950G Series II Wheel Loader, 962G Series II Wheel Loader and IT62G Series II Integrated Toolcarrier Power Train Caterpillar

Power Train Electronic Control System

Usage:

The main functions of the power train electronic control system follow: "Neutral Start Function", "Manual Shift Function", "Automatic Shift Function", "Transmission Neutralizer Function", "Parking Brake Function", "Backup Alarm Function", "Ride Control Function (If Equipped)" and "Diagnostic Operation".

Neutral Start Function

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Illustration 1	g00329538
Start Relay

The start relay is an output of the power train electronic control module (ECM). The start relay turns the start solenoid on and off. The start solenoid controls the starting motor. When the operator turns the key start switch to the START position and the power train ECM decides that all the starting conditions are satisfied, the power train ECM energizes the start relay with a +battery signal. The power train ECM will not allow the engine to be started unless the transmission direction and speed control lever (if equipped) is in the NEUTRAL position. The power train ECM will not allow the engine to be started unless the transmission direction and speed control lever (if equipped) is in the NEUTRAL position. If the transmission direction and speed control lever (if equipped) or the transmission direction control switch (if equipped) is in the NEUTRAL position, the power train ECM activates the start relay. The start relay allows the starting motor to turn. The power train ECM will not allow the starter to activate if the engine is running.

The start relay has a connector with two contacts. One contact receives power from connector contact J1-8 of the power train ECM. The other contact returns power to connector contact J2-3 of the power train ECM.

Terminal 3 of the start relay connects to a +battery source. Terminal 4 connects to the start solenoid.

Reference: For more information on the key start switch, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Reference: For more information on the power train electronic control module (ECM), refer to the Service Manual module Systems Operation, "Electronic Control Module (Power Train)" for the machine that is being serviced.

Manual Shift Function

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Table 1
Modulating Valve (Transmission Clutch)
Fourth Speed Forward	3 and 2
Third Speed Forward	4 and 2
Second Speed Forward	5 and 2
First Speed Forward	6 and 2
Neutral	3
First Speed Reverse	6 and 1
Second Speed Reverse	5 and 1
Third Speed Reverse	4 and 1
Fourth Speed Reverse	3 and 1

Conventional Steering

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Illustration 2	g00823325
(1) Autoshift control switch. (2) Manual position.

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Illustration 3	g00823334
(3) Transmission downshift switch.

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Illustration 4	g00823383
(4) Transmission direction and speed control lever.

In order to manually shift the transmission, the autoshift control switch (1) must be in the MANUAL position (2). Shifting the transmission is the main function of the power train electronic control module (ECM). The power train ECM interprets the changes in the switch position. After the power train ECM interprets the changes in the switch position, the power train ECM shifts the transmission.

Transmission direction and speed control lever (4) is a sealed unit. The transmission direction and speed control lever is mounted on the steering column. The transmission direction and speed control lever allows the operator to select a speed range by rotating the control lever. The operator can select a direction by moving the transmission direction and speed control lever forward or backward. The transmission will remain in the selected direction until the transmission direction and speed control lever is moved forward or backward. The transmission will remain in the selected speed until the transmission direction and speed control lever is rotated to a different speed.

When transmission downshift switch (3) is depressed, the transmission downshift switch signals the power train ECM to downshift the transmission by one speed. Pressing and holding the transmission downshift switch signals the power train ECM to continue to downshift the transmission.

If second speed forward or second speed reverse are selected, the transmission will shift to first speed by depressing transmission downshift switch (3). The transmission will remain in first speed until transmission direction and speed control lever (4) is shifted into the opposite direction or to the NEUTRAL position.

When the key start switch is turned from the OFF position to ON position, the power train ECM is activated. When the power train ECM is first activated all of the clutch solenoid modulating valves are de-energized. The clutch solenoid modulating valves are de-energized regardless of the position of transmission direction and speed control lever (4). The power train ECM then determines if the transmission direction and speed control lever is in the NEUTRAL position. The power train ECM disables the transmission if the NEUTRAL position is NOT selected. If the NEUTRAL position is NOT selected, the transmission direction and speed control lever must be returned to the NEUTRAL position before a direction can be selected. The power train ECM activates the start relay and the power train ECM allows the engine to start if the transmission direction and speed control lever is in the NEUTRAL position. The power train ECM allows the initial selected speed to be changed if the transmission direction and speed control lever is in the NEUTRAL position.

