07 Electric Sysetem LG958L

LG958L Training Material Chapter X Electric System Tuesday, May 19, 2015

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RELIABILITY IN ACTION

CONTENTS Structure, Characteristics, and Circuit Diagram Analysis of Electric System Power Supply and Starter System Instrumentation and monitoring system Automatic leveling of bucket Lighting Backup warning system Wiper and washer Electric horn Spare socket

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Section I Composition, Structural Characteristics, and Circuit Diagram Analysis of Electric System of Loader The electric system is an important

part of the loader and is mainly

functioned for start and control of diesel engine and fulfillment of the operations

including

lighting,

signal indicators, and instrument

monitoring. The quality of electric system

directly

influences

the

working reliability and the traveling and operation safety of the loader.

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I. Main Composition of LG958L Electric System

The electric system of loader is mainly composed of the following 5 parts: 1. Power part: Including the battery and alternator assembly.

2. Start part: Mainly including starter, starter relay, and electric lock, which are functioned to start the diesel engine.

3. Lighting and signaling part: Mainly including all kinds of lighting and signal lamps and horns and buzzers, which are functioned to ensure the safety of human and machine and the successful implementation of operations under all kinds of operation conditions.

4. Instrument monitoring part: Including pressure gauges, pressure sensors, temperature gauges, temperature sensors, and low pressure alarms.

5. Control part: Engine control unit and transmission control unit (detailed in the engine system and transmission system). 6. Accessory part: Including the electric wiper, heater, and A/C system.

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II. Characteristics of Electric System of LG958L Loader 1. Low voltage: The rated voltage for electric system of the LG958L loader is 24V powered by two 12 batteries in series connection. 2. DC The diesel engine is started by the starter motor. The starter motor is a DC series excitation motor that must be powered by battery. Therefore, the DC current must be used to charge the battery, which determines that the electric system of the loader is a DC system. 3. Single-wire system All electric devices are in series connection, namely only one wire is connected from the positive post of power supply to the switch and the electric devices and the metal bodies such as the loader frame, diesel engine block, transmission, and torque converter are functioned as the public “grounding wire”. When the single-wire system is adopted, the wire that connected to the metal body is referred to as “grounding wire”. The connection between the negative post of battery and metal body (such as frame) is referred to as “negative grounding” and the connection between positive post and metal body is referred to as “positive grounding”.

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III. Circuit Diagram and Malfunction Analysis Method of Construction Machinery

Expressing method of loader circuit diagram: The circuit diagram is a integral body in which the power supply, starter system, lighting, instruments, and accessories are connected by switches, wires, and fuses as per the corresponding working characteristics and mutual internal relationship. 1) Expressing method for circuit diagram of loader The expressing methods include circuit diagram, schematic diagram, harness diagram, and distribution diagram of electric units. 2) Circuit analysis Abiding principles of circuits: 1. Single-wire system 2. All electric devices are in parallel connection and are controlled by corresponding switches. 3. Low voltage. All electric devices adopt 24V design (the output voltage of alternator is 28V). 4. Negative grounding of battery.

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IV. Circuit Principles to be Borne in Mind

Every complete circuit is composed of power supply, fuse, switch, control device, electric device, and wires. The flow direction of the current must start from the positive post of power supply, reach the electric device through fuse, switch, control device, and wires, and then return to negative post of power supply through wire (or grounding wire) to form the circuit. Therefore, there are three thoughts for reading the electric circuits:

Thought 1: Along the flow direction of the circuit current, start from the positive post of the power supply, check the electric device, switch, and control device, and return to negative post of power supply. Thought 2: Against the flow direction of circuit diagram, start from negative post of power supply (earthing) and return to positive post of power supply through electric device, switch, and control device.

Thought 3: Start from electric device, check the control switch, wires, and control unit, and finally reach the positive post of power supply and grounding wire (or negative post of power supply).

