966 f Loader

Copyright 1991, 2012 Caterpillar Inc. All Rights Reserved.

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4YG 966F WHEEL LOADER Systems Operation Media Number SENR5922-02 Publication Date 1994/10/03 Update Date 2001/06/19

Components Description The same transmission control is used on a variety of models. All of the following electrical components are not present on every machine. The control recognizes the machine on which it is installed and knows which components are present. For the location of components see the Electrical System Schematic in the machine Service Manual. Electronic Transmission Control


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NOTE: The preceding chart has been revised.

Electronic circuits within the control make shifting decisions and control the transmission solenoid valves. The control inputs and outputs are connected to the machine harness wiring through a 40 contact connector. Input/Output

The CAT data link is bidirectional, allowing the control to receive and send information. The purpose of the data link is to communicate with the Computerized Monitoring System (CMS). The data link is not a visible component. It consists of internal control circuits and the connecting harness wiring. The transmission control receives harness code information from CMS. The transmission control sends engine speed, transmission speed, transmission gear, transmission direction and transmission


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control faults to CMS to be shown on the CMS display. All electronic controls that use the data link have a module identifier (MID). The MID for this transmission control is the number 81. Inputs

Several types of inputs provide information to the control. Operational

The operational inputs provide information about operator requests to the control. These inputs receive information from the shift handle, downshift, ride control and auto/manual switches. These switches provide an open (floating), ground or battery signal, to the inputs of the control. Option

The option inputs (connector contacts 25, 27 and 30) tell the control what options the machine is equipped with. These inputs are either open or grounded by the options code plug. For the option code of the machine being serviced, see the Option Code chart on the Electrical System Schematic in the machine Service Manual. Service

The service inputs (connector contacts 28 and 29) control the mode of operation and certain diagnostic functions. Grounding service input (connector contact 28) and clear input (connector contact 29) at the same time, initiates changing the control display mode. Removing ground from these two inputs locks the control in the selected mode. Other diagnostic functions are also performed when the service inputs are grounded and/or opened at the proper time. For more information, see the topic Display Modes in the Systems Operation section. Sensor

At each sensor input, an AC signal is present which represents the transmission speed (connector contact 5) and engine speed (connector contact 6). The control measures the frequency (Hz) of the AC signals to determine the transmission and engine speed. The control uses this speed information to make shifting decisions. Outputs Display


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Electronic Transmission Control Display Area (1) Power indicator (green). (2) Readout (component identifier and failure mode identifier). (3) Service mode indicator (yellow). (4) Fault present indicator (red). The display shows the operating status of the electronic transmission control system and diagnostic information. Solenoid

The control sends a voltage to the solenoid outputs to energize solenoids that control various machine functions. These functions are transmission gear selection, ride control activation, engine horsepower selection and air inlet heater activation (using a relay). Switches

Switches provide information (input) to the control. Switches are two state devices. The two states are:

· Closed - the switch closes a circuit to the control input. · Open - the switch opens a circuit to the control input. Park Brake Switch (If Equipped)


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Park Brake Switch (1) Schematic symbol. (2) Switch. The purpose of park brake switch (2) is to tell the control when the park brake is engaged. The control also sends this information to the Computerized Monitoring System (CMS). Park brake switch (2) has two input connections to the control; park brake N/C at connector contact 4 and downshift N/O at connector contact 3. When the park brake is engaged, the park brake N/C circuit is open and the park brake N/O circuit is closed to ground. When the switch is not activated, the park brake N/C circuit is closed to ground and the park brake N/O circuit is open. NOTE: A two pole switch is used for diagnostic purposes. If the two poles are ever in the same state (open or grounded), the control knows a circuit failure is present. Downshift Switch


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Downshift Switch (1) Switch. (2) Schematic symbol. The purpose of downshift switch (1) is to tell the control that the operator wants the transmission to downshift one gear. Downshift switch (1) has two input connections to the control; downshift N/C at connector contact 23 and downshift N/O at connector contact 22. When the operator presses downshift switch (1), the downshift N/C circuit is open and the downshift N/O circuit is closed to ground. When the switch is not activated, the downshift N/C circuit is closed to ground and the downshift N/O circuit is open. NOTE: A two pole switch is used for diagnostic purposes. If the two poles are ever in the same state (open or grounded), the control knows a circuit failure is present. This fault is then shown on the diagnostic indicator; see Diagnostic Indicator Operation. Auto/Manual Switch

Auto/Manual Switch (1) Switch. (2) Schematic symbol. The purpose of auto/manual switch (1) is to tell the control which shift mode the operator wants the control to operate in. Auto/manual switch (1) has two input connections to the control; auto/manual N/C at connector contact 20 and auto/manual N/O at connector contact 21. When the operator selects AUTO mode, the auto/manual N/O circuit is open and the auto/manual N/C circuit is closed to ground. When MANUAL mode is selected, the auto/manual N/O circuit is closed to ground and the auto/manual N/C circuit is open. Air Inlet Heater Switch (If Equipped)


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Air Inlet Heater Switch (1) Switch. (2) Schematic symbol. The purpose of air inlet heater switch (1) is to tell the control that the operator wants to continue to heat the inlet air. Air inlet heater switch (1) has one input connection to the control at connector contact 7. When the operator holds the switch in the heat position, the input to the control is closed to ground. With the switch in the OFF position, the input to the control is open. Ride Control Switch (If Equipped)

Ride Switch (1) Switch. (2) Schematic symbol.