Note: Transmission direction and speed control lever (4) must be in the NEUTRAL position when the key start switch is turned to the START position. If the transmission direction and speed control lever is not in the NEUTRAL position, the start relay will not be activated when the key start switch is turned. For additional information on the neutral start function, refer to "Neutral Start Function".

Reference: For more information on the switches for the transmission direction and speed control lever, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Reference: For more information on the key start switch, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Command Control Steering

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Table 2
Normal Shifting Sequence
Speed Range and Direction	REVERSE Position Transmission Shift	NEUTRAL Position Transmission Shift	FORWARD Position Transmission Shift	UP SHIFT Position Transmission Shift	DOWN SHIFT Position Transmission Shift
4F	4R	Neutral ⁽¹⁾ (4N)	No Change	No Change	3F
3F	3R	Neutral ⁽¹⁾ (3N)	No Change	4F	2F
2F	2R	Neutral ⁽¹⁾ (2N)	No Change	3F	1F
1F	1R	Neutral ⁽¹⁾ (1N)	No Change	2F	No Change
Neutral ⁽¹⁾ (1N, 2N, 3N, 4N)	Last ⁽²⁾	No Change	Last ⁽²⁾	Next ⁽³⁾	Prior ⁽³⁾
1R	No Change	Neutral ⁽¹⁾ (1N)	1F	2R	No Change
2R	No Change	Neutral ⁽¹⁾ (2N)	2F	3R	1R
3R	No Change	Neutral ⁽¹⁾ (3N)	3F	4R	2R
4R	No Change	Neutral ⁽¹⁾ (4N)	4F	No Change	3R

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^( 1 )	The speed and the direction that is shown in bold print is the gear readout.
^( 2 )	A directional shift out of neutral will cause a speed shift to the last speed that was selected in either forward or reverse.
^( 3 )	Speed shifts are allowed when neutral is selected. The gear readout will change the speed that is shown when neutral is selected and a speed shift is made. However, none of the solenoids are activated until forward or reverse is selected.

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Illustration 5	g00823503
(5) Autoshift control switch. (6) Manual position.

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Illustration 6	g00823455
(7) Transmission direction control switch. (8) Transmission speed selector switch.

The autoshift control switch (5) tells the power train ECM of the desired shift mode, AUTO mode or MANUAL mode. In order to manually shift the transmission, the autoshift control switch must be in the MANUAL position (6). Shifting the transmission is the main function of the power train electronic control module (ECM). The power train ECM interprets the changes in the switch position. After the power train ECM interprets the changes in the switch position, the power train ECM shifts the transmission.

The transmission direction control switch (7) and the transmission speed selector switch (8) are located on the steering wheel. The transmission direction control switch is a three-position switch that selects either forward, neutral, or reverse.

The operator selects a direction by moving transmission direction control switch (7) to one of three positions. The transmission direction control switch tells the power train ECM of the desired direction of travel.

The transmission speed selector switch (8) is a momentary rocker switch. The transmission speed selector switch allows the operator to select the speed range of the transmission. Press the top of the transmission speed selector switch in order to increase the speed of the transmission. The power train ECM will upshift the transmission to the next higher gear. Press the bottom of the transmission speed selector switch in order to decrease the speed of the transmission. The power train ECM will downshift the transmission to the next lower gear. Transmission speed selector switch has four input connections at the power train ECM on connector J1.

Note: The correct status of the four input connections is required. This will allow the power train ECM to decide when the power train ECM should make each shift.

Note: The normally closed (N/C) circuit and normally open (N/O) circuit of the transmission downshift switch are used for diagnostic purposes. The normally closed (N/C) circuit and normally open (N/O) circuit of the transmission speed selector switch are used for diagnostic purposes. If the normally closed (N/C) circuit and normally open (N/O) circuit are open at the same time, the power train ECM records a fault. If the normally closed (N/C) circuit and normally open (N/O) circuit are grounded at the same time, the power train ECM records a fault.

