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 system has no Mode Select Switch (MSS).

Two transmissions are used with AWD (All-Wheel Drive). Vehicles with a 3.0L engine have the 6F35 transmission, controlled by the PCM. Vehicles with the 3.5L engine use the Aisin AW21, which is controlled by a stand-alone Transmission Control Module (TCM).

The 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 sent to the front wheels. If wheel slip between the front and rear wheels is detected or if the vehicle is under heavy acceleration (high-throttle position), the AWD (All-Wheel Drive) system increases torque to the rear wheels to prevent or control wheel slip.

AWD (All-Wheel Drive) faults may be indicated in the message center by the wrench lamp as well as the CHECK AWD message.

The 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 ATC (Active Torque Coupling) 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 TCM (Transmission Control Module) or 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 Modulation (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 system detects an overheat condition, it enters a locked mode. If the heat in the system continues to rise once in the locked mode, the 4X4 control module disables the ATC (Active Torque Coupling) solenoid. Allow the system to cool down at least 10 minutes with the ignition switch in the ON position.