During the actual application, choose different thoughts depending on specific circuit. However, please pay attention to this point that, following the extensive application of the electric control technology, most of the electric device circuits incorporate the main circuit and control circuit. Therefore, both circuits shall be taken into consideration while reading the diagram. 8


Circuit diagram of LG958 electric system

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Section II Power Supply and Starter System

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Power circuits of engine and transmission

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I. Battery (6-QW-120B) The overall machine adopts 2 batteries in series connection. The battery is one invertible DC power supply and is parallel connected with alternator to power the electric devices. A single battery can supply 200A~600A start current to the starter motor within a short period (5~10s). The battery is also equivalent to a large capacitor, which can absorb the over-voltage that may occur any time in the circuit, in order to protect the electric devices against puncture. Caution: The battery must be securely and reliably installed, in order to prevent damage due to bumps during traveling of the machine. Please turn off the power switch when the machine is to be parked for a long time. Warning: Please keep open fire away from the battery. Before the welding operations, please disconnect all connecting wires of the battery, in order to prevent explosion.

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1. Installation location of battery


2. Structure and color change of charge indicator

1 – Green 2 – Black 3 – Light yellow 4 – Battery cap 5 – Observation window 6 – Optic charge indicator 7 – Green small ball Color of charge indicator

Electric quantity The electric quantity is above 65% and the battery is normal The electric quantity is less than 65% and the charging is required.

The battery is over-charged and shall be replaced with new one.

Figure 10-1 Structure and color of charge indicator

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2. Structure and color change of charge indicator The electric quantity of the battery can be understood via the color change of charge indicator (also referred to as charge indication densimeter). Green – Normal, black – to be charged, light-up (or white) – depleted.

When the machine can’t be started, firstly please check the electric quantity of the battery and check the battery cables for reliable connections.

Caution: While frequently checking the battery cable connections and connecting points for reliable connections, please firstly disconnect the negative post of power supply. At the time of assembly, firstly assemble the positive post of battery and then assemble the negative post. At the time of disassembly, firstly disassemble the negative post and then disassemble the positive post. This is intended to prevent the short-circuit from damaging the battery posts and wrenches. Check method for terminal voltage of battery: Check with DC 200V measuring range of multimeter. Connect the red probe to the output cable end of the positive post of battery and connect the black probe to the negative post of the battery. The reading of the multimeter is the terminal voltage of the battery (generally at 24V~26V). 15


II. Power switch

Figure 10-2 Power switch

Power switch (K01K18-A, also referred to as negative switch):

The power switch controls the connection and disconnection between battery negative post and frame (grounding). Turn on the power switch to connect the negative post of battery with frame. Turn on the electric lock to power on the electric loads of overall machine. Turn off the power switch to cut off the negative post of battery from frame so that no loop is formed in the circuits of the overall machine. Even when the electric lock is turned on, the overall machine can’t be powered on nor started. The installation location of the power switch is shown in Figure 10-2. Operations of power switch: “○” is turn-off position and “∣” is turn-on position.

Warning: When the loader is parked for a long time, please ensure to turn off the power switch, in order to prevent electric leakage and other accidents. Before connecting the battery cables, re-tightening the battery cables, or disconnecting the connecting wires of battery, please make sure to turn off this switch for the purpose of safety. 16


III. Alternator

3.1 Working principle of alternator

The schematic diagram of alternator is shown in Figure 10-3. The alternator is composed of rotor, stator, drive pulley, fan, front and rear end caps, and electric brush. The excitation winding is generally wound on the rotor and the stator adopts Y-shaped connection mode. The rectifier is generally a 6-tube bridge full wave rectifier.

1. When a DC voltage is applied on two ends of excitation winding, the current will generate a magnetic field. Driven by the engine, the magnetic field rotates along with the rotor and the three-phase symmetric winding of the stator will, under the application of rotating magnetic field, generate three-phase sine electromotive force with same frequency and same amplitude in spacing of 120º. 17


2. The unidirectional conduction performance of silicone diode is utilized for rectification. At any moment, only the positive diode connected with the winding of the phase with highest potential is on. In same way, the negative diode connected with the winding of the phase with lowest potential is on. Through the sequential turn-on of six diodes repeatedly, one relatively stable pulsed DC voltage is obtained at two sides of the load. 3. The terminal voltage of alternator is proportional to the speed of the alternator. Due to high speed variation range of the engine, the terminal voltage of alternator will also vary within a high range and the output of terminal voltage can't meet the operation requirements of the loader’s electric devices for constant voltage. Therefore, the voltage regulator must be set.

