Circuit/System Testing
WARNING: This page is about a different car, the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The Ignition 1 voltage circuit and the axle actuator control circuit must be tested for opens, shorts to ground, shorts to voltage, and high resistance. This can also result from a electrically faulted actuator.
- With the ignition on check which DTC is set. If DTC C0379 is set with failure type byte 08 then do the following.
- Shift the vehicle into 4 high and look at the scan tool data list to see if the front axle actuator is engaging. If the axle actuator can be heard engaging but the scan tool still indicates disengaged then check the axle switch signal circuit for an open or high resistance. Shift the vehicle to 2 high, if the scan tool indicates the axle actuator is engaged then check the axle switch signal for a short to voltage. If everything checks out go to the next step.
- Remove the front axle actuator and try to shifting from 4WD to 2WD and see if the states change.
- If the states change then inspect the front axle for mechanical conditions. Refer to Four-Wheel Drive Does Not Engage or Four-Wheel Drive Does Not Disengage . If this checks out then go to the next step.
- Disconnect the connector at the front axle actuator and check for battery voltage on the ignition 1 circuit. Also check the front axle actuator ground for proper connections.
- If these circuit test bad repair as necessary checking inline connectors X110 and X109. If these circuits test good go to the next step.
- Check the axle actuator control circuit for an open, short to ground, or short to voltage.
- If the actuator control circuit checks good, then short the actuator control circuit to ground at the transfer case control module connector X1 pin 15. This should cause the actuator to engage, remove the ground and then reinstate the ground and the actuator should disengage. If the front axle actuator engages and disengages then replace the transfer case control module, program, and complete the motor learn procedure. If it does not fully engage or disengage then replace the front axle actuator.