966H, 972H and 980H Wheel Loaders Power Train Electronic Control System Caterpillar

Illustration 1	g00908031
Schematic for the Transmission Hydraulic System (1) Transmission hydraulic control relief valve (2) Torque converter (3) Torque converter outlet relief valve (if equipped) (4) Transmission oil filter (5) Modulating valve (transmission clutch) for the Number 1 clutch (6) Modulating valve (transmission clutch) for the Number 4 clutch (7) Modulating valve (transmission clutch) for the Number 2 clutch (8) Modulating valve (transmission clutch) for the Number 5 clutch (9) Modulating valve (transmission clutch) for the Number 3 clutch (10) Modulating valve (transmission clutch) for the Number 6 clutch (11) Transmission oil pump (12) Torque converter inlet relief valve (13) Suction screen and magnet (14) Oil sump (15) Transmission lubrication (16) Oil cooler (A) Pump pressure tap at the transmission hydraulic control relief valve (B) P3 Torque converter inlet pressure tap (C) Torque converter outlet pressure tap (D) Sampling valve for the transmission oil (G) Pressure tap for the Number 1 clutch (H) Pressure tap for the Number 4 clutch (J) Pressure tap for the Number 2 clutch (K) Pressure tap for the Number 5 clutch (L) Pressure tap for the Number 3 clutch (M) Pressure tap for the Number 6 clutch (N) Transmission lubrication pressure tap

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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine.

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Escaping fluid under pressure, even a pinhole size leak, can penetrate body tissue, causing serious injury, and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak.

Operational Checks

Operate the machine in each direction and in all speeds. Note the noises that are not normal and find the sources of the noises. If the machine is not operating correctly, refer to the "Troubleshooting Problem List" below.

Make sure that you check for any service codes that have been generated before troubleshooting a problem.

ReferenceFor more information on checking for service codes with the Caterpillar Monitoring System, refer to Testing and Adjusting, "Using Caterpillar Monitoring System to Determine Service Codes".

ReferenceFor more information on checking for service codes with the Caterpillar Electronic Technician (ET), refer to Testing and Adjusting, "Using Caterpillar Electronic Technician (ET) to Determine Service Codes".

ReferenceFor additional information about troubleshooting service codes, refer to Testing and Adjusting, "Troubleshooting Service Codes".

Troubleshooting Problem List

• The transmission does not operate in any speed or the transmission slips in all speeds.

• The transmission overheats.

• There is pump noise that is not normal.

• There is noise in the transmission that is not normal.

• The transmission operates in FORWARD only.

• The transmission operates in REVERSE only.

• The transmission does not operate in FIRST SPEED FORWARD or in FIRST SPEED REVERSE.

• The transmission does not operate in SECOND SPEED FORWARD or in SECOND SPEED REVERSE.

• The transmission does not operate in THIRD SPEED FORWARD or in THIRD SPEED REVERSE.

• The transmission does not operate in FOURTH SPEED FORWARD or in FOURTH SPEED REVERSE.

• The transmission does not disengage when the transmission direction and speed control lever (if equipped) is in the NEUTRAL position.

• The transmission does not disengage when the transmission direction control switch (if equipped) is in the NEUTRAL position.

• The transmission will not upshift to the maximum selected gear in the Auto mode or the Manual mode.

• Pressure is low at direction clutch pressure tap (J) when the machine is operated in FORWARD speeds.

• Pressure is low at direction clutch pressure tap (G) when the machine is operated in REVERSE speeds.

• Pressure is low at speed clutch pressure tap (M) when the machine is operated in FIRST speed.

• Pressure is low at speed clutch pressure tap (K) when the machine is operated in SECOND speed.

• Pressure is low at speed clutch pressure tap (H) when the machine is operated in THIRD speed.

• Pressure is low at speed clutch pressure tap (L) when the machine is operated in FOURTH speed.

• Pressure is high at direction clutch pressure tap (J) when the machine is operated in FORWARD speeds.

• Pressure is high at direction clutch pressure tap (G) when the machine is operated in REVERSE speeds.

• Pressure is high at speed clutch pressure tap (M) when the machine is operated in FIRST speed.

• Pressure is high at speed clutch pressure tap (K) when the machine is operated in SECOND speed.

• Pressure is high at speed clutch pressure tap (H) when the machine is operated in THIRD speed.

• Pressure is high at speed clutch pressure tap (L) when the machine is operated in FOURTH speed.