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Figure 10-3 Schematic diagram of alternator

4. The voltage regulator utilizes the on/off of switching tube to change the size of excitation current so as to change the intensity of magnetic field to stabilize the voltage of the alternator. 5. The filter capacitor is mainly functioned to filter away the peak pulse and high frequency interference issued by the alternator. 19


3.2 Wiring method of alternator

Figure 10-4 Alternator

The alternator is generally an assorted part of diesel engine and has three lead terminals, as shown in the Figure 10-4, which are respectively: B+: Alternator power output terminal D+: Charging indicator signal W+: Phase output terminal, which can be functioned as timer signal as well as speedometer signal. The alternator is in parallel connection with battery set to power the electric devices of whole loader. The electric devices are powered by the battery before the start of the loader and are powered by the alternator after the start of loader. At the same time, the alternator also charges the battery set.

Warning: It’s strictly prohibited for the alternator to independently power the electric devices without the battery.

Warning: It’s prohibited to check the power generation of alternator by instantly short-circuiting the positive and negative posts of alternator for generation of spark, in order to prevent burning the diode and impairing the regulator. 20


3.3 Judgment method for normal power generation of alternator and treatment

1. Check with DC 200V measuring range of multimeter. Turn on the electric lock, measure the terminal voltage of alternator (connect red probe to terminal D+ of alternator and connect black probe to grounding), and record the reading of multimeter (This reading is actually the terminal voltage of battery and is generally less than 26V). Start the machine, measure the terminal voltage of alternator again, and record the reading of multimeter (If the alternator is generating power normally, this reading shall be approximate 28V). 2. Treatment

If the alternator fails to generate power or the voltage generated is too low, firstly check the drive belt of alternator for looseness. Turn off the electric lock and use wrench to check the wiring terminals of alternator for correct, tightened, and reliable connections. In addition, check the alternator for reliable grounding.

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IV. Starter system

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IV. Composition of starter system

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I. Structure of starter motor The starter motor is an assorted unit of diesel engine. It is mainly composed of electromagnetic switch, DC motor, shifting fork, and drive gear. The starter motor converts the electric energy of the battery to mechanical energy through DC motor and drives the engine flywheel through drive gear to realize the start of Figure 10-5 Exterior view of starter motor engine. Warning: After the engine is started, immediately release the starter switch, or it will lead to damage of drive gears, burnout of DC motor, damage of flameout electromagnet, and serious impairment of service life of the battery. Caution: Please frequently check the wirings of contacts and terminals for reliable connections. Before the checking, make sure to disconnect the negative post of power supply, or it will probably generate short-circuit spark and damage the wrench and wiring posts. 24


2. Internal structure of starter motor

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Figure 10-6 Internal structure and principle description of starter motor


3. Working principle of starter motor

When the power switch is turned on, the 24V terminal voltage of the battery is applied onto the starter motor via the contact of starter relay. At the moment when the electric lock is rotated to position “START”, two coils of the electromagnetic switch of the starter motor are powered and actuated. The electromagnetic resultant force generated by above two coils drives the movement of movable contact disc so that two contacts of the electromagnetic switch are engaged and the current is inputted to the DC motor coil from the battery for form the circuit via the housing of starter motor. In such case, the DC motor starts the rotation. At the same time, the iron core moves to drive the shifting fork to engage the drive gear with the engine flywheel gear ring. The DC motor drives the rotation of the flywheel and the engine start is initiated.

