Four Wheel Drive (4WD) Systems

Four Wheel Drive (4WD) Systems

Principles of Operation

The vehicle is equipped with an All-Wheel Drive (AWD) system that is always active and requires no driver input. The system does not have a Mode Select Switch (MSS).

All AWD (All-Wheel Drive) control logic resides in the PCM. The PCM continuously calculates if torque is required at the rear wheels and when torque is required, sends a low-current signal Pulse-Width Modulation (PWM)) to the AWD (All-Wheel Drive) relay module over a hard wired circuit. The AWD (All-Wheel Drive) relay module then outputs a high-current PWM (Pulse-Width Modulation) signal which varies the current and duty cycle sent to the Active Torque Coupling (ATC) device, which is located inside the rear axle.

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 PWM (Pulse-Width Modulation) current supplied to the ATC (Active Torque Coupling) device increases as demand for rear wheel torque increases. The AWD (All-Wheel Drive) relay module returns a signal to the PCM throughout AWD (All-Wheel Drive) operation to system monitoring capabilities to the PCM over hard a wired circuit.

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 acceleration, the PCM commands torque delivery 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.

A spare tire of a different size other than the tire provided should never be used. A dissimilar spare tire size (other than the spare tire provided) or major dissimilar tire sizes between the front and rear axles could cause the AWD (All-Wheel Drive) system to stop functioning correctly. If the incorrect spare tire or dissimilar tire sizes between the front and rear axles is installed, the AWD (All-Wheel Drive) system disables automatically and enters Front Wheel Drive (FWD) only mode to protect driveline components. This condition could 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 message should disappear 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.

AWD (All-Wheel Drive) faults are 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 PCM 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.

The active, on-demand AWD (All-Wheel Drive) system uses data from other systems as inputs to the PCM. The PCM uses the inputs to determine the appropriate duty cycle to send to the AWD (All-Wheel Drive) relay module and ATC (Active Torque Coupling) solenoid that delivers the desired torque to the rear wheels. Specific inputs to the PCM are:

- Steering wheel angle from the Steering Column Control Module (SCCM) via the High Speed Controller Area Network (HS-CAN)

- Yaw rate and Lateral acceleration from the Restraints Control Module (RCM) 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)

- AWD (All-Wheel Drive) relay module diagnostic

PCM outputs are:

- Solid-state clutch (PWM (Pulse Width Modulated) signal) to the AWD (All-Wheel Drive) relay module

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

Heat Protection Mode

The All-Wheel Drive (AWD) system utilizes a heat protection mode to protect the Power Transfer Unit (PTU) and the Active Torque Coupling (ATC) solenoid from damage due to heat build up caused by clutch slippage while driving in extremely slippery road conditions. If the AWD (All-Wheel Drive) system detects an overheat condition, it increases the duty cycle to keep the clutches from slipping. If the heat in the system continues to rise, the AWD (All-Wheel Drive) relay 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 system to cool down at least 10 minutes with the ignition ON (RUN). For concerns with the PTU (Power Transfer Unit), refer to Transfer Case.