ECM @ "C" CRR W I L L USE RESISTOR. JUMPER WIRE W I L L BE USED
!
TRRHSllISSIOH 4TH GERR SWITCH
% -I .
-
HIGH PRESSURE SWITCH COWRESSOR CASE GROUtQ
E C FUSE ~
ECM
MAGNETIC PICKUP & IGNITION MODULE
EST REFERENCE BYPASS GROUND
IAC VALVE IAC COlL "A" HI IAC COlL "A" LO IAC COlL "B" HI IAC COlL "B" LO
OXYGEN SENSOR SIGNAL
OXYGEN SENSOR GROUND
ENGINE GROUND
INJECTOR DRIVE
INJECTOR DRIVE
EGR DIAGNOSTIC TEMP. SWITCH
PARK NEUTRAL SWITCH (A/T)
VEHICLE SPEED SENSOR A/C SIGNAL
5.0LITRE
1
GAGES FUSE
ECM
SERVICE ENGINE SOON LIGHT CONTROL DRIVER
IGN. 12 V.
A5 S.E.S. LAMP
A
BRAKE SWITCH
B
AUTOMATIC TRANSMISSION TCC SOLENOID
A
B
TCC CONTROL A/T
A7
c
rn D
I
I
FIEJDCIBIA
EGR SOLENOID
EGR CONTROL
A4
&
d CANISTER PURGE SOLENOID
CANSITER PURGE
A3 (GRAY CONN.)
c2
AIR CONTROL SOL.
DIVERT SOLENOID P
(BLACK CONN.)
AIR SWITCH SOLENOID
PORT SOLENOID
-
A2
1
I
,
FIEIDCIBIA 1 I I
,
FAN
CONTROL RELAY E
B+
-
D
-
FAN B+
C
-
FUSE
COOLING FAN CONTROL
c1
B
A
COOLING
\
1 -
ECM
I
FAN
ECM DIAGNOSTIC TEST SERIAL DATA
SYSTEM GROUND SYSTEM GROUND SYSTEM GROUND
COOLING FAN REQUEST, HIGH A/C PRESSURE
MAT SIGNAL
5 V. REFERENCE
TPS SIGNAL 5V. RETURN
COOLANT TEMP SENSOR SIGNAL
5.0LITRE ECM
FUSE & HOLDER ----- -I
12 VOLT 12 VOLT FUEL PUMP RELAY DRIVER ( + 12 VOLT)
A1
SYSTEM GROUND
A12
PUMP FUEL PUMP VOLTAGE MONITOR
I
MAF SENSOR
POWER R E L T
SYSTEM GROUND
~1
ANALOG GROUND
~ 1 1
MAF SIGNAL
BURN-OFF CONTROL
-
I ENGINE GROUND
FUEL
iA 9 4 , B -C
-
OIL PRESSURE SWITCH
E
MAF SENSOR BURN-OFF RE LAY
A must book
technician or This book will take you from easily understoodI basic electrical theory t6 microcomputer engine control. A concept in automotive technology is explained. It will introduce you to the new techniques and took which will enable you to diagnose and fix today's automobiles.
rE-~.s.
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the veer,
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a v t r a r n m h WDII ~ w r ~ m n
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Brock Yates Car & Driver Magazine' -
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You will learn how to: Use Ohm's Law for diagnosis Determine electical failures Access ECM codes Use swners reliably ~se~wiring harness adapters to pinpoint open & short c i r ~ i t s
t-xTMs - ook is for:
for your audi improve and profession.
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What n t h m r e a r m e a v i n m m :A
UWI;W~U I W I # ;
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Dr. Dawn Lee ~ e f i e l d Texas A&M University
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Definitelythe best available text onthe -subject for my students. ': -1
7. -
AuWmtW Enthysiasts AutomatSve Technology Students ProfessionalAutomotive Technicians
If
Rick Maldonado
v!
Alief-Hastings High School,H w , T& -
+
This book is your reference on GM-andBosch technology Electrical & electronic sensors, wiring, ECM operation, diagnostic procedures and :. $. proper repair procedures are explained.
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-
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Written by a former GM instructor who has taught over 7,000 professional techjcians. This stepby-step guide is quick to read and easv to a~ohr. L.
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