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Machines With Air Over Hydraulic Brakes

The purpose of ride control switch (1) is to tell the control which ride mode (AUTO/ON/OFF) the operator wants the control to operate in. Ride control switch (1) has three input connections to the c ontrol; input 1 at connector contact 10, input 2 at connector contact 11 and input 3 at connector contact 26. When the operator selects AUTO mode, input 2 is open, input 1 is closed to +battery and input 3 is closed to ground. When ON mode is selected, input 2 is closed to +battery, input 1 is open and input 3 is open. When OFF is selected, input 2 is open, input 1 is closed to +battery and input 3 is closed to ground.

Machines With Hydraulic Over Hydraulic Brakes

The purpose of ride control switch (1) is to tell the control which ride mode (AUTO/ON/OFF) the operator wants the control to operate in. Ride control switch (1) has two input connections to the control; input 2 at connector contact 24 and input 3 at connector contact 26. When the operator selects AUTO mode, input 2 is closed to ground and input 3 is open. When ON mode is selected, input 2 is open and input 3 is closed to ground. When OFF is selected, input 2 and input 3 are closed to ground.

Shift Handle Switches


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Shift Handle (1) Handle. (2) Schematic symbol. The shift handle switches are inputs to the control and connect to contacts 12 through 19. The purpose of the switches is to tell the control what gear and direction the operator has selected with the shift handle. The shift handle switches close gear and direction inputs on the control to ground and +battery. The gear and direction selected are the only closed switches; the other direction and gear switches are open. Neutralizer Switch


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Neutralizer Switch (1) Switch. (2) Schematic symbol. During normal operation, neutralizer switch (1) closes the neutralizer input of the shift handle (9 contact connector - contact 1) to battery voltage. Depressing the brake pedal increases the brake oil pressure and opens the neutralizer input line. With this line open, the shift handle cannot close either direction solenoid input of the control (connector contacts 18 and 19) to battery voltage. Without battery voltage at one of these inputs the control neutralizes the transmission. With the transmission neutralized, the direction solenoids are not activated. Neutralizer Override Switch

Neutralizer Override Switch


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(1) Switch. (2) Schematic symbol. When activated, neutralizer override switch (1) closes the neutralizer input of the shift handle (9 contact connector - contact 1) to battery voltage whether the brakes are applied or not. This switch is used to disable the neutralizer switch when neutralizing the transmission during braking is not desired. Sensors

Sensor (Typical Example) (1) Sensor. (2) Schematic symbol. The engine and transmission speed sensors are located on the flywheel housing and the transmission housing respectively. As gear teeth pass the end of each sensor, an AC voltage is produced. The frequency of the voltage is proportional to the speed of the passing gear teeth. The control uses these signals to make shifting decisions. Solenoids


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Transmission Solenoids (1) Solenoid. (2) Schematic symbol. The purpose of the transmission solenoids is to turn on and off the oil flow to the clutches in the transmission. When a direction and gear are selected by the operator or the control, the control activates the appropriate solenoids. For movement of the machine two solenoids are activated; one for direction and one for gear. When activated, a solenoid receives voltage from the control. When in neutral, the 4th gear solenoid is activated. The purpose of the ride control solenoid is to turn on and off the hydraulic oil flow to and from the load dampening system. The dual horsepower/engine shutdown solenoid is one solenoid with two coils, one for each function. The purpose of the dual horsepower portion is to limit the engine rack movement. When high horsepower is activated the control energizes the dual horsepower coil of the solenoid. This allows the engine rack to open more and allows greater fuel flow, increasing the engine horsepower. The solenoids have a connector with two contacts. One contact receives power from the corresponding connector contact (31 through 38) of the control. The other contact of all the solenoids join together and return to connector contact 39 of the control. Air Inlet Heater Relay


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Air Inlet Heater Relay (1) Schematic symbol. (2) Relay. The purpose of the air inlet heater relay is to turn on and off the current flow to the air inlet heater. When the control determines that the air inlet heater should be engaged, the control activates the air inlet heater relay output (connector contact 7), which energizes the air inlet heater relay. The relay has a connector with two contacts. One contact receives power from the control (connector contact 7). The other contact returns to connector contact 39 of the control.


966 f Loader

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