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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 220 (Automatic Transaxle Diagnosis - 4T65-E) >> Diagnostic Tests >> DTC P0502: Vehicle Speed Sensor Circuit (Low Input) >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Buick Regal and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the diagnostic system check? If so, go to next step. If not, see DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Install a scan tool. Turn ignition ON, engine OFF. Before clearing the DTCs, use the scan tool to record freeze frame and failure records for reference. Clear DTCs. Raise and support the drive wheels. Start and idle the engine. Place the gearshift lever in Drive. Monitor OSS on the scan tool. With the drive wheels rotating, increase and decrease the throttle position. Does OSS RPM increase when wheel speed increases? If so, see DIAGNOSTIC AIDS  . If not, go to next step.
    CAUTION: Support the lower control arms in the normal horizontal position to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel.
  3. Turn ignition OFF. Disconnect the PCM connector C1. Using Connector Test Adapter Kit (J 35616-A), connect DMM between PCM harness connector C1 terminals No. 64 and 65. Select AC volts on DMM. Turn ignition ON, engine OFF. Place gearshift lever in Drive or Neutral. Rotate right front drive wheel by hand, while observing the DMM. Does the voltage measure greater than .4 volts AC? If so, go to step  15 . If not, go to next step.
  4. Leave the DMM connected between PCM harness connector C1 terminals No. 64 and 65. Select ohms on the DMM. Measure the resistance of complete VSS circuit. Is the circuit resistance within 1650-3180 ohms? If so, go to step  8 . If not, go to next step.
  5. Is the circuit resistance within 1650-3180 ohms? If so, go to step  11 . If not, go to next step.
  6. Leave the DMM test leads connected between PCM harness connector C1 terminals No. 64 and 65. Disconnect the VSS connector at transaxle. Test the high signal circuit (CKT 400) and the low signal circuit (CKT 401) of the VSS for a short together. Measure from PCM harness connector C1 terminals No. 64 and 65. Are the signal and ground circuits shorted together? If so, go to next step. If not, go to step  14 .
  7. Repair short between the high signal circuit (CKT 400) and the low signal circuit (CKT 401). Did you complete the repair? If so, go to step  16 .
  8. Test the high signal circuit (CKT 400) of the VSS for a short to ground between PCM and VSS. Did you find and correct the condition? If so, go to step  16 . If not, go to step  15 .
  9. Reconnect PCM connector C1. Select DC volts on the DMM. Using the connector test adapter, connect DMM between terminals "A" and "B" of the VSS vehicle harness. Turn ignition ON, engine OFF. Does DMM display greater than 1.0 volt. If so, go to next step. If not, go to step  13 .
  10. Repair short to power in the high signal circuit (CKT 400). Did you complete the repair? If so, 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 so, go to step  16 . If not, 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 so, go to step  16 . If not, go to step  14 .
  13. Remove the VSS. Inspect the VSS and the transaxle for the following:
    • Incorrect VSS or 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 so, go to step  16 . If not, go to next step.

  14. Replace the VSS. See VEHICLE SPEED SENSOR  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  16 .
  15. Replace the PCM. See POWERTRAIN CONTROL MODULE  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to next step.
  16. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select Clear Info.
    • Drive the vehicle.
    • Ensure output shaft speed is greater than 250 RPM for at least 2 seconds.
    • Select SPECIFIC DTC.
    • Enter DTC P0502.

    Has the test run and passed? If so, go to next step. If not, go to step  2 .

  17. With a scan tool, observe the stored information, capture info and DTC info. If there are any DTCs that are displayed by the scan tool and have not been diagnosed, go to the appropriate SELF-DIAGNOSTICS article under ENGINE PERFORMANCE. If there are no more codes, the system is OK.
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