LEMON Manuals: Even more car manuals for everyone
Home >> Buick >> 2003 >> Regal LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0502: Vehicle Speed Sensor Circuit - Low Output >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing Diagnostic System Check - Engine Controls, go to next step.
    2. NOTE: Support lower control arms in normal horizontal position to avoid damage to drive axles. Do not operate vehicle in gear with wheels hanging down at full travel.
  2. Install a scan tool. Turn ignition on, engine off. Record FREEZE FRAME/FAILURE RECORDS. Clear DTCs. Raise and support drive wheels. Start and idle engine. Place transmission in Drive. Monitor transmission VSS on scan tool. With drive wheels rotating, increase and decrease throttle position. Does the Transmission VSS 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 Connector Test Adapter Kit (J 35616-A), connect the DVOM between terminals C1-64 and C1-65 of the PCM harness connector. Select AC volts on the DVOM. Turn ignition on, with engine off. Place the range selector in a Drive range or Neutral. Rotate the right front drive wheel by hand, while observing the DVOM display. Does the voltage measure greater than 0.4 volt AC? If yes, go to step  8. If no, go to next step.
  4. Leave the DVOM test leads connected between terminals C1-64 and C1-65 of the PCM harness connector. Select ohms on the DVOM. 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 resistance more than 3180 ohms? If yes, go to step  11. If no, go to next step.
  6. Leave the DVOM test leads connected between terminals C1-64 and C1-65 of the PCM harness connector. 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. Measure from PCM connector terminal C1-64 to C1-65. 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 PCM connector C1. Select DC volts on DVOM. Connect DVOM between terminals "A" and "B" of the VSS vehicle harness. Turn ignition on, with engine off. Does the DVOM display greater than one volt? 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 VSS. Inspect VSS and transmission for the following:
    • Incorrect VSS.
    • VSS damage.
    • Excessive runout in final drive carrier assembly.
    • Excessive VSS to speed sensor rotor gap.
    • Incorrect speed sensor rotor alignment.
    • Speed sensor rotor damage.

    If problem was found, repair as necessary. See appropriate OVERHAUL article in AUTOMATIC TRANSMISSIONS. Did you find and correct the condition? If yes, go to step  16. If no, go to next step.

  14. Replace VSS. After repairs, go to step  16.
  15. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  16. To verify repair, select DTC. Select CLEAR INFO. Drive vehicle. Ensure transmission VSS is more than 250 RPM for at least 2 seconds. Select SPECIFIC DTC. Enter DTC P0502. If test has run and passed, system is okay. If test did not rum and pass, go to step  2.
scientia non olet · About LEMON Manuals