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During the start process (within more than 10s when the electric lock is rotated to position “START”), the 1# wire is constantly live (24V) and the contacts 1# and 2# are

constantly engaged. As the contact voltage is 24V, the voltage is equal between two terminals of the pull-in coil and no current is flowing. In such case, the iron core is maintained at start status under the action of the electromagnetic force of the holding

coil. When the driver release the electric lock key after the successful start of the engine, the electric lock automatically returns to position “ON” and the 1# wire is

powered off immediately. Within a really short period, the flow direction of the current is contact 1# - contact 2# - pull-in coil – terminal S – holding coil, and grounding. It can be seen that the current flow direction is opposite between the holding coil and pull-in

coil. As the magnetic fields generated are in opposite directions, the electromagnetic

forces applied onto the iron core are cancelled out with each other and the iron core

returns to initial position under the action of spring force. In such case, the contacts 1# and 2# are disengaged, no current flows through the pull-in coil and holding coil, and the driver gear resets to initial position. The starter motor stops working. 27


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4. Judgment for common malfunctions of starter motor: 1) Malfunction symptom: The starter motor runs automatically after the negative switch is turned on.

Cause analysis: This symptom is generally caused by the ablated contacts of starter relay, electric lock, or electromagnetic switch.

Treatment: Re-grind the contacts and movable contact disc or replace electromagnetic switch or starter motor. 2) Malfunction symptom: No reaction of starter motor at the time of start.

Treatment: While rotating the electric lock to position “START”, check the wire voltage at the electromagnetic switch of pneumatic motor. If no voltage is detected, check the electric lock, starter relay, and battery (For instance, check the battery set connecting circuit, negative switch, and grounding wire for reliable connections), or it can be determined as the malfunction of starter motor that leads to start failure.

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Starter switch

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Battery relay

Back

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Transmission control unit (ECU)

Engine control unit (ECU)

Back

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Electric pump

Back

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Section III Instrumentation and monitoring system

1. Circuit diagram of instrumentation system The instrumentation system includes the instrument panel assembly, sensor, and alarm pressure switch, of which the schematic diagram is shown in Figure 3-1. Fuel gauge

Left turn lamp

Working hourmeter

Low engine oil High beam pressure Emergency indicator warning lamp turn lamp

Vehicle speed Braking air pressure gauge gauge

Torque converter oil temperature gauge

Strainer Preheating Handbrake Charging indicator warning lamp indicator indicator

Engine water temperature gauge

Low air pressure warning lamp

Transmission oil pressure gauge

Instrument panel

Power Power case cutoff lamp working lamp Right turn lamp

Low pressure alarm

Emergency turn alarm

Braking pressure sensor

Flasher

Parking brake indicator switch

Engine oil pressure switch

Engine water temperature sensor

Torque converter oil temperature sensor

Fuel level sensor

Strainer warning switch

Figure 10-7: Schematic diagram of instrumentation and alarm system

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37


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2. Sensors

2.1 Temperature Sensor

LG958L is fitted with two temperature sensors to monitor the torque converter oil temperature and engine water temperature. The temperature sensor is equivalent to a thermistor, of which the resistance is reduced along with the increasing of temperature. (226Ohm at 26ºC ambient temperature and 26.4Ohm at 115ºC)

Figure 10-9 Exterior view of temperature sensor

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Figure 10-10 Torque converter oil temperature sensor


2.2 Braking air pressure sensor

Figure 10-11 Internal structure of braking air pressure sensor

The swing of the instrument pointer is achieved by the change of current arising from the slide of resistor pointer within the sensor, which is caused by the deformation of beryllium bronze diaphragm due to change of pressure, as shown in Figure 10-11. 2.3 Fuel level sensor

The fuel level sensor is actually a discrete slide resistor, of which the resistance is reduced along with the increasing of fuel level. It’s installed on the fuel tank. 40


2.5 Alarm pressure switch The overall machine is fitted with two pressure switches, namely low braking pressure alarm switch and low engine oil pressure alarm switch. The specific installation positions are shown in Figure 10-13 and Figure 10-14 respectively. The alarm indicator will alarm when the braking air pressure is less than 0.45MPa or the engine oil pressure is less than 0.08MPa.

