Chevrolet Silverado / GMC Sierra. Manual — part 2918

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 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.

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.

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.

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

2008 Chevrolet Silverado 1500

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

Silverado

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 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

DTC C0387

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 C0387 59

Unable to Complete Shift Circuit/Component Protection Timeout

Diagnostic Fault Information

Circuit/System Description

The transfer case control module commands shifts through motor A and motor B control circuits
causing the transfer actuator to shift the transfer case to different modes or ranges depending on
driver selection. If the shift lever detent shaft were to bind, or there was a mechanical failure, or
motor A control and motor B control were shorted together the shift would not be completed.
This will cause the DTC to set in order to protect system components from damage.

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Circuit/Component

Timeout

Unable to Complete Shift

-

-

-

DTC C0387 59

2008 Chevrolet Silverado 1500

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

Silverado

Conditions for Running the DTC

The ignition is ON.

System voltage is 10.5-18 volts.

Conditions for Setting the DTC

A shift request was received but could not be completed within 15 seconds causing this DTC to
set.

Action Taken When the DTC Sets

All shifting is disabled until condition is corrected.

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

Component Connector End Views

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

2008 Chevrolet Silverado 1500

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

Silverado

Scan Tool Data List

Scan Tool Data Definitions

Diagnostic Aids

Motor control A shorting to motor control B could cause this DTC.

Circuit/System Testing

1. Ignition off with a DMM check to see if motor A control and motor B control are shorted

together after disconnecting the transfer case control module and the transfer case actuator.

If motor A control is shorted to motor B control repair circuits as necessary. If the
circuits checked good go to next step.

2. Remove the transfer actuator and check to see if the shift detent shaft is binding.

If the shift lever detent shaft is binding refer to Transfer Case Disassemble. If the
shift lever detent shaft is not binding replace the transfer case actuator.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Transfer Case Two/Four Wheel Drive Actuator Replacement

Transfer Case Disassemble

DTC C0392

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 C0392 01

Rotational Position Sensor Circuit Short to Battery

DTC C0392 02

Rotational Position Sensor Circuit Short to Ground

2008 Chevrolet Silverado 1500

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

Silverado