GM Service Manual Online
For 1990-2009 cars only

Important: 

   • Perform the Diagnostic System Check - Vehicle before using the symptom tables in order to verify that all of the following are true:
      - There are no diagnostic trouble codes (DTCs) present.
      - The control module or 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 for system operation.

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 be the cause of 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:

    •  Service Indicator Always On
    •  Service Indicator Inoperative
    •  Transfer Case Popping Noise
    •  Transfer Case Whine or Rumble Noise
    •  Transfer Case Grating Noise
    •  Transfer Case Clunk During Acceleration and Deceleration
    •  Transfer Case Shudder or Binding
    •  Transfer Case Leak Diagnosis