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Home >> Pontiac >> 2002 >> Aztek FWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0502: Vehicle Speed Sensor Low Output >> Diagnostic Procedures
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Diagnostic Procedures

  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. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM.
    CAUTION: 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.
  2. Install a scan tool. Turn ON the ignition, 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. Monitor Transmission OSS on the scan tool. With the drive wheels rotating, increase and decrease the throttle position. Does the Transmission OSS RPM increase when 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 J 35616-A connector test adapter kit, connect the J 39200 Digital Multimeter (DMM) between PCM harness connector terminals C1-64 and C1-65. Select AC volts on the J 39200 DMM. Turn ON the ignition with the engine OFF. Place the range selector in a Drive range or Neutral. Rotate the right front drive wheel by hand, while observing the J 39200 DMM display. Does the voltage measure greater than 0.4 V AC? If yes, go to step  8. If no, go to next step.
  4. Leave the J 39200 DMM test leads connected between PCM connector terminals C1-64 and C1-65. Select ohms on the J 39200 DMM. Measure the resistance of the complete VSS circuit. Is the circuit resistance 1650-3180 ohms? If yes, go to step  9. If no, go to next step.
  5. Is the circuit resistance greater than 3180 ohms? If yes, go to step  11. If no, go to next step.
  6. Leave the J 39200 DMM test leads connected between PCM connector terminals C1-64 and C1-65. Disconnect the VSS connector at the transmission. Test the high signal circuit (CKT 400) and the low signal circuit (CKT 401) of the VSS for a short together. Are the signal and ground circuits shorted together? If yes, go to next step. If no, go to step  14.
  7. Repair the short between the high signal circuit (CKT 400) and the low signal circuit (CKT 401). After repairs, go to step  16.
  8. Test the high signal circuit (CKT 400) of the VSS for a short to ground between the PCM and the VSS. Did you find and correct the condition? If yes, go to step  16. If no, go to step  15.
  9. Reconnect the PCM connector C1. Select DC volts on the J 39200 DMM. Using the J 35616-A connector test adapter kit, connect the J 39200 DMM between terminals "A" and "B" of the VSS vehicle harness. Turn ON the ignition with the engine OFF. Does the J 39200 DMM display greater than 1.0 V? If yes, go to next step. If no, go to step  13.
  10. Repair the short to power in the high signal circuit (CKT 400). After repairs, go to step  16.
  11. Test the high signal circuit (CKT 400) of the VSS for an open between the PCM and the VSS. Did you find and correct the condition? If yes, go to step  16. If no, go to next step.
  12. Test the low signal circuit (CKT 401) of the VSS for an open between the PCM and the VSS. Did you find and correct the condition? If yes, go to step  16. If no, go to step  14.
  13. Remove the VSS assembly. See appropriate TRANSMISSION SERVICING article in AUTOMATIC TRANSMISSION. Inspect the VSS and the transmission for the following:
    • Incorrect VSS.
    • VSS damage.
    • Excessive runout in the final drive carrier assembly.
    • Excessive VSS to speed sensor rotor gap.
    • Incorrect speed sensor rotor alignment.
    • Speed sensor rotor damage.

    Repair any of the above items as necessary. Did you find and correct the condition? If yes, go to step  16. If no, go to next step.

  14. Replace the VSS assembly. 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. Perform the following procedure in order to verify the repair:
    • Select DTC.
    • Select Clear Info.
    • Drive the vehicle.
    • Operate the vehicle, so that the transmission output speed is greater than 250 RPM for 2 seconds.
    • Select Specific DTC.
    • Enter DTC P0502.

    Has the test run and passed? If yes, system is okay. If no, go to step  1.

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