Chevrolet Silverado / GMC Sierra. Service manual — part 2924

DTCs P2160 and P2161 are Type B DTCs.

Diagnostic Aids

Inspect the rear internal gear teeth for damage.

Visually inspect the VSS for cracks or damage.

Ensure the VSS is properly torqued to the transfer case housing.

This diagnostic relates to the VSS located in the transfer case and not the OSS located
within the transmission.

Reference Information

Schematic Reference

Transfer Case Control Schematics

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Transfer Case Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

2008 Chevrolet Silverado 1500

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

Silverado

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.

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

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.

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

Visual/Physical Inspection

Inspect for aftermarket devices which could affect the operation of the automatic transfer
case system. Refer to Checking Aftermarket Accessories .

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 cause intermittent conditions. Refer to Testing for
Intermittent Conditions and Poor Connections .

Symptom List

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

Front Axle Will Not Engage

Front Axle Will Not Disengage

IMPORTANT:

Perform the Diagnostic System Check - Vehicle before using
the symptom tables in order to verify the following
statements are true:

There are no diagnostic trouble codes (DTCs) set.

The control modules can communicate via the serial
data link.

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

2008 Chevrolet Silverado 1500

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

Silverado

Transfer Case Shift Control Switch Inoperative

No Correction for Slip in All-Wheel Drive Mode

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 Grating Noise

Transfer Case Clunk in 2HI Only

Transfer Case Clunk in 4HI

Transfer Case Clunk in 4LO

Transfer Case Clunk during Acceleration and Deceleration

Transfer Case Shudder or Binding

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:

2008 Chevrolet Silverado 1500

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

Silverado