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Home › Oldsmobile › 1996 › Eighty-Eight Base › Repair and Diagnosis › Engine Performance › System › Engine Control Systems Tests W/Codes › Diagnostic Trouble Codes › DTC P1520 - Park Neutral Position Switch Circuit › Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Apply parking brake. Turn ignition on. Place gear selector in Park. Using scan tool, read PARK NEUTRAL POSITION. If scan tool displays PARK/NEUTRAL, go to next step. If scan tool does not display PARK/NEUTRAL, go to step 5).
  3. Place gear selector in Neutral. Read scan tool PARK NEUTRAL POSITION. If scan tool displays PARK-NEUTRAL, go to next step. If scan tool does not display PARK-NEUTRAL, go to step 8).
  4. Read scan tool PARK NEUTRAL POSITION while moving gear selector through Reverse and all drive gears. If scan tool displays PARK/NEUTRAL while in any Reverse or drive gear, go to step 6). If scan tool does not display as specified, see DIAGNOSTIC AIDS.
  5. Turn ignition off. Disconnect PCM connectors. Connect a test light between battery voltage and PNP input circuit at PCM. Observe test light while moving gear selector to Park and Neutral positions. If test light illuminates in Park and Neutral, go to step 10). If test light does not illuminate as specified, go to step 9).
  6. Disconnect PNP switch harness connector. Observe PNP display on scan tool. If scan tool displays PARK/NEUTRAL, go to next step. If scan tool does not display PARK/NEUTRAL, go to step 8).
  7. Turn ignition off. Disconnect PCM and PNP switch connectors. Connect a test light between battery voltage and PNP circuit. If test light illuminates, locate and repair short to ground in PNP circuit, and go to step 13). If test light does not illuminate, go to step 12).
  8. Attempt to adjust PNP switch. Read scan tool PARK/NEUTRAL POSITION with Park and Neutral selected. If scan tool displays PARK/NEUTRAL, go to step 13). If scan tool does not display PARK/NEUTRAL, go to step 11).
  9. Check for open PNP input circuit, open ground circuit to PNP switch, or faulty connection at PNP switch. If a problem is found, repair as necessary and go to step 13). If no problem is found, go to step 11).
  10. Check for faulty PNP input circuit connection at PCM. If faulty connection is found, repair as necessary and go to step 13). If connection is okay, go to step 12).
  11. Replace PNP switch and go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
  13. Clear DTCs. Observe scan tool display while placing gear selector in each gear position. If scan tool indicates correct park/neutral status in each gear position, repair is complete. If scan tool does not indicate correct status, return to step 2).
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