P0172

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.

P0107, P0108, P1128, P1129: Manifold absolute pressure (MAP) sensor
P1161, P1167: A/F sensor (Sensor 1) heater
P0137, P0138: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P0340,P0344: CMP sensor A
P1259: VTEC system

1. Monitor short term fuel trim (AF FB) at steady cruise, and at idle.

Is the AF FB above 1.10 (P0171) or below .90 (P0172)?

YES - Go to step 2.

NO - Intermittent failure, system is OK at this time.

2. Check the fuel pressure.

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.
- If the pressure is too low, check the fuel pump, the fuel feed line, and the fuel filter, and replace the fuel pressure regulator.

3. Turn the ignition switch OFF.




4. With a vacuum pump, apply vacuum to the evaporative emission (EVAP) canister purge valve (A) from the evaporative emission (EVAP) canister side.

Does the valve hold vacuum?

YES -

- P0171: Replace the fuel injectors.
- P0172: Check the engine valve clearances, and adjust them if needed. If the valve clearances are OK, replace the fuel injectors.

NO - Replace the EVAP canister purge valve.