Chevrolet Silverado / GMC Sierra. Service manual — part 2917

The general system performance DTC sets based on a thermal module within the transfer case
shift control module software. The components included in this thermal model are the motor
driver within the transfer case shift control module, the shift motor, and the clutch inside the
transfer case.

The General System Performance includes the following components:

The transfer case shift control module

The transfer case clutch

The transfer case shift motor

This fault occurs when one of the three components included in the thermal model surpass the
upper limits of this model indicating possible damage to the transfer case or other driveline
components. This DTC detects an over temperature condition base on a thermal model.

Conditions for Running the DTC

The ignition is ON.

System voltage is 10.5-18 volts.

DTC C0896 is not set.

Conditions for Setting the DTC

This DTC sets if one of three components: motor driver inside the transfer case shift control
module, transfer case clutch, or the shift motor, exceed the thermal model within the software for
the module.

Action Taken When the DTC Sets

All range and mode changes will be disabled while the DTC is current.

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 and current DTCs can be cleared using a scan tool.

Reference Information

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Schematic Reference

Transfer Case Control Schematics

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

Circuit/System Testing

The DTC can be set by more than one type of fault. It could be set by faulty wheel speed sensors,
a front axle actuator not mechanically engaging, a worn transfer case clutch, or a motor brake not
holding properly causing excessive motor engagement.

1. This system compares front wheel speeds to rear wheel speeds to determine if slip is

occurring and clutch engagement is necessary to correct this condition if the front axle
actuator has not mechanically engaged this slip correction can not happen and the DTC will
set.

Place the vehicle on a hoist, turn the ignition on, engine off and shift the transfer case
to 2WD. With a scan tool command the front axle actuator on using special functions
in the scan tool. While one person is holding one of the front tires still, spin the other
front tire if the front propshaft turns then the front axle is engaged. If it is engaged go
to the next step. If not, tear down and inspect the front axle clutch fork for mechanical
binding.

2. Using the scan tool, go into EBCM data display and find the front and rear.

Take the vehicle on a short test drive on a level and smooth surface. Compare the front
wheel speeds to the rear wheel speeds. If the wheel speeds are erratic or they drop out,

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

this would cause this DTC to set. Consider checking the EBCM for DTCs for the
wheel speeds. If the wheel speeds are erratic, use the DTC diagnostics in antilock
brakes to diagnose the condition. If this appears normal, to too the next step.

3. The next check will be to see if the motor brake is holding. If it does not, this will cause the

motor to stay engaged for extended periods of time causing it to exceed the thermal model.

With a scan tool clear the DTC, shift the vehicle to 2WD, and monitor the transfer case
motor amperage using the data display. Shift the vehicle to the 4 high mode if the
amperage goes up while the motor is shifting and goes back to 0 amps in 5 seconds or
less then the brake is holding. If the amperage stays high longer, this indicates the
brake is not holding and the actuator will need to be replaced. If the brake holds, go to
the next step.

4. Next will be checking the transfer case clutch integrity.

Place the vehicle for 4 high and take it for a test drive. Clear the DTC if possible.
Monitor front and rear wheel speeds using the EBCM data display. Under heavy
acceleration, monitor the front and rear wheel speeds. If the front wheel speeds are
much lower, this indicates a weak clutch and a transfer case tear down and inspection
will be required. If all of the above check all check out good replace the transfer case
shift control module if the DTC continues to set and perform the motor learn
procedure/Transfer Case High/Low Clutch Reset.

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 for Motor Learn Procedure

Four-Wheel Drive Does Not Engage

Front Drive Axle Clutch Fork Inspection

Transfer Case Assembly 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.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

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

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

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

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado