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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 214 (Automatic Transaxle Diagnosis - 4T65-E) >> Diagnostic Tests >> DTC P0503: Vehicle Speed Sensor Circuit Performance >> 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 DTCs, use scan tool to record freeze frame and failure records for reference. Clear DTCs. Raise and support drive wheels. Start and idle the engine. Place transaxle in Drive. Monitor OSS on the scan tool. With drive wheels rotating, increase and decrease throttle position. Does OSS RPM increase when wheel speed increases? If so, see appropriate SELF-DIAGNOSTICS article under ENGINE PERFORMANCE. If not, go to next step.
    CAUTION: 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.
  3. Turn ignition OFF. Disconnect PCM connector C1. Using Connector Test Adapter Kit (J 35616-A), connect DMM between PCM connector C1 terminals No. 64 and 65. Select AC volts on DMM. Turn ignition ON, engine OFF. Place gearshift lever in a Drive or Neutral. Rotate right front drive wheel by hand, while observing the DMM. Does the voltage measure greater than .4 volt AC? If so, go to step  8 . If not, go to next step.
  4. Leave the DMM test leads connected between PCM connector C1 terminals No. 64 and 65. Select ohms on DMM. Measure resistance of complete VSS circuit. Is circuit resistance within 1650-3180 ohms? If so, go to step  9 . If not, go to next step.
  5. Is circuit resistance greater than 3180 ohms? If so, go to step  11 . If not, go to next step.
  6. Leave DMM test leads connected between PCM connector C1 terminals No. 64 and 65. Disconnect VSS connector at transaxle. Test high signal circuit (CKT 400) and low signal circuit (CKT 401) of VSS for a short together. Are signal and ground circuits shorted together? If so, go to next step. If not, go to step  14 .
  7. Repair short between high signal circuit (CKT 400) and low signal circuit (CKT 401). Did you complete the repair? If so, go to step  16 .
  8. Test high signal circuit (CKT 400) of VSS for short to ground between PCM and VSS. Did you find and correct condition? If so, go to step  16 . If not, go to step  15 .
  9. Reconnect PCM connector C1. Select DC volts on DMM. Using connector test adapter kit, connect DMM between terminals "A" and "B" of 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 high signal circuit (CKT 400). Did you complete the repair? If so, go to step  16 .
  11. Test high signal circuit (CKT 400) of VSS for an open between PCM and VSS. Did you find and correct condition? If so, go to step  16 . If not, go to next step.
  12. Test low signal circuit (CKT 401) of the VSS for an open between the PCM and the VSS. Did you find and correct condition? If so, go to step  16 . If not, go to step  14 .
  13. Remove the VSS. See VEHICLE SPEED SENSOR under REMOVAL & INSTALLATION in SERVICING - CENTURY & REGAL article. Inspect VSS and transaxle 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.

    Repair any of the above items as necessary. Did you find and correct 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:
    • Using a scan tool, select DTC.
    • Select Clear Info.
    • Drive vehicle.
    • Ensure output shaft speed is greater than 300 RPM for at least 2 seconds.
    • Select SPECIFIC DTC.
    • Enter DTC P0503.

    Has 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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