Figure 10-13 Low braking pressure alarm switch

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Figure 10-14 Engine oil pressure alarm switch RELIABILITY IN ACTION

3. Examples for troubleshooting of common malfunctions of instrumentation and monitoring system 3.1 Abnormal indication of temperature gauge

Disassemble the sensing wire from the temperature sensor (the torque converter oil temperature gauge and the water temperature gauge correspond to wire 15# and wire 14# respectively). If the instrument indicates full measuring range when the sensing wire is grounded and indicates minimum reading when the sensing wire is hung in the air, it indicates that the instrument and circuit are normal and the sensor is damaged. Replace the sensor. Otherwise, check the circuit. If the circuit is normal, the instrument is malfunctioned. 3.2 Abnormal fuel level indication

Disassemble the sensing wire (wire 19#) from the fuel level sensor. If the instrument indicates full measuring range when the sensing wire is grounded and indicates minimum reading when the sensing wire is hung in the air, it indicates that the instrument and circuit are normal and the sensor is damaged. Replace the sensor. Otherwise, check the circuit. If the circuit is normal, the instrument is malfunctioned.

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Section IV Automatic Resetting System of Bucket

1. Schematic diagram The schematic diagram is shown in Figure 10-15.

Floating solenoid valve Bucket solenoid valve Boom solenoid valve Brown

Load

Blue

Black

Brown

Blue

Black

Normally closed (N.C.)

Proximity switch (boom)

Proximity switch (bucket) Blue Brown Black

Figure 10-15: Schematic diagram for circuit of automatic resetting system 43


1.1 Bucket leveling limiter:

Figure 10-16 Bucket retraction rod and proximity switch

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This device is composed of proximity switch installed on the bucket cylinder bracket (as shown in Figure 10-16) and solenoid valve on the pilot valve. There is a red indicator on the proximity switch, which indicates the status of the proximity switch. When the retraction rod is misplaced from the proximity switch, the proximity switch is turned off, the red indicator goes off, and there is no output signal in the black output wire. If the driver pulls the bucket operating lever to the most rearward position when there is no unloading angle for the bucket, the magnetic circuit is turned on so that the electromagnetic field force generated by the solenoid coil will hold the bucket operating lever (in such case, the driver may release the operating lever and the bucket operating lever will not return to neutral position) and the bucket will keep retracting, till the proximity switch approaches the retraction rod. In such case, the proximity switch is turned on, the red indicator lights up, the solenoid coil is turned off, and the magnetic force disappears so that the bucket operating lever automatically returns to neutral position under the action of spring force and the bucket stops at leveling position.


1.2 Boom floating device

This device does not incorporate the proximity switch and only incorporates a boom floating coil that is located on the pilot valve. After the electric lock is turned on, the coil is powered on constantly. When the driver pushes the operating lever to most forward position, the magnetic circuit is turned on so that the electromagnetic field force generated by the solenoid coil will hold the boom operating lever (in such case, the driver may release the operating lever and the boom operating lever will not return to neutral position) and the pilot valve connects the oil lines of rodless and rod chambers of boom cylinder with the oil pipes by controlling the distributor valve. In such case, the pressure is zero for both rodless and rod chambers and the pressure difference is also zero. If the driver pushes the boom operating lever to floating position during the loading operations, the bucket will fluctuate along with the ups and downs of the ground. If the driver pushes the boom operating lever to floating position to operate the lowering of boom, the boom will lower at fastest speed under the action of dead weight, in order to improve the working efficiency.

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1.3 Troubleshooting of system malfunctions ● Check 10A fuse for burnout.

● Check all connectors for good connections.

● Check gap between metal body and proximity switch (generally no more than 8~10mm).

● Check proximity switch for damage: Turn on the electric lock. The red indicator shall light up when the metal body approaches (When measured with multimeter, the black output wire shall be connected to ground).

● Check the pilot coil: The resistance is approximate 100~200Ohm for three pilot coils.

