GM Service Manual Online
For 1990-2009 cars only

Important: 

   • Perform the Diagnostic System Check - Transfer Case before using the symptom tables in order to verify that the following statements are true:
      - No diagnostic trouble codes (DTCs) are 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 in Wiring Systems.
    • 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 in Wiring Systems.

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
    •  Accessory Switch Transfer Case Mode Buttons Inoperative
    •  Service Four-Wheel Drive Indicator Always On
    •  Service Four-Wheel Drive Indicator Inoperative
    •  Accessory Switch Transfer Case Mode Indicator Always On - Two or More
    •  Accessory Switch Transfer Case Mode Indicator Flashes, then Returns to Previous Mode
    •  Accessory Switch Transfer Case Mode Indicator Inoperative - One or More
    •  Accessory Switch Transfer Case Mode Indicator Flashes in 2WD Mode
    •  Accessory Switch Transfer Case Mode Indicator Flashes in 4WD High or 4WD Low Mode
    •  Accessory Switch Transfer Case Mode Indicator Flashes in 4WD High, 4WD Low, and 2WD Modes
    •  Accessory Switch Transfer Case Mode Indicator Flashes in Neutral Mode
    •  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 Shudder or Binding
    •  Transfer Case Will Not Shift
    •  Transfer Case Jumps Out of Gear