DTC P0171: Fuel Trim System Lean Or DTC P0172: Fuel Trim System Rich
- Check fuel pressure. See BASIC TESTING article. If fuel pressure is within specifications, go to next step. If fuel pressure is not as specified, repair as necessary and retest system.
- Check fuel injectors. See CIRCUIT TESTS in BASIC TESTING article. If problem is present, repair as necessary and retest system. If fuel injectors are okay, go to next step.
- Check fuel lever sensor. See DTC P0461 : FUEL LEVEL SENSOR CIRCUIT PERFORMANCE. If problem is present, repair as necessary and retest system. If fuel level sensor is okay, go to next step.
- Check MAF sensor circuit performance. See DTC P0101 : MASS AIRFLOW (MAF) CIRCUIT PERFORMANCE PROBLEM. If problem is present, repair as necessary and retest system. If MAF sensor circuit is okay, go to next step.
- Check ECT sensor circuit performance. See DTC P0125 : EXCESSIVE TIME TO ENTER CLOSED LOOP. If problem is present, repair as necessary and retest system. If ECT sensor circuit is okay, go to next step.
- Check HO2S No. 1 sensor circuit performance. See DTC P0131 : HEATED OXYGEN SENSOR (HO2S) NO. 1 CIRCUIT VOLTAGE LOW and see DTC P0132 : HEATED OXYGEN SENSOR (HO2S) NO. 1 CIRCUIT VOLTAGE HIGH. If problem is present, repair as necessary. If HO2S No. 1 sensor circuit is okay, replace PCM and retest system.