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 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 .

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
    •  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