Chevrolet Silverado / GMC Sierra. Manual — part 2877
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
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
Transfer Case Control Schematics
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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