Chevrolet Silverado / GMC Sierra. Service manual — part 2872

resistance, and shorts to voltage by following the below listed steps.

1. With the ignition off disconnect connector X3 from the transfer case control module, and

also disconnect the connector at the transfer case actuator.

With a DMM check the motor A control and motor B control circuits for an open,
high resistance, or short to ground and repair as necessary. If all check good go to the
next step.

2. Connect X3 at the transfer case control module and turn on the ignition.

3. Check to motor A control and motor B control circuits for a short to voltage. If the circuits

shows to indication of a short to voltage go to component testing.

Component Testing

1. Turn the ignition off and check the motor windings for an internal short to ground inside the

motor by probing either the motor A control pin and taking the other lead to ground, or the
same can be done using motor B control pin. Motor control A is pin A and motor B control
is pin D.

If the DMM indicates and short to ground replace the transfer case actuator. If nothing
is found continue to the next step.

2. With a DMM check the resistance of the motor windings by probing pin A and pin D on the

transfer case actuator.

The DMM should indicate 0.3-40 ohms, if it does not replace the transfer case actuator
and complete the motor learn procedure. If the actuator is within specifications then
replace the transfer case control module, program, and complete the motor learn
procedure.

Repair Procedures

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

Transfer Case Two/Four Wheel Drive Actuator Replacement

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.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

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/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

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Front Axle System

DTC C0379

02

DTC C0379

04

DTC C0379
01

DTC C0379

08

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

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

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Scan Tool Data Definitions

Diagnostic Aids

When the circuits operating the lock solenoid are not complete the lock is engaged. When the
circuit is completed the lock is disengaged.

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:

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.

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.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado