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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Denali 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC C0379

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

DTC Descriptor

DTC C0379 01: Front Axle System Short to Battery

DTC C0379 02: Front Axle System Short to Ground

DTC C0379 04: Front Axle System Open Circuit

DTC C0379 08: Front Axle System Signal Invalid

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Invalid

Front Axle System

DTC C0379 02

DTC C0379 04

DTC C0379 01

DTC C0379 08

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:

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

When a shift to AUTO 4WD, 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.

This DTC detects a short to ground, short to voltage or an open circuit.

Conditions for Running the DTC
    • The ignition is ON.
    • System voltage is 10.5-18 volts.

Conditions for Setting the DTC
    • This DTC sets if the front axle actuator switch shows battery voltage when the actuator is disengaged, or when the front axle actuator shows no voltage when the actuator is engaged.
    • The module also monitors the axle actuator control circuit and sets the DTC if a high voltage is expected (disengaged) and a low voltage is seen. It will also set when a low voltage is expected (engaged) and a high voltage is seen.

Action Taken When the DTC Sets
    • The front axle may be engaged at all times or disengaged at all time depending on the failure type.
    • The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
    • A history DTC clears after 40 consecutive warm up cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Reference Information

Schematic Reference

Transfer Case Control Schematics

Connector End View Reference

Transfer Case Control Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

DTC Symptom Description

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Testing

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.

  1. With the ignition on check which DTC is set. If DTC C0379 is set with failure type byte 08 then do the following.
    2. ⇒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.
  2. Remove the front axle actuator and try to shifting from 4WD to 2WD and see if the states change.
    3. ⇒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.
  3. 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.
    4. ⇒If these circuit test bad repair as necessary checking inline connectors X110 and X109. If these circuits test good go to the next step.
  4. Check the axle actuator control circuit for an open, short to ground, or short to voltage.
    5. ⇒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.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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