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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 123 (Engine Controls - Self-Diagnostics - 4.0L) >> Diagnostic Tests >> DTC P0503: Vehicle Speed Sensor Circuit Intermittent >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. WARNING: Support the lower control arms in the normal horizontal position in order to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel.
    NOTE: Before clearing the DTC, use the scan tool to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM.
  2. Install a scan tool. Turn the ignition ON, with the engine OFF. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Raise and support the drive wheels. Start and idle the engine. Place the transmission in DRIVE. Select Transmission OSS on the scan tool. With the drive wheels rotating, does the Transmission OSS RPM increase when the wheel speed increases? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to next step.
  3. Turn OFF the ignition. Disconnect the PCM connector C1. Using the DMM and the GM Terminal Test Kit (J 35616-A), measure the resistance between PCM terminals C1-56 and C1-57. Is the resistance 1300-1950 ohms? If yes, go to step  6. If no, go to next step.
  4. Is the resistance greater than 1950 ohms? If yes, go to step  12. If no, go to next step.
  5. Leave the DMM test leads connected. Disconnect the VSS connector at the transmission. Is the resistance less than 1300 ohms? If yes, go to step  8. If no, go to step  14.
  6. Connect the DMM between PCM terminal C1-56 and ground. Is the resistance less than 100 ohms? If yes, go to step  9. If no, go to next step.
    7. NOTE: Place the gear select lever in the Neutral position before rotating the drive wheel.
  7. Connect the DMM between PCM terminals C1-56 and C1-57. Select AC volts on the DMM. Rotate the right front drive wheel by hand. Observe the DMM display. Can a voltage greater than 0.5 V AC be obtained? If yes, go to step  10. If no, go to step  13.
  8. Repair the high signal circuit (CKT 400) and the low signal circuit (CKT 401) of the VSS for being shorted together. After repairs, go to step  16.
  9. Repair the high signal circuit (CKT 400) of the VSS for a short to ground. After repairs, go to step  16.
  10. Reconnect PCM connector C1. Using the J 35616-A, connect the DMM test leads to terminals "A" and "B" of the VSS wiring harness connector end. Select DC volts on the DMM. Turn the ignition ON, with the engine OFF. Does the DMM display system voltage? If yes, go to next step. If no, go to step  15.
  11. Repair the high signal circuit (CKT 400) of the VSS for a short to voltage. Repair any of the above conditions as necessary. After repairs, go to step  16.
  12. Test the high signal circuit (CKT 400) of the VSS for an open. Test the low signal circuit (CKT 401) of the VSS for an open. Did you find and correct a condition? If yes, go to step  16. If no, go to step  14.
  13. Remove the VSS. Inspect the VSS and the transmission for the following conditions:
    • Incorrect VSS.
    • VSS damage.
    • Excessive VSS to speed sensor rotor gap.
    • Incorrect speed sensor rotor alignment.
    • Speed sensor rotor damage.

    Repair any conditions as necessary. After repairs, go to step  16.

  14. Replace the VSS. After repairs, go to step  16.
  15. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  16. To verify the repair, select DTC. Select Clear Info. Road test the vehicle and ensure that the Transmission OSS is greater than 1198 RPM and does not drop 175 RPM or greater for 2 seconds. Select Specific DTC. Enter DTC P0503. Has the test run and passed? If yes, system is okay. If no, go to step  1.
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