Principles Of Operation

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).

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 system increases torque to the rear wheels to prevent or control wheel slip.

If the spare tire is installed, the AWD system may disable automatically and enter Front Wheel Drive (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 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 system may stop functioning and default to FWD or damage to the AWD system could occur.

AWD faults may be indicated by the powertrain malfunction (wrench) message center warning indicator in the Instrument Cluster (IC) as well as the Check AWD message center warning indicator in the message center.

The system consists of a Power Transfer Unit (PTU), 4X4 control module, rear axle and a solenoid-actuated ATC 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 device, located inside the rear axle. For concerns with the PTU, 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 solenoid is not repairable. If a new component is required, the ATC solenoid and rear axle are installed as an assembly. Refer to Differential Assembly &/or Axle Shaft Assembly.

The active, on-demand AWD 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 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
- Brake system status from the ABS module via the HS-CAN
- Wheel speed from all 4 wheels from the ABS module via the HS-CAN

4X4 control module outputs are:

- Solid-state clutch (Pulse Width Modulated (PWM) signal) to the ATC solenoid
- Percent of torque transfer commanded signal to the ABS module via the HS-CAN
- Torque request available signal to the ABS module via the HS-CAN

Heat Protection Mode

During very extreme off-road operation, the AWD system utilizes a heat protection mode to protect the ATC 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 solenoid. This condition may be indicated by an AWD OFF message in the message center. Allow the system to cool down at least 10 minutes with the ignition switch in the ON position.

Active Torque Coupling (ATC) Bar Code

The AWD system on this vehicle is equipped with a bar coded ATC to reduce the tolerance of electrical current to torque delivered by the ATC. The ATC bar code can be found etched on the ATC 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 with the desired output torque. If the ATC bar code information does not match the 4x4 control module information, driveline damage or drivability 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 bar code information.