When the key start switch is turned from the OFF position to ON position, the power train ECM is activated. When the power train ECM is first activated all of the clutch solenoid modulating valves are de-energized. The clutch solenoid modulating valves are de-energized regardless of the position of transmission direction control switch (5). The power train ECM then determines if transmission direction control switch (7) is in the NEUTRAL position. The power train ECM disables the transmission if the NEUTRAL position is NOT selected. If the transmission direction control switch is in the NEUTRAL position, the power train ECM selects the current speed and the current direction as neutral. The power train ECM activates the start relay if the transmission direction control switch is in the NEUTRAL position. When the start relay is activated, the engine is allowed to start.

Note: Transmission direction control switch (7) must be in the NEUTRAL position when the key is turned to the START position. If the transmission direction control switch is not in the NEUTRAL position, the start relay will not be activated. For additional information on the neutral start function, refer to "Neutral Start Function".

Reference: For more information on the Caterpillar Monitoring System, refer to the Service Manual module Systems Operation, "Monitoring System (Power Train Functions)" for the machine that is being serviced.

Reference: For additional information on the transmission direction control switch and the transmission speed selector switch, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Reference: For more information on the key start switch, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Automatic Shift Function

Conventional Steering

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Illustration 7	g00823628
(1) Autoshift control switch. (2) "2-4" position. (3) "1-4" position.

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Illustration 8	g00823640
(4) Downshift switch.

The transmission can be shifted automatically. There are two modes of automatic operation: (2) 1-4 position. and (3) 2-4 position.

The automatic mode of operation is represented by two numbers that are separated by a dash. The first number indicates the speed of the transmission when the transmission is placed into reverse. The second number indicates the highest speed of the transmission when the machine is travelling forward.

For example, place the autoshift control switch into the 2-4 position. The machine will automatically shift into second gear when the transmission is placed into reverse. The transmission will automatically upshift into fourth gear when the transmission is placed into forward.

Use the transmission downshift switch (4) that is located on the lift lever on the right side of the operator's compartment in order to downshift the transmission. This switch is normally used to downshift from second speed to first speed in order to load a bucket. The transmission will remain in the downshifted gear for three seconds after the switch is released. Then, automatic shifting will resume.

Note: If a downshift would cause an engine overspeed condition, the power train ECM will prevent the downshift from occurring.

Command Control Steering

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Illustration 9	g00823631
(5) Autoshift control switch. (6) 2-4 position. (7) 2-3 position. (8) 2 position. (9) 1-4 position.

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Illustration 10	g00823646
(10) Transmission direction control switch. (11) Transmission speed selector switch.

The autoshift control switch is used to select the top speed for the transmission when the transmission is in the AUTO mode.

The transmission can be shifted automatically. There are four modes of automatic operation: (6) 2-4 position., (7) 2-3 position., (8) 2 position. and (9) 1-4 position.

The automatic mode of operation is represented by two numbers that are separated by a dash. The first number indicates the top speed of the transmission when the transmission is placed into reverse. The second number indicates the highest speed of the transmission when the machine is travelling forward.

For example, place the autoshift control switch into the 2-3 position. The machine will automatically shift into second gear when the transmission is placed into reverse. The transmission will automatically upshift into third speed when the transmission is placed into forward.

When the machine is operating in "AUTO" mode, the transmission speed selector switch (11) can be used in order to downshift the transmission. This switch is normally used to downshift from second speed to first speed in order to load a bucket. The transmission will remain in the downshifted gear for three seconds after the switch is released. Then, automatic shifting will resume.

Note: If a downshift would cause an engine overspeed condition, the power train ECM will prevent the downshift from occurring.

Transmission Neutralizer Function

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Illustration 11	g00823991
(1) Left pedal position sensor.

Left pedal position sensor (1) is located in the cab in the left brake pedal assembly. The left pedal position sensor is a pulse width modulated (PWM) sensor. The left pedal position sensor informs the power train ECM of the position of the left brake pedal. When the left brake pedal is depressed, the left pedal position sensor sends a PWM signal to the power train ECM. The power train ECM uses the PWM input in order to neutralize the transmission.

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Illustration 12	g00739087
Transmission neutralizer override switch

The transmission neutralizer override switch is an input of the power train ECM. The input is used by the power train ECM to decide if the transmission neutralizer should be disabled. The transmission neutralizer override switch is a momentary rocker switch.

Left pedal position sensor (1) signals the power train ECM to neutralize the transmission if the transmission neutralizer is enabled. When the machine is started, the transmission neutralizer is enabled. When the transmission neutralizer override switch is depressed and released, the transmission neutralizer is alternately enabled or disabled.

