GM Service Manual Online
For 1990-2009 cars only

Important: 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 Manual Selectable 4-Wheel Drive System. Refer to Checking Aftermarket Accessories in Wiring Systems.
    • Inspect the easily accessible, or the visible system components for obvious damage or conditions which could cause the symptom.
    • Ensure all mechanical components are operative before diagnosing the electrical portion of the system.
    • In order to determine whether the vehicle is in 2-wheel drive (2WD) or 4-wheel drive (4WD), lift the vehicle so that the wheels can spin freely. With the transfer case control lever in 2HI, turn the rear propshaft. If the front propshaft does not move with the rear, the vehicle is in 2HI. If the tires and the front propshaft moves, the transfer case is actually in 4WD.
    •  Make sure that the 4WD fuse is not open. If open, locate and repair the source of the overload. Refer to Testing for Short to Ground in Wiring Systems. Replace the fuse.

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:

    •  Four-Wheel Drive Does Not Disengage
    •  Four-Wheel Drive Does Not Engage
    •  Four-Wheel Drive Indicator Inoperative
    •  Four-Wheel Drive Indicator Always On
    •  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
    •  Transfer Case Leak Diagnosis