DTC P0171: Fuel Trim System Lean Or DTC P0172: Fuel Trim System Rich

Check diagnostic system to determine if any other diagnostic tests codes (DTCs) are present. If other DTCs are present, go to appropriate test procedure first. See DIAGNOSTIC TESTS . If no other DTCs are indicated, go to next step.
Inspect intake and exhaust systems for leaks. If any leaks are detected, repair them and retest system. If intake and exhaust systems are okay, go to next step.
Check fuel pressure. See CIRCUIT TEST B-3: FUEL PRESSURE INSPECTION under CIRCUIT TESTS in BASIC DIAGNOSTIC PROCEDURES 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 TEST B-1: FUEL INJECTOR CIRCUIT INSPECTION under CIRCUIT TESTS in BASIC DIAGNOSTIC PROCEDURES 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 OR 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.