The transmission is neutralized by de-energizing the selected direction clutch solenoid. The selected speed clutch solenoid is still energized. The engine rpm will increase when the transmission is neutralized due to the no-load condition from the transmission. This allows full hydraulic power for bucket operation.

Note: When the transmission is neutralized, the readout on the Caterpillar Monitoring System continues to show the speed that is selected but the direction will read neutral.

Reference: For more information on the left pedal position sensor, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Reference: For more information on the transmission neutralizer override switch, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Parking Brake Function

The parking brake function prevents the operator from operating the machine while the parking brake is engaged. Driving through the parking brake causes accelerated wear to the friction components of the parking brake.

When the parking brake control is disengaged, the transmission will shift normally. When the parking brake control is engaged, the transmission will not shift out of neutral to first speed forward or first speed reverse. If the transmission is in first speed forward or in first speed reverse and the parking brake is moved to the engaged position, the transmission will shift into neutral. All of the modulating valves (transmission clutch) are de-energized. If the transmission is in second speed forward or in third speed forward, the transmission will remain engaged.

The parking brake function activates a warning category 1 or a warning category 3 on the Caterpillar Monitoring System.

Warning category 1 is activated whenever the parking brake is engaged. The parking brake indicator will flash.

While the parking brake is engaged, warning category 3 will be activated. This will occur if the operator places the transmission direction control lever (if equipped) or the transmission direction control switch (if equipped) in the FORWARD position or the REVERSE position. The parking brake indicator will flash and the action light will flash. The action alarm will sound.

When the parking brake is engaged and the transmission is in first speed, the power train ECM shifts the transmission to neutral. The power train ECM also sends the parking brake status to the Caterpillar Monitoring System via the CAT Data Link. When the parking brake is engaged, the alert indicator for the parking brake flashes on the Caterpillar Monitoring System. If the operator selects the FORWARD position or the REVERSE position and the parking brake is engaged, the Caterpillar Monitoring System initiates a Warning Category 3. A Warning Category 3 causes the parking brake indicator and the action lamp to flash. The action alarm will also sound.

Reference: For more information on the Caterpillar Monitoring System, refer to the Service Manual module Systems Operation, "Monitoring Systems (Power Train Functions)" for the machine that is being serviced.

Reference: For more information on the parking brake pressure switch, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

Driving Through the Parking Brake

The power train ECM will allow the operator to drive through the parking brake. The machine should be moved only for a short distance.

In order to drive through the parking brake, the operator must select first speed forward or first speed reverse. The operator must then move the transmission direction control lever (if equipped) or the transmission direction control switch (if equipped) to the NEUTRAL position. The operator must then move the transmission direction control lever (if equipped) or the transmission direction control switch (if equipped) to the previous direction that was selected.

Backup Alarm Function

The backup alarm function alerts surrounding personnel that the machine is backing up. The backup alarm is an output of the power train electronic control module (ECM). The power train ECM activates the backup alarm relay when the transmission direction control lever (if equipped) or the transmission direction control switch (if equipped) is in the REVERSE position. The backup alarm relay then activates the backup alarm. The backup alarm receives a +battery signal from the power train ECM when the backup alarm is activated.

The backup alarm has two terminals for electrical connections. One terminal receives power from connector contact J2-37 of the power train ECM. The other contact returns power to connector contact J2-3 and J1-7 of the power train ECM.

Ride Control Function (If Equipped)

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Illustration 13	g00824031
(1) Ride control switch.

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Illustration 14	g00824038
Indicator display (2) Ride control ON. (3) Ride control AUTO.

Ride control is an optional function that is enabled by a programmable parameter via the Caterpillar Electronic Technician (ET). Ride control can also be enabled by the calibration mode of the Caterpillar Monitoring System. Ride control is enabled when the operator places the ride control switch (1) in the ON position or the AUTO position. In the ON position, ride control is activated at all times and the power train ECM continuously energizes the ride control solenoid. In the AUTO position, ride control is activated when the machine ground speed increases above approximately 6 mph. In the AUTO position, ride control is deactivated when the machine ground speed is below approximately 5.5 mph. The default speed can be changed with the configuration screen of the Caterpillar Electronic Technician (ET). As ride control is activated and deactivated the ride control solenoid is energized and de-energized.

