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Circuit/System Testing

WARNING: This page is about a different car, the 2012 GMC Yukon XL, 2012 GMC Yukon, 2012 Chevrolet Tahoe, and 2012 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
  1. Install scan tool.
  2. Wheel speed sensors - Take the vehicle on a short test drive on a smooth and level road. Using the Data Display function of the ECBM feature of the scan tool, when at a steady speed verify that the front and rear wheel speeds sensor displays do not vary or become intermittent.
    • If while driving at a steady speed the RPM values vary or become intermittent, check the EBCM for wheel speed DTC's. Wheel speed DTC diagnostics are in antilock brake systems.
  3. Transfer case clutch integrity - Shift the vehicle into 4WD HI and take it for a test drive. Clear the DTC if possible. Monitor front and rear wheel speeds using the EBCM data display. Under heavy acceleration the front and rear wheel speeds should be similar.
    • If the front wheel speeds are much lower, this indicates a weak clutch and a transfer case disassembly and inspection will be required. Refer to Transfer Case Disassemble .
  4. Transfer case encoder motor brake - Using a scan tool clear DTC's. Shift the vehicle to 2WD HI. Monitor the Transfer Case Motor Amperage parameter in the Data Display feature of the scan tool. Using the transfer case shift control switch, command the transfer case to the 4WD HI mode. The transfer case motor amperage should increase while the motor is shifting, and then return to 0 amps within 5 seconds or less.
    • If the amperage stays high longer than 5 seconds, this indicates the brake is not holding. Replace the transfer case motor.
  5. Mechanical binding -
    1. Engage parking brake.
    2. Block rear wheels.
    3. Lift front wheels.
    4. Key ON, engine OFF. Install scan tool.
    5. Transfer case in 2WD HI. Transmission in Neutral.
    6. Using the Special Functions capability of the scan tool, engage the front axle. While holding one front tire stationary, spin the other tire. The front propshaft should turn.
      • If the front propshaft does not turn, inspect the front axle clutch fork for mechanical binding.
  6. If all prior evaluations test normal, reprogram the TCCM and perform the ATC Motor Learn procedure in the Special Functions feature of the scan tool or the Transfer Case High/Low Clutch Reset  procedure in the service manual.
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