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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 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 IMPORTANT: Review the system operation in order to familiarize yourself with the system functions. Refer to Transfer Case Description and
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Inspect for aftermarket devices which could affect the operation of the manual selectable 4- Inspect the easily accessible or visible system components for obvious damage or conditions Ensure all mechanical components are operative before diagnosing the electrical portion of In order to determine whether the vehicle is in 2-wheel drive (2WD) or 4-wheel drive Ensure the 4WD fuse is not open. If the fuse is open, locate and repair the source of the Intermittent Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Symptom List Refer to a symptom diagnostic procedure from the following list in order to diagnose the Four-Wheel Drive Does Not Disengage Four-Wheel Drive Does Not Engage Four-Wheel Drive Indicator Always On Four-Wheel Drive Indicator Inoperative 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
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
FOUR-WHEEL DRIVE DOES 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 A permanent magnetic motor A worm gear controlled plunger A front axle switch An electronic control circuit The front axle actuator consists of the following circuits: An ignition 3 voltage circuit A ground circuit An axle actuator control circuit An axle switch signal circuit Whenever a shift to 4WD is selected, the transfer case switch engages the front axle by grounding Reference Information Schematic Reference Transfer Case Control Schematics Connector End View Reference Component Connector End Views Electrical Information Reference
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Circuit/System Verification 1. Place the vehicle in 2WD install a scan tool and using engine data 2 look at the display for 4WD signal. 2. Verify that the scan tool indicates that the vehicle is in 2WD. If the scan tool indicates that the vehicle is in 4WD go to circuit system testing. Circuit/System Testing 1. Check the axle switch signal circuit for a short to voltage. If everything checks normal then go to the next step. 2. Check the front axle actuator control circuit for a short to ground with the front axle actuator disconnected and the mode selection switch disconnected. If everything checks normal reconnect the mode selection switch and retest. If the Front Axle Actuator and Axle Testing Remove the actuator and attempt shift from 2WD to 4WD, if the actuator moves check the front If the actuator does not function properly then replace the front axle actuator. Repair Procedures Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Front Drive Axle Actuator Replacement Transfer Case Gear Indicator Switch Replacement Front Drive Axle Clutch Fork Inspection FOUR-WHEEL DRIVE DOES NOT ENGAGE Diagnostic Instructions
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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