The two ride control solenoids for the ride control are outputs of the power train ECM. The ride control solenoids turn the ride control system on and off. When ride control is disabled, the number one ride control solenoid is de-energized and the number two ride control solenoid is energized. When ride control is enabled, the number one ride control solenoid is energized 5 seconds after the number two ride control solenoid is de-energized. The delay time can be changed with the ride control equalization pressure time parameter of the Caterpillar Electronic Technician (ET). Both of the ride control solenoids have a connector with two contacts. The number one ride control solenoid receives power from the connector contact J1-18 of the power train ECM. The number two ride control solenoid receives power from the connector contact J1-12 of the power train ECM. Both of the ride control solenoids return power to connector contact J2-3 of the power train ECM.

Diagnostic Operation

The power train electronic control module (ECM) detects faults that occur in most of the input circuits and the output circuits. A fault is detected when the signal at the contact of the power train ECM is outside a valid range. The power train ECM then records the fault. If the fault goes away, the fault information remains stored for future reference.

The diagnostics of the power train ECM are available to assist with the troubleshooting of detected faults. A service code is used to specify each fault. These service codes are shown in the display area of the Caterpillar Monitoring System. Service codes consist of three identifiers: MID, CID and FMI.

Module Identifier (MID) - The MID is a three-digit code that is shown on the display area. The MID is shown for approximately one second before the service code that is shown in the same area. The power train ECM that has diagnosed the fault is logged by the MID. The following examples are of some MID.

Caterpillar Monitoring System ... 030

Power Train ECM ... 081

Note: The MID of the power train control is "081". Before troubleshooting the power train, make sure that "081" is the service code of the fault. The Caterpillar Monitoring System also shows service codes of the faults that are not related to the power train system. MID 081 identifies the power train ECM as the source of the service code.

Component Identifier (CID) - The components that are faulty are noted by the CID. The following components are examples: start relay and reverse solenoid. The CID is a four digit code that is shown on the display area. The CID and the FMI are shown together after the MID has been displayed.

Reference: For a list of the CID codes for the power train ECM, refer to the Service Manual module Testing And Adjusting, "Troubleshooting Diagnostic Codes" for the machine that is being serviced.

Failure Mode Identifier (FMI) - The FMI tells the type of failure that has occurred. The following situations are examples: voltage above normal, current below normal and abnormal frequency. The FMI is a two digit code that is shown on the display area. The CID and the FMI are shown together after the MID has been displayed. A decimal point "." precedes the FMI.

Reference: For a list of the FMI codes for the power train ECM, refer to the Service Manual module Testing And Adjusting, "Troubleshooting Diagnostic Codes" for the machine that is being serviced.

The power train ECM does not have a display area for displaying diagnostic information to service personnel. Diagnostic information concerning the power train system is sent on the CAT Data Link to the Caterpillar Monitoring System. Service personnel must be familiar with the Caterpillar Monitoring System in order to troubleshoot the power train system.

The service mode of the Caterpillar Monitoring System allows service personnel to see the faults that were detected by the power train ECM. The service mode of the Caterpillar Monitoring System allows service personnel to troubleshoot the faults that were detected by the power train ECM. While the Caterpillar Monitoring System is in the service mode, the service code for any detected fault of the power train electronic control system is shown in the display area of the Caterpillar Monitoring System.

When the service mode is first entered, all service codes for any detected faults scroll in the display area. For troubleshooting and clearing, the particular service code must be placed on hold. The display area continuously alternates between showing the MID, and then showing both the CID and the FMI of the particular service code for the fault that is on hold.

The Caterpillar Monitoring System enters service mode when ground is removed from the service input and the clear input. The mode number 3 for service mode is shown in the display area of the Caterpillar Monitoring System. To place a service code for a fault on hold, ground the service input. To clear a service code for a fault on hold, ground the clear input. The Caterpillar Monitoring System exits service mode when ground is added to the service input and the clear input.

Note: The time that is needed to clear a fault and the time that is needed to set a fault can last less than 1 second up to 60 seconds.

Reference: For more information on the CAT Data Link, refer to the Service Manual module Systems Operation, "CAT Data Link" for the machine that is being serviced.

Note: The Service Manual modules Systems Operation, Testing and Adjusting, "Caterpillar Monitoring System" should only be used as a reference to the display of the faults of the power train electronic control system.