• Clutch engagement is sudden. (This causes jerky shifting.)

• Clutch engagement is slow. (This causes slow shifting in all gears.)

• Clutch engagement is slow in all FORWARD speeds, in all REVERSE speeds, or in any one speed (FORWARD and REVERSE).

• The transmission neutralizer is actuated and the transmission remains engaged.

• The machine does not move and the engine lugs when the transmission is engaged.

• The engine is running and the parking brake is engaged. However, the action alarm does not sound when the transmission is shifted into the FORWARD direction or into the REVERSE direction.

• The backup alarm does not sound when the transmission is shifted into the REVERSE direction.

Troubleshooting

Note: In the following section, when components are referenced with a number, refer to the schematic in Illustration 1.

ReferenceFor additional information about troubleshooting the power train electronic control module (ECM), refer to Testing and Adjusting, "Troubleshooting Service Codes".

Probable Causes of Power Train Problems

Problem: The transmission does not operate in any speed or the transmission slips in all speeds.

Probable causes:

1. The transmission fuse is missing or broken.

2. There is a problem in the electrical circuit for the transmission.

3. The system voltage is low.

4. The transmission direction and speed control (if equipped) is faulty.

5. The transmission direction control switch (if equipped) is faulty.

6. The upshift switch (if equipped) or the downshift switch (if equipped) is faulty.

7. The oil pressure is low. This may be caused by any of the following conditions:

   1. The oil level is low.

   2. There is a restriction in the oil flow circuit or a dirty oil strainer.

   3. The oil pump has failed.

   4. Air leaks on the inlet side of the pump.

   5. There is oil leakage inside the transmission (worn seals around the clutch piston).

   6. The transmission hydraulic control relief valve (1) is not adjusted correctly. The transmission hydraulic control relief valve is stuck open.

8. There is a torque converter failure.

9. There is a mechanical failure in the transmission.

10. Clutch discs and clutch plates are excessively worn.

11. The transmission neutralizer limit switch is not operating.

Problem: The transmission overheats.

Probable causes:

1. The coolant level in the radiator is low.

2. The machine is being used for the wrong application. There is too much torque converter slip, which is caused by too much load.

3. An incorrect transmission gear is being used for the load that is on the machine. Shift to a lower gear.

4. The temperature gauge is faulty.

5. The oil level is too high or too low.

6. The oil cooler or oil lines are restricted.

7. The clutch slips too much. This may be caused by any of the following conditions:

   1. Low oil pressure. Refer to "Problem: The transmission does not operate in any speed or the transmission slips in all speeds."

   2. A clutch is damaged.

8. Oil flow is low. This may be caused by pump wear or by leakage in the hydraulic system.

9. There is air in the oil. This may be caused by air leaks on the intake side of the pump.

10. Torque converter inlet relief valve (12) is stuck open. This causes low oil flow through the torque converter.

11. The clutch or clutches are not fully released. (This is called clutch drag.) This may be caused by any of the following conditions:

    1. Clutch plates or clutch discs are warped.

    2. A return spring is broken or weak.

    3. A modulating valve is stuck at a partial pressure.

Problem: There is pump noise that is not normal.

Probable causes:

1. A loud noise at short intervals indicates foreign material in the transmission hydraulic system.

2. A constant loud noise indicates pump failure.

3. There is air at the inlet side of the pump.

Problem: Noise in the transmission that is not normal

Probable causes:

1. Gears are damaged.

2. The teeth of the clutch plates are worn and/or the teeth of the clutch discs are worn.

3. Clutch plates are slipping and the clutch discs are making noise.

4. Other transmission components may be worn or damaged.

Problem: The transmission operates in FORWARD only.

Probable causes:

1. Number 1 REVERSE modulating valve (5) is inoperative.

2. There is a problem in the electrical circuit.

3. The REVERSE clutch is not engaged or the REVERSE clutch slips. This may be caused by any of the following conditions:

   1. There is low oil pressure due to leaking piston seals.

   2. The clutch discs and clutch plates have too much wear.

   3. Clutch components are broken.

Problem: The transmission operates in REVERSE only.

Probable causes:

1. Number 2 FORWARD modulating valve (7) is inoperative.

2. There is a problem in the electrical circuit.

3. The FORWARD clutch is not engaged or the FORWARD clutch slips. This may be caused by any of the following conditions:

   1. There is low oil pressure due to leaking piston seals.

   2. The clutch discs and clutch plates have too much wear.

   3. Clutch components are broken.

Problem: The transmission does not operate in FIRST SPEED FORWARD position or in FIRST SPEED REVERSE position.

