LEMON Manuals: Even more car manuals for everyone
Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 81 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P0503: Vehicle Speed Sensor Erratic (4L80-E A/T) >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 GMC Savana Special, 2002 GMC Savana Camper Special, and 2002 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.
  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 for reference. The Clear Info function will erase the data.
  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 rear axle assembly. Start the engine. Place the transmission in any drive range. With the drive wheels rotating, does the scan tool Transmission OSS increase with the drive wheel speed? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. Turn OFF the ignition. Disconnect the PCM connector C2. Using the J 39200 Digital Multimeter (DMM) and the J 35616-A connector test adapter kit, measure the resistance between harness connector terminal C2-20 and C2-21. Does the resistance measure 1377-3355 ohms? If yes, go to next step. If no, go to step  7.
  4. Place the transmission in Neutral. Select AC volts. Prevent one rear wheel from turning. Rotate the other rear wheel by hand, ensuring that the driveshaft is turning. Does the voltage measure greater than 0.5 V? If yes, go to next step. If no, go to step  12.
  5. Measure the resistance from terminal C2-21 to ground. Does the resistance measure greater than 50 K ohms? If yes, go to next step. If no, go to step  9.
  6. Reconnect the PCM connector C2. Disconnect the engine wiring harness from the OSS assembly. Turn ON the ignition, with the engine OFF. Test the high signal circuit (CKT 821) of the AT OSS assembly for a short to power. Did you find and correct the condition? If yes, go to step  15. If no, go to step  14.
  7. Disconnect the engine wiring harness from the OSS assembly. Measure the resistance of the AT OSS assembly. Does the resistance measure 1377-3355 ohms? If yes, go to next step. If no, go to step  13.
  8. Was the resistance measured in step  3 greater than 3355 ohms? If yes, go to step  10. If no, go to step  11.
  9. Test the high signal circuit (CKT 821) of the AT OSS assembly for a short to ground. Repair as necessary. After repairs, go to step  15.
  10. Test the high signal circuit (CKT 821) of the AT OSS assembly for an open. Test the low signal circuit (CKT 822) of the AT OSS assembly for an open. Repair as necessary. After repairs, go to step  15.
  11. Test the high signal circuit (CKT 821) and the low signal circuit (CKT 822) of the AT OSS assembly for a short together. Repair as necessary. After repairs, go to step  15.
  12. Remove the AT OSS assembly. Inspect the output shaft rotor teeth for damage or misalignment. Inspect the case extension bushing for wear. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
    13. NOTE: For vehicles equipped with an active transfer case, identify the AT OSS assembly before replacing. There are two transfer case speed sensors located near the AT OSS assembly. Refer to the wire colors on the schematic to identify the AT OSS assembly.
  13. Replace the AT OSS assembly. After repairs, go to step  15.
  14. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  15. Perform the following procedure in order to verify the repair:
    • Select DTC.
    • Select Clear Info.
    • Operate the vehicle under the following conditions:
      1. The transmission output speed is greater than 250 RPM.
      2. No RPM change greater than 300 RPM.
      3. All conditions are met for 2 seconds.
    • Select Specific DTC.
    • Enter DTC P0503.

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

scientia non olet · About LEMON Manuals