Chevrolet Silverado / GMC Sierra. Service manual — part 2877

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Raise and support the drive wheels.

2. Start and idle the engine.

3. Place the transmission in DRIVE.

4. Monitor VSS on the scan tool under engine data.

5. The VSS on the scan tool should be greater than 100 RPM.

Circuit/System Testing

1. Measure the resistance between the VSS high signal circuit and the VSS low signal circuit.

The resistance should be between 1,420-2,140 ohms.

If the value is greater than 2,140 ohms, test the VSS high signal circuit and the VSS
low signal circuit for an open.

If the value is less than 1,420 ohms, test the VSS high signal and the VSS low signal
circuits for a shorted together condition.

2. Measure the resistance of the VSS high signal circuit to ground. The resistance should be

greater than 10M ohms.

If the value is less than 10M ohms, repair the short to ground.

3. Measure the resistance between the VSS low signal circuit and ground. The resistance

should be greater than 10M ohms.

If the value is less than 10M ohms, repair the short to ground.

4. Reconnect the ECM connector. Disconnect the VSS connector. Ignition ON, test the ISS

high signal circuit for a short to voltage.

If all circuits/connections test normal, test or replace the VSS.

5. If all previous steps for circuit checking and VSS replacement have been made and all

component testing has been performed and the condition persists replace the ECM.

Component Testing

1. Verify the VSS resistance is within the specified range.

2008 Chevrolet Silverado 1500

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

Silverado

2. Using a terminal test kit, connect the DMM between the VSS high signal and the VSS low

signal circuits at the VSS connector. Raise and support the drive wheels. While rotating the
drive wheels by hand ensure the AC voltage reading on the DMM is above 0.4 volts.

If the AC voltage is not above 0.4 volts, replace the VSS.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Ensure that the VSS is 500 RPM or greater for 3 seconds and does not change more than
500 RPM or greater for 3 seconds.

Vehicle Speed Sensor Replacement

Control Module References for ECM replacement, setup, and programming.

SYMPTOMS - TRANSFER CASE

Review the system operation in order to familiarize yourself with the system functions.
Refer to Transfer Case Description and Operation.

Inspect the easily accessible or visible system components for obvious damage or conditions
which could cause the symptom.

Inspect the automatic transfer case for the proper fluid level.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to
Testing for Intermittent Conditions and Poor Connections . Some symptoms may be caused
by loose wiring. Test the system after moving or connecting harnesses, but before replacing parts.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the
symptom:

IMPORTANT: Perform the Diagnostic System Check - Vehicle before using the

symptom tables, in order to verify the following conditions are
true:

There are no diagnostic trouble codes (DTCs) present.

The control modules can communicate via the serial data
link.

2008 Chevrolet Silverado 1500

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

Silverado

Front Axle Will Not Engage

Front Axle Will Not Disengage

Transfer Case Shift Control Switch Inoperative

Transfer Case Shift Control Switch Indicator Always On - Two or More

Transfer Case Shift Control Switch Indicator Inoperative - One or More

Service Indicator Always On

Transfer Case High/Low Clutch Reset

Transfer Case Popping Noise

Transfer Case Whine or Rumble Noise

Transfer Case Growl or Grinding Noise

Transfer Case Clunk in 2HI Only

Transfer Case Clunk in 4HI

Transfer Case Clunk in 4LO

Transfer Case Will Not Shift

Transfer Case Jumps Out of Gear

Transfer Case Leak Diagnosis

FRONT AXLE WILL NOT ENGAGE

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

2008 Chevrolet Silverado 1500

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

Silverado

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 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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

2008 Chevrolet Silverado 1500

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

Silverado