Four Wheel Drive (4WD) Systems

Four Wheel Drive (4WD) Systems

Principles of Operation

The vehicle is equipped with an All-Wheel Drive (AWD) system, also referred to as Active Torque Coupling (ATC), that is always active and requires no driver input. The AWD (All-Wheel Drive) system has no Mode Select Switch (MSS).

The AWD (All-Wheel Drive) 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, or if the vehicle is under heavy acceleration, the AWD (All-Wheel Drive) system increases torque to the rear wheels to prevent or control wheel slip. When the AWD (All-Wheel Drive) 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 Four-Wheel Drive (4WD) system in 4H (4X4 HIGH), but have no binding in turns.

If the spare tire is installed, the AWD (All-Wheel Drive) system may disable automatically and enter Front Wheel Drive (FWD) only mode to protect driveline components. This condition may be indicated by an AWD (All-Wheel Drive) OFF message in the message center.

If there is an AWD (All-Wheel Drive) OFF message in the message center from using the spare tire, this indicator should turn off after reinstalling the repaired or replaced normal road tire and driving a short distance. It is recommended to reinstall the repaired or replaced road tire as soon as possible. If the sizes of the tires used on the front and rear axles differ greatly enough, the AWD (All-Wheel Drive) system may stop functioning and default to FWD (Front Wheel Drive) or damage to the AWD (All-Wheel Drive) system could occur.

AWD (All-Wheel Drive) faults may be indicated by the powertrain malfunction (wrench) message center warning indicator in the Instrument Panel Cluster (IPC) as well as the Check AWD (All-Wheel Drive) message center warning indicator in the message center.

The AWD (All-Wheel Drive) system consists of a Power Transfer Unit (PTU), 4X4 control module, rear axle and a solenoid-actuated ATC (Active Torque Coupling) device. Based on the amount of current sent to the clutch, the module varies the torque sent to the rear wheels by sending a duty cycle to the ATC (Active Torque Coupling) device, located inside the rear axle. For concerns with the PTU (Power Transfer Unit), refer to Transfer Case.

The 4X4 control module also provides the brake system with its current clutch duty cycle and determines whether or not the brake system may take command of the clutch duty cycle.

NOTE: The Active Torque Coupling (ATC) solenoid is not repairable. If a new component is required, the ATC (Active Torque Coupling) solenoid and rear axle are installed as an assembly.

The active, on-demand AWD (All-Wheel Drive) system uses data from other systems as inputs to the 4X4 control module. The 4X4 control module uses the inputs to determine the appropriate amount of current to send to the ATC (Active Torque Coupling) solenoid that delivers the desired torque to the rear wheels. Specific inputs to the 4X4 control module are:

- Accelerator pedal position via the High Speed Controller Area Network (HS-CAN)

- Transaxle range from the PCM via the HS-CAN (High Speed Controller Area Network)

- Brake system status from the ABS module via the HS-CAN (High Speed Controller Area Network)

- Wheel speed from all 4 wheels from the ABS module via the HS-CAN (High Speed Controller Area Network)

4X4 control module outputs are:

- Solid-state clutch (Pulse Width Modulated (PWM) signal) to the ATC (Active Torque Coupling) solenoid

- Percent of torque transfer commanded signal to the ABS module via the HS-CAN (High Speed Controller Area Network)

- Torque request available signal to the ABS module via the HS-CAN (High Speed Controller Area Network)

Heat Protection Mode

During very extreme off-road operation, the AWD (All-Wheel Drive) system utilizes a heat protection mode to protect the ATC (Active Torque Coupling) solenoid (part of rear axle) from damage. If the AWD (All-Wheel Drive) system detects an overheat condition, it enters a locked mode. If the heat in the AWD (All-Wheel Drive) system continues to rise once in the locked mode, the 4X4 control module disables the ATC (Active Torque Coupling) solenoid. This condition may be indicated by an AWD (All-Wheel Drive) OFF message in the message center. Allow the AWD (All-Wheel Drive) system to cool down at least 10 minutes with the ignition switch in the ON position.

Active Torque Coupling (ATC) Bar Code

The AWD (All-Wheel Drive) system on this vehicle is equipped with a bar coded ATC (Active Torque Coupling) to reduce the tolerance of electrical current to torque delivered by the ATC (Active Torque Coupling) solenoid. The ATC (Active Torque Coupling) bar code can be found etched on the ATC (Active Torque Coupling) wire harness connector protruding from the top of the rear drive axle. The 4X4 control module uses this bar code information to match the clutch characteristics of the ATC (Active Torque Coupling) with the desired output torque. If the bar code information does not match the 4X4 control module information, driveline damage or driveability concerns can occur. Therefore, if the 4X4 control module or the rear drive axle needs to be replaced, the 4X4 control module will need to be configured with the ATC (Active Torque Coupling) bar code information.