Diagnostic Trouble Code (DTC) C0379 Set, Service 4WD Light On, 4WD Inoperative (Replace Front Axle Actuator)

Some customers may comment that the Service 4WD light is on and/or the 4WD system will not engage. This condition may only occur after a cold temperature start-up (typically below -6°C to -1°C (20°F to 30°F).

If this concern is accompanied by an illuminated "Service 4WD" light, and a DTC C0379, during a cold weather start up, the following information may apply.

The front drive axle actuator assembly engages the front axle in response to commands from the Transfer Case Control Module (TCCM). Normally, the cycle time for engagement is under 3 seconds, regardless of temperature. If the actuator does not engage the front axle assembly within 10 seconds, the TCCM sets DTC C0379, illuminates the "Service 4WD" light and disables the 4WD system. There have been reports of vehicles with front drive axle actuator assemblies that take longer than 10 seconds to engage, setting this code.

Important: When a vehicle with this concern is diagnosed in the repair facility, usually the inside temperature is warm enough that the system operates normally, and the C0379 will be set as a history code, making the concern intermittent and difficult to diagnose.

Follow the service procedure below to replace the front axle actuator.

1. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information. Refer to Lifting and Jacking the Vehicle (SI Document ID #744862).
2. Remove the engine shield mounting bolts.
3. Remove the engine shield.
4. Disconnect the electrical connector from the actuator assembly.



5. Remove the actuator assembly bolts.
6. Remove the actuator assembly.
7. Install the new actuator assembly, P/N 12471631.

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

8. Install the actuator assembly bolts.

Tighten
Tighten the bolts to 6 N·m (53 lb in).

9. Connect the electrical connector to the actuator assembly.
10. Install the engine shield.
11. Install the engine shield mounting bolts.

Tighten
Tighten the engine shield mounting bolts to 25 N·m (18 lb ft).

12. Lower the vehicle and test.

DO NOT order parts for stock. Parts are in LIMITED quantities at GMSPO.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: