DTC P0171: Fuel System Too Lean; DTC P0172: Fuel System Too Rich
- Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION ).
- Poor fuel quality can 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: MAF sensor
P0106, P0107, P0108: MAP sensor
P0133, P1157, P1172, P2195, P2238, P2252, P2A00: A/F sensor(Sensor 1)
P0134, P0135: A/F sensor (Sensor 1) heater
P0137, P0138, P0139: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P0522, P0523, P055B, P055C, P055D, P1286, P128A, P128C, P128D, P2646, P2648, P2649, P2653, P2654, P3400: VTEC system
P0401, P0404, P0406, P2413: EGR 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 -Check these items:
- If the pressure is too high, replace the fuel pressure regulator (see FUEL PRESSURE REGULATOR REPLACEMENT ), then go to step 2.
- If the pressure is too low, check the fuel pump, the fuel pressure regulator, the fuel filter, and the fuel line for restrictions, then go to step 6.
- Check for vacuum leaks at these parts:
- PC V valve
- PCV hose
- EVAP canister purge valve
- Throttle body
- Intake manifold
- Brake booster
- Brake booster hose
- Intake air duct
Are the parts OK?
YES -Go to step 3.
NO -Repair or replace the leaking part(s), then go to step 6.
- Start the engine. Hold the engine speed at 3,000 rpm without load (in P or N) 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)
- Transmission in P or N
- All electrical loads off
- Monitor the ENGINE SPEED in the DATA LIST with the HDS, raise and hold the engine speed steady at 2,400-2,600 rpm. While holding the rpm steady, check the MAF SENSOR in the DATA LIST.
Is there about 4.7-5.7 gm/s?
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 6.
NO -Replace the MAF sensor/IAT sensor (see MAF SENSOR/IAT SENSOR REPLACEMENT ), then go to step 6.
- Turn the ignition switch to ON (II).
- Reset the PCM with the HDS.
- Do the PCM idle learn procedure (see PCM IDLE LEARN PROCEDURE ).
- Start the engine. Hold the engine speed at 3,000 rpm without load (in P or N) 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)
- Transmission in D
- Drive at a steady speed between 15-75 mph (24-120 km/h) for 15 minutes
NOTE: 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.