DTC P0171: Fuel System Too Lean; DTC P0172: Fuel System Too Rich

NOTE:

If some of the DTCs listed below are stored at the same time as DTC P0171 and/or P0172, troubleshoot those DTCs first, then recheck for P0171 and/or P0172.
Before you troubleshoot, record all freeze data and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION ).

P0107, P0108, P1128, P1129: Manifold absolute pressure (MAP) sensor

P0135: Primary heated oxygen sensor (primary HO2S) (Sensor 1) heater

P0137, P0138: Secondary HO2S (Sensor 2)

P0141: Secondary HO2S (Sensor 2) heater

P1259 (P2646, P2647)*: VTEC system

*: 2004-2005 models

Check the fuel pressure (see FUEL PRESSURE RELIEVING ).
Is fuel pressure OK?
1. YES - Go to step 2.
2. NO - Check these items:
  - If the pressure is too high. Check the fuel pressure regulator, and the fuel return pipe.
  - If the pressure is too low. Check the fuel pump, the fuel feed pipe, the fuel filter, and the fuel pressure regulator.
Start the engine. Hold the engine speed at 3,000 RPM without load (in neutral) until the radiator fan comes on.
Check the primary HO2S (Sensor 1) output with a scan tool or the HDS.
Does it stay less than 0.3 V or more than 0.6 V?
1. YES - Replace the primary HO2S (Sensor 1) (see PRIMARY HO2S REPLACEMENT ).
2. NO - Go to step 4.
Turn the ignition switch OFF.
With a vacuum pump, apply vacuum to the EVAP canister purge valve from the intake manifold side.
Does it hold vacuum?
1. YES - Check the valve clearances and adjust if necessary. If the valve clearances are OK, replace the injectors.
2. NO - Replace the EVAP canister purge valve.