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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> External Pages >> Different car >> Section 338 (Transfer Case - Mp 3023/3024-NQH) >> Diagnostic Information and Procedures >> DTC C0374 >> Circuit/System Testing

Circuit/System Testing

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  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. Mechanical binding. - 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.
  7. 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, verify that the front and rear wheel speeds sensors display do not vary or become intermittent.
    • If while driving at a steady speed the RPM values vary or becomes intermittent, check the EBCM for wheel speed DTC's. Wheel speed DTC's diagnostics are in antilock brake systems.
  8. 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.
  9. 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 tear down and inspection will be required.
  10. 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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