Rear Drive Axle Description and Operation

The rear differential assembly in this vehicle consists of an aluminum housing which contains a electric clutch/coupler and a differential. The differential fluid is only contained in the differential housing portion.

The clutch and clutch housing are serviced as an assembly. The fluid level range for proper rear differential assembly operation is 500 ml. New service replacement units will be shipped dry (without fluid). Fill new units with 500 ml of GL Synthetic fluid.

Fig 1: Rear Drive Axle Block Diagram

Courtesy of GENERAL MOTORS COMPANY

The rear drive axle system operates as follows:

• The system distributes torque to the rear wheels to enhance traction and improve vehicle handling performance.
• The all wheel drive (AWD) clutch assembly contains an electromagnetic coil, primary clutch, a ball cam, a secondary clutch, and a rear differential clutch control module.
• The rear differential clutch control module uses wheel speeds, steering angle, lateral acceleration, yaw, chassis control intervention, and other signals to determine the torque to be applied. This data is transmitted via the vehicles Controller Area Network (CAN) from other modules and sensors in the vehicle.
• The driver information center can display two messages for the Rear Drive Axle system. Service All Wheel Drive or code 73 and AWD Off or code 173. When these messages are displayed, the system is disabled and the vehicle will default to 2wd.
• If the vehicle is being driven very aggressively or an unexpected tire size has been used, the AWD Off or code 173 message will be displayed in the driver information center. This should not result in the replacement of rear differential clutch control module.
• The AWD Off or code 173 message will be displayed in the driver information center if the mini-spare tire or a very small sized tire has been installed. This should not result in the replacement of rear differential clutch control module.
• The torque transfer to the rear wheels is controlled by the rear differential clutch control module which sends current to the electromagnet coil in the clutch. The coil applies a load on the primary clutch which rotates the ball cam loading the secondary clutch. The secondary clutch applies the torque from the drive shaft, driving the rear wheels. Safe current range is between 0-6.0 A. If the current is out of the specified range, a DTC will be set, and the driver information center will display the Service AWD or code 73 message.
• The rear differential clutch control module has an internal temperature sensor, which will maintain consistent and continuous temperature compensation for torque transfer from -40°C to +120°C. When the temperature of the module is determined to be beyond its limits, the rear differential clutch control module will temporarily disable the rear drive system and the driver information center will display the AWD Off or code 173 message. When the temperature of the module is back within the limits, the rear differential clutch control module will enable the rear drive system.
• The rear differential clutch control module monitors the outside air temperature maintaining consistent and continuous temperature compensation for torque transfer from -20°C (-4°F) to 100°C (212°F).
• Voltage to the module is between 9-16 V. The module will set a low voltage DTC and a high voltage DTC to indicate voltage value out of range.
• If replacing the rear differential assembly or the rear differential clutch control module, the module needs to be configured for the clutch control calibrations. The rear differential housing will have a 1 digit code on it. The 1 digit code must be programmed into the rear differential clutch control module using the scan tool.