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Home >> Cadillac >> 2003 >> Seville SLS >> 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. 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.
    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.
  2. Install a scan tool. Turn ignition on, with 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, 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 ignition off. Disconnect the PCM connector C1. Using the Connector Test Adapter Kit, connect the DVOM between PCM harness connector terminals C1-56 and C1-57. Select AC volts. Place transmission in NEUTRAL. Rotate the right front drive wheel by hand. Does the voltage measure greater than 0.5 volts AC? If yes, go to step  14. If no, go to next step.
  4. Leave the DVOM test leads connected. Measure circuit resistance. Is the circuit resistance 1300-1950 ohms? If yes, go to step  8. If no, go to next step.
  5. Is the circuit resistance greater than 1950 ohms? If yes, go to step  11. If no, go to next step.
  6. Leave the DVOM test leads connected. Disconnect the VSS connector at the transmission. Is the circuit resistance less than 1300 ohms? If yes, go to next step. If no, go to step  13.
  7. Repair the short between the VSS high signal circuit (CKT 400) and the VSS low signal circuit (CKT 401). Did you find and correct the condition? If yes, go to step  15.
  8. Test the VSS high signal circuit (CKT 400) for a short to ground. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  9. Reconnect the PCM connector C1. Select DC volts on the DVOM. Using the Connector Test Adapter Kit, connect the DVOM between terminals "A" and "B" of the VSS vehicle harness. Turn ignition on, with engine off. Does the DVOM display system voltage? If yes, go to next step. If no, go to step  12.
  10. Test the VSS high signal circuit (CKT 400) for a short to voltage. Did you find and correct the condition? If yes, go to step  15.
  11. Test the VSS high signal circuit (CKT 400) for an open. Test the VSS low signal circuit (CKT 401) for an open. Did you find and correct the condition? If yes, go to step  15. If no, go to step  13.
  12. Remove the VSS assembly. See VEHICLE SPEED SENSOR under REMOVAL & INSTALLATION in SERVICING - DEVILLE & SEVILLE article in AUTOMATIC TRANSMISSIONS. Inspect the VSS and the transmission for the following:
    • Incorrect VSS.
    • VSS damage.
    • 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  15.

  13. Replace the VSS assembly. See VEHICLE SPEED SENSOR under REMOVAL & INSTALLATION in SERVICING - DEVILLE & SEVILLE article in AUTOMATIC TRANSMISSIONS. Did you complete the replacement? If yes, go to step  15.
  14. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to next step.
  15. Perform the following procedure in order to verify the repair:
    • Select DTC.
    • Select Clear Info.
    • Operate the vehicle in order to achieve a Transmission OSS of greater than 1855 RPM for 2 seconds.
    • Select Specific DTC.
    • Enter DTC P0502.

    Has the test run and passed? If yes, go to step. If no, go to step. 2.

  16. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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