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Section V Lighting System

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1. Circuit of front combination lamp

1.1 Schematic diagram for circuit of front combination lamp Combination switch

Terminal GreenBrownYellow Red Black Grey Blue Orange White Position Off Left turn Right turn

Backlight

(headlamp low beam)

Left combination lamp Right combination lamp

Left combination lamp

(headlamp high beam)

Warning lamp switch

H ea High dl beam am Low p beam

Terminal Position

Overtaking lamp

Off

Right rear lamp Left rear lamp Gr ee n

Br ow n

Ye R lo e w d

Bl ac k

Gr ey

Bl ue

O ra ng e

W hi te

R es er ve d

Figure 10-18: Schematic diagram for circuit of front combination lamp, turn lamp, and warning lamp

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1.2 Principle description When the electric lock is turned on, the 10A headlamp fuse within the 20-circuit fuse case is turned on (24V) to turn on the combination switch via wire 44# and turn on the contact of high beam/low beam relay of front combination lamp via wire 35#. When the combination switch is not turned on, the wire 49# and wire 50# are not turned on and both left and right headlamps are not working. When the combination switch is at high beam or low beam position, the wire 49# or 50# is turned on (24V) and the coil of high beam/low beam relay of front combination lamp is turned on and actuated so that high beam or low beam of front combination lamp is turned on (24V) and left and right headlamps work at corresponding position.

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1.3 Troubleshooting of common malfunctions of system – Lighting failure of headlamp 1.3.1 Check the bulbs for blackening. If yes, it can be determined that the bulbs are damaged. Replace the bulbs. 1.3.2 Unplug the connector, shift the dimmer switch to high beam position and low beam position respectively, and measure the voltage between wire 49# and wire 50# at the connector with DC voltage measuring range of multimeter. If the voltage is 24V, check the connector for reliable connection. If the connection is loose, re-connect. If the connection is secure, the internal wire of headlamp is loose or the bulb is damaged. If the voltage is 0V, check as below. 1.3.3 Check the 10A headlamp fuse for burnout. 1.3.4 Check the connectors for reliable connections and check the harnesses for wear. 1.3.5 Check the functions of dimmer switch positions as per the Accessories – Combination Switches. 50


2. Circuits of working lamp, rear lighting lamp, and interior lamp Rocker switch of rear lighting lamp (high beam and low beam) Terminal Position

Rear lighting lamp

Rear lighting lamp

OFF

Figure 10-19: Schematic diagram of rear lighting lamp

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Rocker switch of headlamp

Rocker switch of rear illuminator

Terminal

Terminal

Position

Headlamp

OFF

Position

Headlamp

OFF

Figure 10-20 Schematic diagram for headlamps and rear illuminators

2.1 Four lamps on the top front and rear of the cab are defined as headlamp and rear illuminator, two lamps on the rear hood are defined as rear lighting lamp. The switch of interior lamp is attached. Refer to Accessories – Rocker Switches for details of switches of rear lighting lamps and working lamps. 2.2 Schematic diagram: As shown in Figure 10-19 and Figure 10-20. 2.3 The basic principle and the troubleshooting of system malfunction are basic same with the headlamp circuit and are omitted herein.

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3. Circuit of turn lamps: 3.1

Schematic diagram: As shown in Figure 10-18.

3.2.1

The actual combination switch and installation position are shown in Figure 54 and Figure 5-5 respectively. The turn lamp switch is realized by partial function of the combination lamp and the wire colors of three pins used are grey, yellow, and white, of which the grey wire is connected to turn flasher power supply (wire 33#), the yellow wire is connected to left turn signal wire (wire 6#), and the white wire is connected to right turn signal wire (wire 7#).

3.2

Introduction of main units:

Figure 10-21 Combination switch

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Figure 10-22 Installation position of combination switch


3.2.2 Flasher relay (SG252): Three pins of the flasher are defined as below: B – power terminal, connected to wire 21#; L – Flasher signal output terminal, connected to wire 33#; E – Grounding, connected to wire 0#. During normal working, the flasher relay will issue slight “rattle” sound at a frequency of approximate 50 cycles/min. Otherwise, it can be determined that the flasher relay is damaged.

