Principles of Operation
The AWD system is an active system, which means it not only responds to wheel slip between the front and rear axles but also has the ability to anticipate wheel slip and transfer torque to the rear wheels before the slip occurs. The AWD system is active all the time and requires no input from the operator.
The AWD system continuously monitors vehicle conditions and automatically adjusts the torque distribution between the front and rear wheels. During normal operation, most of the torque is delivered to the front wheels. If wheel slip between the front and rear wheels is detected, if the vehicle is under heavy acceleration or if the vehicle is in an aggressive handling event, the AWD system increases torque to the rear wheels to prevent or control wheel slip. When the AWD system is functioning properly, there should be no perceived speed difference between the front and rear axles when launching or driving the vehicle on any uniform surface. Traction should be similar to a part time 4WD system in 4H (4X4 HIGH), but have no binding in turns.
If the compact spare tire is installed, the AWD system may disable automatically and enter FWD only mode to protect driveline components. This condition may be indicated by an AWD OFF message in the message center.
If there is an AWD OFF message in the message center from using the compact spare tire, this indicator should turn off after reinstalling the repaired or replaced normal road tire and cycling the ignition OFF and ON. It is recommended to reinstall the repaired or replaced road tire as soon as possible. Major dissimilar tire sizes between the front and rear axles could cause the AWD system to stop functioning and default to FWD or damage the AWD system.
AWD faults may be indicated by the powertrain malfunction (wrench) message center warning indicator in the IPC as well as the Check AWD message center warning indicator in the message center.
The AWD system consists of a PTU, driveshaft, front and rear halfshafts, AWD relay, PCM which includes the AWD control logic and an ATC solenoid located in the rear axle. Based on inputs to the PCM, the PCM sends a command to the AWD relay. The amount of torque sent to the rear wheels is controlled by the AWD relay sending a PWM duty cycle to the ATC solenoid.
The PCM also provides the brake system with its current clutch duty cycle and determines weather or not the brake system may take command of the clutch duty cycle.
Specific inputs to the PCM are:
- Accelerator pedal position via the High Speed CAN
- TR via the High Speed CAN
- Brake system status from the ABS module via the High Speed CAN
- Wheel speed from all 4 wheels from the ABS module via the High Speed CAN
PCM outputs are:
- Solid-state clutch PWM signal to the ATC solenoid
- Percent of torque transfer commanded signal to the ABS module via the High Speed CAN
- Torque request available signal to the ABS module via the High Speed CAN
Heat Protection Mode
During very extreme off-road operation, the AWD system utilizes a heat protection mode to protect the ATC solenoid from damage. If the AWD system detects an overheat condition, it enters a locked mode. If the heat in the AWD system continues to rise once in the locked mode, the PCM disables the ATC solenoid. This condition may be indicated by an AWD OFF message in the message center. To resume normal AWD function as soon as possible, stop the vehicle in a safe location and stop the engine for at least 10 minutes. After the engine is restarted and the AWD system has adequately cooled down, the AWD OFF message will turn off and normal AWD operation will return. In the event the engine is not stopped, the AWD OFF message will turn off when the system cools and normal AWD operation returns.
AWD Bar Code Identification
The AWD system on this vehicle is equipped with a bar coded ATC solenoid to reduce the tolerance of electrical current to torque delivered by the ATC solenoid. The ATC solenoid bar code can be found etched on the ATC solenoid wire harness connector protruding from the top of the rear drive axle or on the RDU. The PCM uses this bar code information to match the clutch characteristics of the ATC solenoid with the desired output torque. If the bar code information does not match the PCM information, driveline damage or driveability concerns can occur. Therefore, if the PCM needs to be replaced, the new PCM needs to be configured with the existing ATC solenoid bar code information. If the rear drive axle need to be replaced, the existing PCM will need to be configured with the new ATC solenoid bar code information. Carry out the AWD Drive Cycle.
Steel Cover RDU
Aluminum Cover RDU
| Item | Description |
|---|---|
| 1 | ATC solenoid bar code |
AWD Drive Cycle
Carry out the AWD drive cycle after downloading the ATC solenoid bar code information to the PCM.
- Carry out 3 accelerations from 0-48 km/h (0-30 mph) in a straight line.
- Perform this procedure at low, medium and full accelerator pedal position.
- Verify that there is no perceived front wheel slip.
- On dry pavement, drive the vehicle at 8 km/h (5 mph) in a fully locked turn.
- Verify that there is no driveline binding.