143H and 163H Motor Graders All Wheel Drive All Wheel Drive System Caterpillar

Performance Checks for the All Wheel Drive System (AWD)

Problem: The AWD piston motors will not engage.

Probable Cause

• There is no power to the AWD ECM.

• The AWD ECM has failed.

• The AWD control has failed.

• One or all of the AWD solenoids have failed.

• The charge solenoid has failed.

• There is no charge pressure or no flow.

Problem: One wheel or both wheels turn in the wrong direction.

Probable Cause

• The hoses may be crossed between the control valve and the motor. Check the hydraulic connections against the hydraulic schematic.

• The hoses may be crossed between the pump and the control valve. Check the hydraulic connections against the hydraulic schematic.

• The solenoid wires may be switched at the pump. Check the electrical connections against the electrical schematic.

Problem: Only one wheel for the AWD system turns when both wheels should turn. The problem exists in the forward and in the reverse direction.

Probable Cause

• Both the forward and the reverse clutch solenoids for that wheel have failed in the CLOSED position. Check the nut that holds the coil on the solenoid. If the nut has been torqued excessively, the solenoid will stick.

• The solenoid for the pump has failed.

• The shuttle valve for the clutch for that wheel has failed.

• The orifice in the port on the clutch control valve "C1" or "C2" on the control valve is plugged.

• The clutch for the gear group has failed. Check the clutch assembly. If necessary, replace the clutch assembly.

• The input shaft for the gear group has failed. This is unlikely.

• The control mechanism for the pump displacement has failed.

Problem: One of the wheels for the AWD system turns in one direction only.

Probable Cause

• The associated clutch solenoid has failed in the CLOSED position. This can be verified by using the override function in AVSpare Electronic Technician (ET). Overriding a clutch solenoid should cause the clutch pressure of the selected side to change from near 0 kPa (0 psi) to approximately 2000 kPa (290 psi).

• The pump control solenoid has failed. Verify using Cat ET.

• The shuttle valve for the clutch for that wheel has failed.

• The control mechanism for the pump displacement has failed.

Problem: One wheel locks up in one direction when the AWD system is OFF. The front wheel skids when the AWD system is OFF. The front wheel spins but the front wheel operates roughly when the AWD system is ON.

Probable Cause

• The opposite clutch has failed in the OPEN position. If the wheel locks up during forward operation, the reverse solenoid for that wheel has failed. If the wheel locks up during reverse operation, the forward solenoid for that wheel has failed.

• The clutch for the gear group has failed. Check the clutch assembly. If necessary, replace the clutch assembly.

Problem: The wheel speed surges when the AWD system is operating at high aggression settings. The engine speed surges when the AWD system is operating at high aggression settings.

Probable Cause

• If the machine is being operated in sand or in similar loose, dry conditions, reduce the aggression to a maximum of 100 percent. The stability control reduces this surging. The stability control may not eliminate the surging completely in extreme conditions.

Problem: During operation of the machine, the front wheels have a harsh disengagement when the AWD system is turned from the MANUAL mode to the OFF mode.

Probable Cause

• The charge pressure is too high. Check the charge pressure. If necessary, replace the relief valves.

• The AWD system is out of calibration. Use Cat ET in order to calibrate the system.

Problem: The front wheels lock up momentarily during shifts in direction.

Probable Cause

• The wiring connection for the clutch solenoid is reversed. Reversed wiring can also cause low clutch pressure during high aggression settings. Reversed wiring can also cause high clutch pressure during low aggression settings. Check the wiring connections.

• The clutch solenoid has failed. The clutch solenoid is sticking. Replace the clutch solenoid that has failed.

Problem: The AWD motors produce a loud noise during high speed operation ("5R", "6F", and "7F").

Probable Cause

• Check the clutch pressure.

• The front tire diameter is significantly larger than the rear tire diameter.

• Check the oil level in the front gear groups.

Problem: After switching to the CREEP mode with the transmission direction control in NEUTRAL, the machine begins to move very slowly. Otherwise, the system is functioning correctly. The AWD ECM does not show any active fault codes.

Probable Cause

• The neutral position for the pump for one or both of the pumps is out of adjustment.

Note: The control is capable of detecting inadvertent motion. In most cases, the control will disable the AWD clutches. The control will warn the operator before CREEP mode is engaged. When the speed of the motor is below the capability of the speed sensors, the speed may not be detected. A speed above 0.17 km/h (0.10 mph) should be detected by the AWD ECM. This will disable the AWD system until the problem is corrected and the machine is started again. Speeds that are lower than 0.17 km/h (0.10 mph) may not be detected.

Problem: In fourth speed forward on hard pavement, the maximum pressure from the all wheel drive piston pump cannot be set to 38000 kPa (5500 psi).

Probable Cause

• The internal relief valves for the all wheel drive piston pump are not functioning correctly.

