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.

P0101, P0102, P0103: Mass airflow (MAF) sensor ('03-04 SULEV, LX-P models and '05-07 models)
P0107, P0108, P1128, P1129: Manifold absolute pressure (MAP) sensor
P0133, P1172 ('05-07 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 ('05-07 models), P2271 ('05-07 models): Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P2646, P2647, P2648, P2649: VTEC system
P0401, P0404, P0406, P2413: Exhaust gas recirculation (EGR) system
P2279: Intake air leakage ('03-04 SULEV, LX-P models)
P0443, P0496: EVAP canister purge valve ('03-04 SULEV, LX-P models and '05-07 models)

1. Check the fuel pressure.

Is the fuel pressure OK ?

YES -
'03-04 SULEV, LX-P models and '05-07 models: Go to step 2.
'03-04 except SULEV, LX-P models: Check the engine valve clearances and adjust if necessary. If the Valve clearances are OK, replace the injectors, then go to step 7.

NO -
- If the pressure is too high, replace the fuel pressure regulator, then go to step 7.
- If the pressure is too low, check the fuel pump and the fuel feed line. Then go to step 7.

2. Check these parts for vacuum leaks:
- PCV valve
- PCV hose
- EVAP canister purge valve
- Throttle body
- Intake manifold
- Brake: booster hose

Are the parts OK?

YES - Go to step 3.

NO - Repair or replace parts with leaks, then go to step 7.

3. 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.
4. Check for these conditions:
- ECT SENSOR above 176 °F (80 °C)
- GM/T in neutral (A/T in Park or neutral)
- All electric load off

5. Monitor the ENGINE SPEED in the DATA LIST with the HDS, and hold the engine speed at 4,500 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 4,500 rpm?

YES - Repeat step 5.

NO - Go to step 6.

6. While holding the engine speed at 4,500 rpm, check the MAF SENSOR in the DATA LIST with the HDS.

Is there about 14-20 gm/s?

YES - Check the engine valve clearances and adjust if necessary. If the valve clearances are OK, replace the injectors, then go to step 7.

NO - Replace the MAF sensor/IAT sensor, then go to step 7.

7. Turn the ignition switch ON (II).
8. Reset the ECM/PCM with the HDS.
9. Do the ECM/PCM idle learn procedure. Programming and Relearning
10. 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.
11. Test-drive under these conditions:
- ECT SENSOR above 176 °F (80 °C )
- M/T in neutral (A/T in Park or neutral)
- All electric loads off

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 - 1.20, there is no problem at this time.

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

Is DTC P0171 or P0175 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.