3.2.3 Warning lamp switch: The parking lamp switch controls four turn lamps and two turn indicators on the instrument panel. When this switch is turned on, four turn lamps and two turn indicators flash at the same time to alert the vehicles crossing by.

●

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The basic principle and the troubleshooting of system malfunction are basic same with the headlamp circuit and are omitted herein.


4. Circuit of clearance lamp: 4.1 Schematic diagram: As shown in Figure 10-23. Right combination lamp

OF F

P o si ti o n

T e rm in al

Rocker switch of backlight

Right rear lamp

Left rear lamp

Left combination lamp

Figure 10-23: Schematic diagram for circuit of clearance lamp 55


Figure 10-24: Combination headlamp – Left

Figure 10-25: Left rear tail lamp

4.2 The installation positions of the clearance lamps are shown in Figure 10-24 and Figure 10-25.

4.3 The basic principle and the troubleshooting of system malfunction are basic same with the headlamp circuit and are omitted herein.

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57


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5. Brake lamp circuit: 5.1 Schematic diagram: As shown in Figure 10-26. To ECU case

Intermediate relay (power cutoff)

Intermediate relay Intermediate relay (start interlock) (backup)

Parking brake indicator switch

To starter relay signal terminal

To backup lamp

To terminal G2 of starter switch

Brake switch (left) To instrument panel ECU case indicator To brake lamp Brake switch (right)

Figure 10-26: Schematic diagram for circuit of brake lamp

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5.2 Principle description:

When the brake pedal is depressed, the braking air pressure at the brake lamp switch engages the contact of brake lamp switch so that the current flows to brake lamp through 10A fuse, wire 57# at brake lamp fuse, brake lamp switch, and wire 8# to light up the brake lamp. 5.3 Brake lamp switch: The switch adopts normally open contact, which acts and engages at approximate 1.3bar.

Troubleshooting – How to judge the damage of brake lamp switch: Firstly determine whether the braking pressure is normal (turn on the electric lock. If the low service braking pressure alarm lamp on the instrument panel is off, it indicates that the braking pressure is normal. Otherwise, start the engine, till the low service braking pressure alarm lamp is off). If normal, unplug the wire at the brake lamp switch and measure two pins of the switch with 200Ohm measuring range of multimeter. If the measurement differs from the table below, it indicates that the pressure switch is damaged and shall be replaced.

Brake pedal is not depressed Brake pedal is depressed

OFF ON

Figure 10-27: Installation position of brake lamp switch

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Section VI Backup Warning System Right rear lamp

Left rear lamp

Backup buzzer

Backup switch

Figure 10-28 Schematic diagram for backup warning system

1. Principle description: When the electric lock is turned on, the 10A backup warning fuse is turned on (24V). When shifted to reverse gear, the backup switch is turned on, the wire 9# is turned on, and the backup warning buzzer sounds. At the same time, the backup lamps on the left and right rear lamps light up. 61


2. Analysis of Common Malfunctions The backup warning buzzer fails to sound when the electric lock is turned on and the reverse gear is engaged. 1. Check the 10A backup warning buzzer fuse for burnout. 2. Check the connectors and wires for secure and reliable connections. Generally, the loose connector or worn harness will lead to middle open-circuit of wire 9#. 3. Check the backup switch for damage. If normal, two wires of the backup switch are connected when the reverse gear is engaged. 4. If no problem is detected in above checking items, check the voltage of wire 9# at the backup warning buzzer. If the voltage is normal (24V), it indicates that the backup warning buzzer is damaged and shall be replaced. If no voltage is detected, generally the connector is loose or the harness is worn. Analysis of common malfunctions: After the electric lock is turned on, the backup warning buzzer sounds constantly no matter which gear is engaged. This problem is generally caused by the bonded contact of backup switch. In few cases, it’s caused by the short-circuit between wire 9# and certain power wire.

