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Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 Chevrolet Suburban, and 2002 Chevrolet Silverado. 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 DTC, use the scan tool to record the freeze frame and failure records for reference. The CLEAR INFO function will erase the data. Record the DTC freeze frame and failure records. Clear the DTC. Raise and support the drive axle assembly. Start the engine. Place the transmission in any drive range. With the drive wheels rotating, does the output shaft speed increase with the drive wheel speed? If so, see DIAGNOSTIC AIDS . If not, go to next step.
  3. Turn ignition off. Disconnect the PCM connector C2. Using a DVOM and the Connector Test Adapter Kit (J-35616-A), measure the resistance between PCM harness connector C2 terminals No. 20 and 21. Does the resistance measure 1377-3355 ohms? If so, go to next step. If not, go to step  7.
  4. Place the transmission in Neutral. Select AC volts on DVOM. 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 volt? If so, go to next step. If not, go to step  12.
  5. Measure the resistance from PCM harness connector C2 terminal No. 21 to ground. Does the resistance measure greater than 50 k/ohms? If so, go to next step. If not, go to step  9.
  6. Reconnect the PCM connector C2. Disconnect the engine wiring harness from the OSS assembly. Turn ignition on, engine off. Test the high circuit (821) of the OSS assembly for a short to power. Did you find and correct the condition? If so, go to step  15. If not, go to step  14.
  7. Disconnect the engine wiring harness from the OSS assembly. Measure the resistance of the OSS assembly. Does the resistance measure 1377-3355 ohms? If so, go to next step. If not, go to step  13.
  8. Was the resistance measured in step  3 greater than 3355 ohms? If so, go to step  10. If not, go to step  11.
  9. Test the high circuit (821) of the OSS for a short to ground. Did you find and correct the condition? If so, go to step  15.
  10. Test the high circuit (821) of the OSS for an open. Test the low circuit (822) of the OSS for an open. Did you find and correct the condition? If so, go to step  15.
  11. Test the high circuit (821) and the low circuit (822) of the OSS for a short together. Did you find and correct the condition? If so, go to step  15.
  12. Remove the OSS assembly. Inspect the output shaft speed sensor rotor for damage or misalignment. Inspect the case extension bushing for wear. Did you find and correct the condition? If so, go to step  15. If not, go to next step.
    13. NOTE: For vehicles equipped with an active transfer case, identify the OSS assembly before replacing. There are 2 transfer case speed sensors located near the OSS assembly.
  13. Replace the OSS assembly. See SPEED SENSORS  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  15.
  14. Replace the PCM. See POWERTRAIN CONTROL MODULE  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to next step.
  15. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Ensure transmission output speed is greater than 250 RPM for 2 seconds.
    • Select SPECIFIC DTC.
    • Enter DTC P0502.

    Has the test run and passed? If so, system is okay. If not, go to step  1.

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