DTC P0171, P0172: Fuel System Too Lean; Fuel System Too Rich
- Before you troubleshoot, record all freeze data and any on-board snapshot, and review GENERAL TROUBLESHOOTING INFORMATION .
- Poor fuel quality can also cause DTC P0171.
- If any of the DTCs listed below are indicated at the same time as DTC P0171 and/or P0172, troubleshoot those DTCs first, then recheck for P0171 and/or P0172.
P0101, P0102, P0103: Mass air flow (MAF) sensor
P0107, P0108, P1128, P1129: Manifold absolute pressure (MAP) sensor
P0133, P1172, P1157, P2195, P2238, P2252, P2A00: Air fuel ratio (A/F) sensor (Sensor 1)
P0134, P0135: Air fuel ratio (A/F) sensor (Sensor 1) heater
P0137, P0138, P0139: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P2646, P2647, P2648, P2649: VTEC system
P0443, P0496: EVAP canister purge valve
- Check the fuel pressure (see FUEL PRESSURE TEST
).
Is the fuel pressure OK?
YES: Go to step 2.
NO:
- If the pressure is too high, replace the fuel pressure regulator (see FUEL PRESSURE REGULATOR REPLACEMENT ), then go to step 7.
- If the pressure is too low, check the fuel pump, the fuel feed pipe, and the fuel filter. If they are OK, replace the fuel pressure regulator (see FUEL PRESSURE REGULATOR REPLACEMENT ), then go to step 7.
- Check for vacuum leaks at these parts:
- Start the engine. Hold the engine speed at 3, 000 rpm without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle.
- Check under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158°F (70°C)
- A/T in N, M/T in neutral
- All electrical loads off
- Monitor the ENGINE SPEED in the DATA LIST with the HDS, and hold the engine speed at 2, 500 rpm. Once the engine speed is met, hold the accelerator pedal steady for more than 10 seconds.
Did the engine speed vary more than 100 rpm from 2, 500 rpm?
YES: Repeat step 5.
NO: Go to step 6.
- While holding the engine speed at 2, 500 rpm, check the MAF SENSOR in the DATA LIST with the HDS.
Is there about 4.6-5.7 gm/s (M/T) or 4.7-5.7 gm/s (A/T)?
YES: For DTC P0172, check the engine valve clearances, and adjust them if needed (see VALVE CLEARANCE ADJUSTMENT ). For DTC P0171, replace the injectors (see INJECTOR REPLACEMENT ), then go to step 7.
NO: Replace the MAF sensor/IAT sensor (see MAF SENSOR/IAT SENSOR REPLACEMENT ), then go to step 7.
- Turn the ignition switch to ON (II).
- Reset the ECM/PCM with the HDS.
- Do ECM/PCM IDLE LEARN PROCEDURE .
- Start the engine. Hold the engine speed at 3, 000 rpm without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle.
- Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158°F (70°C)
- A/T in D, M/T in 3rd or 4th
- Drive at a steady speed between 15-75 mph (24-120 km/h) for 15 minutesNOTE: DTC P0171 and/or P0172 may take up to 80 minutes of test driving to set. Using the HDS, monitor the long term fuel trim (LT FUEL TRIM) or the air fuel feed back average (AF FB AVE). If the long term fuel trim/air fuel feed back average stays within 0.80-1.25, there is no problem at this time.
- Check for Pending or Confirmed DTCs with the HDS.
Is DTC P0171 or P0172 indicated?
YES: Go to step 1.
NO: Troubleshooting is complete. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting.