GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    â€¢ Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    â€¢ Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    â€¢  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator motor consists of a permanent magnetic motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit within the actuator assembly.

The front axle actuator consists of the following circuits:

    â€¢ The front axle control circuit, which is also connected to the transfer case shift control module
    â€¢ The front axle switch circuit, which is also connected to the transfer case shift control module
    â€¢ An ignition 3 voltage circuit
    â€¢ A ground circuit

When a shift to 4HI, or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle control circuit through a current limiting driver.

Reference Information

Schematic Reference

Transfer Case Control Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    â€¢  Circuit Testing
    â€¢  Connector Repairs
    â€¢  Testing for Intermittent Conditions and Poor Connections
    â€¢  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Testing

  1. If this is occurring without DTC C0379 setting it is likely related to a mechanical issue. Refer to Four-Wheel Drive Does Not Engage .
  2. If no mechanical issue is found replace the front axle actuator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    â€¢  Control Module References for TCSCM replacement, setup, and programming
    â€¢  Transfer Case High/Low Clutch Reset
    â€¢  Four-Wheel Drive Does Not Engage
    â€¢  Four-Wheel Drive Does Not Disengage
    â€¢  Front Drive Axle Actuator Replacement