• The high pressure relief valve in the control valve for the all wheel drive is set too low.

• The all wheel drive piston pump is worn, resulting in excessive internal leakage.

Problem: The AWD system overheats too quickly at low operating pressures.

Probable Cause

• The cooler bypass valve is not functioning correctly.

• The thermal bypass valve is not functioning correctly.

• The flow of hydraulic oil to the hydraulic oil cooler is obstructed.

• While the all wheel drive system is operating, the charge pressure is not correct.

• The all wheel drive piston pump is worn.

• The all wheel drive piston motor is leaking.

• The flow of air through the hydraulic oil cooler may be obstructed. Inspect the oil cooler and clean the oil cooler.

After the above listed problems have been resolved, the AWD system will need to be recalibrated. To ensure the proper function of the AWD system, use Cat ET to recalibrate the system.

Problem: The wheel speed or the engine speed surges when the AWD system is turned on. The aggression setting is not a factor.

Probable Cause

• The wheel sensors have failed. The wiring harness should be checked. If necessary, replace the wheel sensors.

• The AWD system is significantly out of calibration. Use Cat ET in order to perform system calibrations.

• Check the setting for the Pressure Override (POR) for the pump. Adjust the POR settings for the pump. Incorrect POR settings may cause the pump to become unstable.

• The adjustments to the pump or the adjustments to the motor have changed. Use Cat ET in order to perform a system calibration. The calibration sequence will automatically identify motor speeds that are out of the proper range.

ReferenceIf the speeds are out of the proper range, refer to AWD ECM Testing and Adjusting, "Pump Displacement Testing and Adjusting" for additional information. If the speeds are out of the proper range, refer to AWD ECM Testing and Adjusting, "Motor Displacement Testing and Adjusting" for additional information.

Problem: The oil level for the AWD gearbox is too full. The oil for the AWD gearbox is diluted with hydraulic oil.

• The shaft seal for the AWD motor has failed. Check the shaft seal for the AWD motor. If necessary, replace the shaft seal.

• The clutch piston seals inside the gearbox may be leaking. Check the clutch piston seals. If necessary, replace the clutch assembly.

Problem: The AWD system is functioning. The green indicator light is operating normally. The wheels do not spin. There is no AWD motor speed indicated by Messenger.

• Check for low charge pressure

• Check the gear drive for the pump. Verify that the pump is operating with the engine.

Problem: The AWD system loses aggression momentarily during operation. A diagnostic for the speed sensor may be logged into the AWD ECM. Fault codes are not active during this event. High temperature derates are not active during the event.

• Check the speed sensors. If necessary, replace the speed sensors.

• Check the wiring for the speed sensors for an intermittent short. Check the wiring for the speed sensor for loose connections.

Problem: One of the front wheels is not pulling and the steering system generates "Low Main Pump Pressure" fault when changing the steering angle.

The fault occurs only when the machine is operated with the AWD system at high aggression in gears "1F" through "4F" or in gears "1R" through "3R". The implement pump pressure will remain low or the pump pressure will decrease when the following conditions are met:

• The machine is traveling in "1F" through "4F".

• The AWD system is set to maximum aggression.

• The machine is steered in the direction of the suspect wheel.

Steering the machine in the opposite direction of the suspect wheel will cause the implement pump pressure to increase above standby pressure.

Probable cause

• A clutch solenoid had failed. Perform the AWD Testing and Adjusting, "Solenoid Valve (Control Manifold) - Test". If necessary, replace the solenoids.

• A solenoid for the pump has failed. Perform the AWD Testing and Adjusting, "Solenoid Valve (Pump Displacement) - Test". If necessary, replace the solenoids.

• The clutch for the suspect wheel has failed or the clutch has been incorrectly installed. Inspect the clutch. If necessary, replace the clutch.

• The input shaft for the gearbox is broken. This is unlikely. Replace the input gear assembly.

• The output shaft for the wheel motor is broken. This is unlikely. Replace the motor.

Problem: One of the front wheels is not turning. All of the clutch solenoids are operating correctly. The motor output speed is detected by using Cat ET.

Probable cause

• There is debris that is plugging the orifice for the clutch at the control valve. The ports are marked "CR" or "CL". Clean the orifice or replace the orifice. Locate the source of the debris.

• The clutch assembly has been incorrectly installed. The clutch assembly may be installed 180 degrees out of the correct position. Remove the clutch assembly in order to ensure that the port in the wheel housing is aligned with the passage in the clutch assembly.

• The clutch assembly has failed. Inspect the clutch assembly. If necessary, replace the clutch assembly.

• The coupling between the motor and the gearbox is missing. Replace the coupling.

• The input shaft for the gearbox is broken. This is unlikely. Replace the input gear assembly.

• The output shaft for the wheel motor is broken. This is unlikely. Replace the motor.