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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 If the value is less than 1,420 ohms, test the VSS high signal and the VSS low signal 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 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 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 Inspect the easily accessible or visible system components for obvious damage or conditions Inspect the automatic transfer case for the proper fluid level. Intermittent Faulty electrical connections or wiring may cause intermittent conditions. Refer to Testing for Symptom List Refer to a symptom diagnostic procedure from the following list in order to diagnose the Front Axle Will Not Engage Front Axle Will Not Disengage IMPORTANT: Perform the Diagnostic System Check - Vehicle before using There are no diagnostic trouble codes (DTCs) set. The control modules can communicate via the serial Review the system operation in order to familiarize yourself
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 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
The front axle control circuit, which is also connected to the transfer case shift control The front axle switch circuit, which is also connected to the transfer case shift control 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 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
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