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MP 3010-NP0 - Transfer Case




DTC C0379

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

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/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:

* An Ignition 1 voltage circuit

* An axle switch signal circuit

* An axle actuator control circuit

* A ground circuit

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

Conditions for Running the DTC

* Ignition ON.

* System voltage 10.5-18 V.

Conditions for Setting the DTC

The TCCM monitors the front axle switch signal circuit and the front axle actuator control circuit for unexpected voltages. The DTC sets if the TCCM detects a high voltage when a low voltage is expected or a low voltage when a high voltage is expected.

Action Taken When the DTC Sets

C0379 01 and C0379 04

* The front axle remains disengaged at all times.

* The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

C0379 02

* The front axle remains engaged at all times.

* The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

C0379 08

The front axle remains in current mode.

Conditions for Clearing the DTC

* The TCCM clears the DTC once the conditions for setting the DTC are no longer present.

* A history DTC clears after 40 consecutive warm up cycles without a fault present.

* History DTCs can be cleared using a scan tool.

Diagnostic Aids

The transfer case fill/drain plugs provide a good ground point.

Reference Information

Schematic Reference

Transfer Case Control Schematics MP 3010-NP0 - Transfer Case

Connector End View Reference

Component Connector End Views Connector End Views By Name

Electrical Information Reference

* Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Control Module References for scan tool information.

Special Tools

* EL-49741 - 9 V+ Power Source Harness

* EL-49742 - Battery Voltage B+ and Ground Source Harness

* J 35616 - GM-Approved Terminal Test Kit

Circuit/System Verification

1. Key ON, engine OFF. Parking brake applied. Transmission in Neutral. Install a scan tool.

2. While monitoring the Front Axle Actuator parameter of the Data Display function on the scan tool, shift the vehicle into 4WD HI. The front axle actuator parameter should display Active or Engaged. You should also be able to hear the axle actuator engaging.

3. Shift the vehicle into 2WD HI. The Front Axle Actuator parameter should display Inactive or Disengaged. You should also be able to hear the axle actuator disengaging.

Circuit/System Testing

Note: When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J 35616 - Kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.

1. Verify that the TRANS IGN1 fuse, underhood fuse block, is not open.

• If the TRANS IGN1 fuse is open, test the Ignition 1 voltage circuit, front drive axle actuator harness X1 pin C, for a short to ground.

2. Wheels blocked. Parking brake engaged. Transmission in Neutral.

3. Ignition ON, engine OFF. Install a scan tool.

4. Disconnect the X1 harness connector at the front drive axle actuator (FDAA).

5. Using the GY probe J 35616-2A, test for B+ (+0.0/-1.0 V) between the Ignition 1 voltage circuit, FDAA X1 harness pin C, and a good ground.

• If the voltage is less than the specified value, test the affected circuit for an open/high resistance or short to ground. If all circuits and connections test normal, test the TCCM for proper operation.

6. Using the GY probe J 35616-2A, test for B+ (+0.0/-1.0 V) between the Ignition 1 voltage circuit, FDAA X1 harness pin C, and the ground circuit, FDAA X1 harness pin E.

• If the voltage is less than the specified value, test the ground circuit for an open/high resistance or short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

7. Using the GY probes J 35616-2A, test for B+ (+0.0/-1.0 V) between the Ignition 1 voltage circuit, FDAA X1 harness pin C and the axle switch signal circuit, FDAA X1 harness pin A.

• If the voltage is less than the specified value, test the axle switch signal circuit for an open/high resistance, short to ground or short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

8. Using the GY probes J 35616-2A, measure the voltage between the front axle actuator control circuit, FDAA X1 harness pin B and a good ground, while commanding the front axle actuator ON and OFF using the Front Axle Actuator function of the Special Functions feature of the scan tool. When commanded to ON the voltage should read 0.0 V. When commanded to OFF the voltage should read 3.5-6.0 V.

• If the measured voltage is less than 3.5 V when commanded OFF, test the front axle actuator control circuit for an open/high resistance or short to ground. If all circuits and connections test normal, test the TCCM for proper operation.

• If the measured voltage is greater than 6.0 V when commanded ON, test the front axle actuator control circuit for a short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

9. Go to Front Drive Axle Actuator (FDAA) in Component Testing.

Component Testing

Front Drive Axle Actuator (FDAA)

1. Key OFF. Disconnect the X1 connector at the FDAA.

2. Remove the FDAA.

3. Connect the FDAA X1 connector. Position the FDAA so that it is visible from the side of the vehicle.

4. Using the Engage Front Axle function of the Special Function feature of the scan tool, command the front axle ON and OFF. When commanded ON the plunger on the FDAA should extend. When commanded OFF the plunger should retract.

• If the FDAA does not perform as described, replace the FDAA.

5. Refer to Front Axle Will Not Engage Front Axle Will Not Engage or Front Axle Will Not Disengage Front Axle Will Not Disengage.

Transfer Case Shift Control Module (TCCM)

1. Key OFF. Disconnect the X1 connector at the front drive axle actuator (FDAA).

2. Key ON, engine OFF. Install a scan tool.

Note: When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J 35616 - Kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.

3. Using the GY probe J 35616-2A, connect a test light between the Ignition 1 voltage circuit, FDAA X1 harness pin C and the front axle actuator control circuit, FDAA X1 harness pin B.

4. Using the Engage Front Axle function of the Special Function feature of the scan tool, command the front axle ON and OFF. When commanded ON the test light should illuminate. When commanded OFF the test light should turn OFF.

• If the TCCM does not perform as described, replace the TCCM.

5. Go to Circuit/System Verification.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Control Module References Control Module References for TCSCM replacement, setup, and programming

* Transfer Case High/Low Clutch Reset Transfer Case High/Low Clutch Reset

* Four-Wheel Drive Does Not Engage Four-Wheel Drive Does Not Engage

* Four-Wheel Drive Does Not Disengage Four-Wheel Drive Does Not Disengage

* Front Drive Axle Actuator Replacement Service and Repair

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