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DTC P1391 - "G" Sensor Circuit Performance

  1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P1391. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1391 FAILED THIS IGN, go to step 4). If scan tool does not display DTC P1391 FAILED THIS IGN, go to next step.
  3. Check for "G" sensor seal missing, damaged or mounting flanges cracked, missing or incorrectly installed. If problem is found, repair as necessary. Retest system. If no problem is found, check for an intermittent problem. See TESTS W/O CODES article.
  4. Disconnect "G" sensor electrical connector. Using scan tool, observe "G" sensor value. If value is about zero volts, go to next step. If value is not as specified, go to step 12).
  5. Connect jumper wire between "G" sensor reference and signal circuit at harness connector. Using scan tool, read "G" sensor value. If "G" sensor value is about 4.95 volts, go to next step. If value is not as specified, go to step 7).
  6. Turn ignition off. Disconnect PCM connector. Check sensor ground circuit for high resistance, poor connection at PCM or an open between PCM and "G" sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 10).
  7. Check 5-volt reference circuit for high resistance, open between PCM and "G" sensor or a poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  8. Check signal circuit for high resistance, open, short to ground or short to sensor ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  9. Check "G" sensor circuit for poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 13).
  10. Check for poor connection at "G" sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  11. Replace "G" sensor. Retest system.
  12. With ignition off, disconnect PCM. Turn ignition on. Check "G" sensor signal circuit for a short to voltage or short to 5-volt reference circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  13. Replace PCM. Retest system.
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