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 (see 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, P1157, P1172, 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, P2271: Secondary HO2S (Sensor 2)

P0141: Secondary HO2S (Sensor 2) heater

P0443, P0496: EVAP canister purge valve

P2646, P2647, P2648, P2649: VTEC system

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:
- PCV 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 part(s) with leaks, then go to step 7.
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 P or 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 6.4- 9.2 gm/s?

YES -Check the engine valve clearances and adjust them if needed (see VALVE CLEARANCE ADJUSTMENT ). If the valve clearances are OK, replace the injectors (see INJECTOR REPLACEMENT ), then go to step 7.

NO -Replace the MAF sensor/I AT sensor (see MAF SENSOR/IAT SENSOR REPLACEMENT ), then go top 7.
Turn the ignition switch to ON (II).
Reset the ECM/PCM with the HDS.
Do the ECM/PCM idle learn procedure (see 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.
Check under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158°F (701)
- A/T in P or N, M/T in neutral
- All electrical loads off
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.
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 DTCs troubleshooting.