GM Service Manual Online
For 1990-2009 cars only

Strategy Based Diagnostics

Review the system operations in order to familiarize yourself with the system functions. Refer to Rear Drive Axle Description and Operation , and Transfer Case Description and Operation . All diagnosis on a vehicle should follow a logical process. Strategy based diagnostics is a uniform approach for repairing all systems. The diagnostic flow may always be used in order to resolve a system condition. The diagnostic flow is the place to start when repairs are necessary. For a detailed explanation, refer to Strategy Based Diagnosis .

Visual/Physical Inspection

    • Inspect for aftermarket devices, which could affect the operation of the vehicle. Refer to Checking Aftermarket Accessories .
    • Inspect the easily accessible or visible system components for obvious damage or conditions, which could cause the symptom.
    • Check for the correct lubricant level and the proper viscosity.
    • Verify the exact operating conditions under which the concern exists. Note factors such as vehicle speed, road conditions, ambient temperature, and other specifics.
    • Compare the driving characteristics or sounds, if applicable, to a known good vehicle and make sure you are not trying to correct a normal condition.
    • Inspect for all-wheel drive activation and operation. Refer to All-Wheel Drive (AWD) System Functional Inspection .
    • Factors that may contribute to an inoperative rear differential include:
       - Low gear oil levels
       - Differential inoperative due to antilock brake system (ABS) function
       - Inoperative powertrain control module (PCM) and/or wiring system
       - A mini-spare or different size tire installed
       - A fluid over-temperature condition
       - An inoperative or "stuck" clutch pump check valve
       - A defective rear differential assembly
       - An inoperative transfer case assembly

Intermittent

Test the vehicle under the same conditions that the customer reported in order to verify the system is operating properly.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom:

    •  Diagnostic Starting Point - Vibration Diagnosis and Correction
    •  Diagnostic Starting Point - Wheel Drive Shafts
    •  All-Wheel Drive (AWD) System Functional Inspection
    •  Noisy in Drive
    •  Noisy When Coasting
    •  Intermittent Noise
    •  Constant Noise
    •  Noisy on Turns
    •  Rear Differential Carrier Leak Diagnosis