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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 ON the ignition, with the engine OFF. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Select IMS on the scan tool. Place the gearshift lever in D4. Does the scan tool IMS parameter indicate Drive 4? If so, see INTERMITTENT CONDITIONS within appropriate ENGINE PERFORMANCE article. If not, go to next step.
    NOTE: Before clearing the DTC, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the PCM.
  3. Turn OFF the ignition. Disconnect the AT inline 20-pin connector. Additional DTCs may set. Turn ON the ignition, with the engine OFF. Select IMS A/B/C/P on the scan tool. Does IMS signal A indicate LOW? If so, go to next step. If not, go to step  5 .
  4. Test the signal "A" circuit (CKT 771) of the IMS for a short to ground between the PCM connector C2 and the AT inline 20-pin connector. Did you find and correct the condition? If so, go to step  9 . If not, go to step  8 .
  5. Turn OFF the ignition. Reconnect the AT inline 20-pin connector. Disconnect the automatic transmission wiring harness at the IMS. Turn ON the ignition, with the engine OFF. Select IMS A/B/C/P on the scan tool. Does IMS signal "A" indicate LOW? If so, go to next step. If not, go to step  7 .
  6. Replace the automatic transmission wiring harness. See TRANSAXLE INTERNAL WIRING HARNESS  under REMOVAL & INSTALLATION. When replacement is complete, go to step  9 .
  7. Replace the lever assembly-manual shaft detent with internal mode switch. See PARKING SYSTEM COMPONENTS  under REMOVAL & INSTALLATION. When replacement is complete, go to step  9 .
  8. Replace the PCM. See POWERTRAIN CONTROL MODULE  under REMOVAL & INSTALLATION. When replacement is complete, go to next step.
  9. Perform the following procedure in order to verify the repair:
    • Select DTC.
    • Select Clear Info.
    • Start and idle the engine in Park for 10 seconds.
    • Select IMS A/B/C/P on the scan tool.
    • Move the gearshift lever from Park to D4.
    • Ensure that IMS signal "A" changes from LOW to HI.
    • Select Specific DTC.
    • Enter DTC P1820.

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

  10. With a scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? If so, go to appropriate ENGINE PERFORMANCE article. If not, the system is OK.
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