Probable causes:

1. Number 6 FIRST SPEED modulating valve (10) is inoperative.

2. There is a problem in the electrical circuit.

3. The FIRST SPEED clutch is not engaged or the FIRST SPEED clutch slips. This may be caused by any of the following conditions:

   1. There is low oil pressure due to leaking piston seals.

   2. The clutch discs and clutch plates have too much wear.

   3. Clutch components are broken.

Problem: The transmission does not operate in SECOND SPEED FORWARD position or in SECOND SPEED REVERSE position.

1. Number 5 SECOND SPEED modulating valve (8) is inoperative.

2. There is a problem in the electrical circuit.

3. The SECOND SPEED clutch is not engaged or the SECOND SPEED clutch slips. This may be caused by any of the following conditions:

   1. There is low oil pressure due to leaking piston seals.

   2. The clutch discs and clutch plates have too much wear.

   3. Clutch components are broken.

Problem: The transmission does not operate in THIRD SPEED FORWARD position or in THIRD SPEED REVERSE position.

Probable causes:

1. Number 4 THIRD SPEED modulating valve (6) is inoperative.

2. There is a problem in the electrical circuit.

3. The THIRD SPEED clutch is not engaged or the THIRD SPEED clutch slips. This may be caused by any of the following conditions:

   1. There is low oil pressure due to leaking piston seals.

   2. The clutch discs and clutch plates have too much wear.

   3. Clutch components are broken.

Problem: The transmission does not operate in FOURTH SPEED FORWARD position or in FOURTH SPEED REVERSE position.

Probable causes:

1. Number 3 FOURTH SPEED modulating valve (9) is inoperative.

2. There is a problem in the electrical circuit.

3. The FOURTH SPEED clutch is not engaged or the FOURTH SPEED clutch slips. This may be caused by any of the following conditions:

   1. There is low oil pressure due to leaking piston seals.

   2. The clutch discs and clutch plates have too much wear.

   3. Clutch components are broken.

Problem: Transmission clutches do not disengage when the transmission direction and speed control lever (if equipped) is in the NEUTRAL position.

Probable causes:

1. There is a problem in the electrical circuit. When the ECM detects a fault with a solenoid coil the ECM will alert the operator and the ECM will log a fault code.

2. A direction clutch is engaged. Internal components are damaged. The piston for the clutch is wedged in the bore. The discs of the clutch have expanded due to contamination.

Problem: Transmission clutches do not disengage when the transmission direction control switch (if equipped) is in the NEUTRAL position.

Probable causes:

1. There is a problem in the electrical circuit. When the ECM detects a fault with a solenoid coil the ECM will alert the operator and the ECM will log a fault code

2. A direction clutch is engaged. Internal components are damaged. The piston for the clutch is wedged in the bore. The discs of the clutch have expanded due to contamination.

Problem: The transmission will not upshift to the maximum selected gear in the Auto mode or the Manual mode.

Probable causes:

1. There is a problem in the electrical circuit.

2. The left brake pedal is not returning to the fully released position.

Problem: Pressure is low at direction clutch pressure tap (J) when the machine is operated in FORWARD speeds.

Probable causes:

1. There is a problem in the electrical circuit.

2. There is too much leakage in the piston seals of the FORWARD clutch.

3. Number 2 FORWARD modulating valve (7) is not correctly calibrated.

4. Number 2 FORWARD modulating valve (7) is contaminated.

Problem: Pressure is low at direction clutch pressure tap (G) when the machine is operated in REVERSE speeds.

Probable causes:

1. There is a problem in the electrical circuit.

2. There is too much leakage in the piston seals of the REVERSE clutch.

3. Number 1 REVERSE modulating valve (5) is not correctly calibrated.

4. Number 1 REVERSE modulating valve (5) is contaminated.

Problem: Pressure is low at speed clutch pressure tap (M) when the machine is operated in FIRST speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. There is too much leakage in the piston seals of the FIRST SPEED clutch.

3. Number 6 FIRST SPEED modulating valve (10) is not correctly calibrated.

4. Number 6 FIRST SPEED modulating valve (10) is contaminated.

Problem: Pressure is low at speed clutch pressure tap (K) when the machine is operated in SECOND speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. There is too much leakage in the piston seals of the SECOND SPEED clutch.

