Four-Wheel Drive Systems - Overview: Notes

NOTE: The AWD system may be referred to as a 4WD system or Active Torque Coupling (ATC) system in other service information, owner literature, or messages located on the message center.

The AWD system consists of the following:

Power Transfer Unit (PTU)
Rear halfshafts
Driveshaft
AWD relay module
Rear Drive Unit (RDU)
Active Torque Coupling (ATC) solenoid (integral to the Rear Drive Unit (RDU)
PCM for system control logic

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, the vehicle is under heavy acceleration or if the vehicle is in a handling event, the AWD system increases the duty cycle to the Active Torque Coupling (ATC) solenoid. The ATC solenoid engages a pilot clutch in the Rear Drive Unit (RDU) which in turn sets a ball ramp device in motion. The ball ramp device applies the main clutch pack in the RDU and increases torque to the rear wheels as necessary. 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 operating in 4H (4X4 HIGH), but have no binding in turns.