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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 81 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P0500: Vehicle Speed Sensor (ALLISON A/T) >> Diagnostic Procedures

Diagnostic Procedures

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  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records from the TCM.
  2. Install a scan tool. Turn ON the ignition, with the engine OFF. Using the Clear Info function erases stored DTCs in both the TCM and PCM. Record the DTC Freeze Frame and Failure Records. Is there a DTC P0721 or P0722 present? If yes, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. If no, go to next step.
    3. CAUTION: To avoid any vehicle damage, serious personal injury or death when major components are removed from the vehicle and the vehicle is supported by a hoist, support the vehicle with jack stands at the opposite end from which the components are being removed.
    NOTE: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records from the PCM.
  3. Install a scan tool. Turn ON the ignition, with the engine OFF. Using the Clear Info function erases stored DTCs in both the PCM and TCM. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Raise and support the vehicle. Start and idle the engine. Turn OFF the traction control system, if equipped. Select and monitor Engine Data 1/Vehicle Speed on the scan tool. Place the transmission into Drive. With the drive wheels rotating, slowly increase the engine speed. Does Vehicle Speed on the scan tool increase with wheel speed? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to next step.
  4. Turn OFF the engine. Disconnect connector C2 at the PCM. Turn the ignition to the ON position. Using the Digital Multimeter (DMM) and the J 35616-A GM Terminal Test Kit, test the signal circuit (CKT 400) for voltage between pin 21 and ground. Is the circuit voltage -5.0 V to 4.0 V or +5.0 V to 4.0 V? If yes, go to step  7. If no, go to next step.
  5. Turn OFF the ignition. Test the signal circuit (CKT 400) between the TCM and PCM for the following:
    • An open circuit.
    • A short to ground.

    Did you find and correct a condition? If yes, go to step  8. If no, go to next step.

  6. Replace the TCM. After repairs, go to step  8.
  7. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  8. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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