DTC Troubleshooting

DTC P0171: Fuel System Too Lean

DTC P0172: Fuel System Too Rich

NOTE:
- Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information.
- If some 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.

P0107, P0108, P1128, P1129: Manifold absolute pressure (MAP) sensor
P0133, P1172 ('05-08 models), 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, P2270 ('05-08 models), P2271 ('05-08 models): Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P2279: Intake air leakage
P2646, P2647, P2648, P2649: VTEC system

1. Check the fuel pressure.

Is the fuel pressure OK?

YES - Check the engine valve clearances and adjust if necessary (P0172 only). If the valve clearances are OK, replace the injectors, then go to step 2.

NO
- If the pressure is too high, replace the fuel pressure regulator, then go to step 2.
- If the pressure is too low, check the fuel pump and the fuel feed line, then go to step 2.

2. Turn the ignition switch ON (II).
3. Reset the ECM/PCM with the HDS.
4. Do the ECM/PCM idle learn procedure.
5. Start the engine. Hold the engine speed at 3,000 rpm without load (in Park or neutral) until the radiator fan comes on, then let it idle.

6. Test-drive under these conditions:

- Engine coolant temperature (ECT SENSOR) ('04-05 models). Engine coolant temperature (ECT SENSOR 1) ('06-08 models) above 158 °F (70 °C)
- A/T in D position (M/T in 4th gear)
- Drive at a steady speed between 15-75 mph (24-120 km/h)

NOTE: DTC P0171 and/or P0172 may take up to 80 minutes of test driving to set. Using the HDS, monitor the air fuel feed back average (AF FB AVE). If the AF FB AVE stays within 0.80-1.25, there is no problem at this time.

7. Check for Temporary DTCs or DTCs with the HDS.

Is DTC P0171 or P0172 indicated?

YES - Go to step 1.

NO - Troubleshooting is complete. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.