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Section VII Wiper and Washer System

1. Principle description 1.1 Principle of washer: When the electric lock is turned on, the 10A wiper fuse is powered on (24V) to turn on the washer switch (it’s an automatic resetting rocker switch. Please refer to the Accessories – Rocker Switch for details) so that the washer motor (installed on the water reservoir) is powered on via wire 37# to pump the water from water reservoir to the nozzles (installed beneath the front windscreen of the cab) and spray onto the windscreen. Rocker switch of washer reservoir (with resetting function) Terminal

Spray motor

Rocker switch of front wiper Terminal

Position

Position

OFF

OFF

Front wiper

Figure 10-29 Schematic diagram of wiper and washer system

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1.2 Principle of wiper: The wiper motor is a permanent magnet motor that adopts the positive control mode. As shown in the figure, the wiper motor has 4 output wires, of which the red is the power wire (the public wire for high speed armature and low speed armature), the black wire is the resetting wire, the blue wire is another brush wire for high speed armature, and the white wire is another brush wire for low speed armature. When the electric lock is turned on, the wire 37# is powered on (24V). If the wiper switch (refer to Accessories – Rocker Switch for details) is at position I, the pin 37# and pin 24# are connected and the motor runs under low speed mode. If the wiper switch is at position II, the pin 37# and pin 26# are connected and the motor runs under high speed mode. If the wiper switch is turned off (namely rotate from position I to position “OFF”), the pin 24# and pin 25# are connected. At the wiper is not stopped at the initial position at the moment when the switch is turned off, the current flows through wire 25# - wiper switch pin 24# - low speed armature – grounding (Note: There is an internal automatic stop device to ensure that the wiper always stops at initial position. When the wiper is at initial position, the resetting wire is connected to the ground).

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2. Troubleshooting of common malfunctions 2.1 Working failure of wiper motor 1.

Check 10A wiper fuse for burnout.

3.

Check connectors for looseness and harnesses for wear.

2. 4.

Check wiper switch for damage.

Check wiper motor armature for short-circuit or opencircuit.

2.2 No water spray from nozzles 1.

Observe the motor for running and pumping of water.

3.

Check the nozzles for blockage.

2.

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Check water line for interruption (The water pipe is disconnected or over-tightly bundled).


Section VIII Electric horn system Horn assembly

Horn button

Figure 10-30: Schematic diagram for circuit of electric horn

Figure 10-31: Installation location of electric horn

1. Principle description: When the electric lock is turned on, the 10A electric horn fuse is turned on (24V). When the electric horn switch is pressed, the current flows through 10A electric horn fuse – electric horn – electric horn switch – grounding and the electric horn sounds continually (as shown in Figure 8-2).

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2. Troubleshooting of common malfunctions

The electric horn fails to sound when the electric lock is turned on and the electric horn switch is pressed: 2.1

Check 10A electric horn fuse for burnout.

2.3.

Check connectors for looseness and harnesses for wear.

2.2

2.4

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Check electric horn switch (the button switch in the center of steering gear) for normal functioning. Normally, the wire 12# is grounded when the electric horn button switch is pressed. Check the electric horn for damage (For two wiring posts of the electric horn, connect one post to 24V power supply and connect another to ground. If the electric horn fails to sound, it can be determined as the damage of electric horn).


Section IX Spare Socket System Spare socket

Figure 10-32: Schematic diagram for circuit of spare socket

1. Principle description

Figure 10-33: Installation position of spare socket

When the electric lock is turned on, the 10A spare socket fuse is turned on (24V) to turn on the spare socket through wire 77# and wire 0#. When the external power supply is required, after the external wire and plug are correctly connected, insert into the socket to obtain the power. Please be noted that the consuming power shall not exceed 150W. The spare socket provides a standard DC 24V power socket for connection of external loads such as electric kettle and interphone. The installation position is shown in Figure 10-33.

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2. Troubleshooting of common malfunctions Working failure of spare socket:

2.1 Check the 10A spare socket fuse for burnout.

2.2. Check connectors for looseness and harnesses for wear. 2.3 Check the spare socket for damage.

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THE END

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07 Electric Sysetem LG958L

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