3. Number 5 SECOND SPEED modulating valve (8) is not correctly calibrated.

4. Number 5 SECOND SPEED modulating valve (8) is contaminated.

Problem: Pressure is low at speed clutch pressure tap (H) when the machine is operated in THIRD speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. There is too much leakage in the piston seals of the THIRD SPEED clutch.

3. Number 4 THIRD SPEED modulating valve (6) is not correctly calibrated.

4. Number 4 THIRD SPEED modulating valve (6) is contaminated.

Problem: Pressure is low at speed clutch pressure tap (L) when the machine is operated in FOURTH speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. There is too much leakage in the piston seals of the FOURTH SPEED clutch.

3. Number 3 FOURTH SPEED modulating valve (9) is not correctly calibrated.

4. Number 3 FOURTH SPEED modulating valve (9) is contaminated.

Problem: Pressure is high at direction clutch pressure tap (J) when the machine is operated in FORWARD speeds.

Probable causes:

1. There is a problem in the electrical circuit.

2. Number 2 FORWARD modulating valve (7) is not correctly calibrated.

Problem: Pressure is high at direction clutch pressure tap (G) when the machine is operated in REVERSE speeds.

Probable causes:

1. There is a problem in the electrical circuit.

2. Number 1 REVERSE modulating valve (5) is not correctly calibrated.

Problem: Pressure is high at speed clutch pressure tap (M) when the machine is operated in FIRST speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. Number 6 FIRST SPEED modulating valve (10) is not correctly calibrated.

Problem: Pressure is high at speed clutch pressure tap (K) when the machine is operated in SECOND speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. Number 5 SECOND SPEED modulating valve (8) is not correctly calibrated.

Problem: Pressure is high at speed clutch pressure tap (H) when the machine is operated in THIRD speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. Number 4 THIRD SPEED modulating valve (6) is not correctly calibrated.

Problem: Pressure is high at speed clutch pressure tap (L) when the machine is operated in FOURTH speed.

Probable causes:

1. There is a problem in the electrical circuit.

2. Number 3 FOURTH SPEED modulating valve (9) is not correctly calibrated.

Problem: Clutch engagement is sudden. (This causes jerky shifting.)

Probable causes:

1. Modulating valves (5), (6), (7), (8), (9), (10) need to be calibrated.

   ReferenceFor additional information about calibrating the modulating valves, refer to Testing and Adjusting, "Calibration and Programming".

   ReferenceFor additional information about calibrating the modulating valves, refer to Testing and Adjusting, "Fill Time for the Transmission Clutch - Calibrate".

2. Modulating valves are unstable.

3. A speed sensor has malfunctioned.

Problem: Clutch engagement is slow. (This causes slow shifting in all gears.)

Probable causes:

1. Oil pressure is low. Refer to "Problem: The transmission does not operate in any speed or the transmission slips in all speeds."

Problem: Clutch engagement is slow in all FORWARD speeds, in all REVERSE speeds, or in any one speed (FORWARD and REVERSE).

Probable causes:

1. The clutch pressure is low because of leaking seals on the piston for the affected speed.

2. The corresponding modulating valve is contaminated.

Problem: The transmission neutralizer is actuated and the transmission remains engaged.

Probable causes:

1. The left pedal position sensor must be calibrated.

2. The left pedal position sensor has failed.

3. The transmission direction and speed control (if equipped) is faulty.

4. The transmission direction control switch (if equipped) is faulty.

Problem: The machine does not move and the engine lugs when the transmission is engaged.

Probable causes:

1. The service brakes are locked up.

2. The parking brake is not released or the parking brake may be locked up.

3. There is a mechanical failure in the front differential or in the rear differential.

4. There is a mechanical failure in a final drive.

5. The gears in the transmission do not turn.

   1. Too many clutches are engaged.

   2. There is a mechanical failure in the transmission.

Problem: The engine is running and the parking brake is engaged. However, the parking brake alarm does not sound when the transmission is shifted into the FORWARD direction or into the REVERSE direction.

Probable causes:

1. The parking brake alarm has failed.

2. There is a problem in the electrical circuit.

Problem: The backup alarm does not sound when the transmission is shifted into REVERSE.

Probable causes:

1. The backup alarm fuse is broken.

2. The backup alarm has failed.

3. There is a problem in the electrical circuit.

4. The transmission direction and speed control (if equipped) is faulty.

5. The transmission direction control switch (if equipped) is faulty.