Chevrolet Silverado / GMC Sierra. Service manual — part 2925

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.

Reference Information

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

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 Procedures

2008 Chevrolet Silverado 1500

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

Silverado

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

FRONT AXLE WILL NOT DISENGAGE

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.

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.

Reference Information

Schematic Reference

2008 Chevrolet Silverado 1500

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

Silverado

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

1. If this is occurring without DTC C0379 setting it is likely related to a mechanical issue.

Refer to Four-Wheel Drive Does Not Disengage .

2. If no mechanical issue is found replace the front axle actuator.

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

Four-Wheel Drive Does Not Engage

Four-Wheel Drive Does Not Disengage

Front Drive Axle Actuator Replacement

TRANSFER CASE SHIFT CONTROL SWITCH INOPERATIVE

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 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The active transfer case mode switch circuit consists of 5 modes. The transfer case shift control
module supplies 5 volts to the switch through the 5-volt reference circuit. The current travel
through the resistor of the currently active mode. The current is then returned to the transfer case
shift control module through the switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage to determine the
condition of the mode switch circuit.

When each of the modes are selected they complete a circuit through their own specific resistor.
The transfer case shift control module continuously monitors the switch input to determine
whether the Neutral, AWD, 2HI, 4HI, or 4LO mode was selected by the driver.

Reference Information

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

Diagnostic Aids

If the 5-volt reference or the switch signal wire are shorted to ground the scan tool can show up

2008 Chevrolet Silverado 1500

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

Silverado