Engine Control System

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.

P0106, P0107, P0108, P1128, P1129: MAP Sensor
P0135: Primary HO(2)S (Sensor 1) Heater
P0137, P0138: Secondary HO(2)S (Sensor 2)
P0141: Secondary HO(2)S (Sensor 2) Heater
P0401: EGR Flow Insufficient
P1259: VTEC System (F23A1, F23A4 engine)
P1491: EGR Valve Lift Insufficient
P1498: EGR Valve Lift Sensor High Voltage

1. Check the fuel pressure.

Is fuel pressure OK?

YES - Go to step 2.

NO - Check these items:

- If the pressure is too high. Check the fuel pressure regulator and the fuel return line.
- If the pressure is too low. Check the fuel pump, the fuel feed line, the fuel filter, and the fuel pressure regulator.

2. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
3. Check the Primary HO(2)S or Air Fuel Ratio (A/F) Sensor (Sensor 1) output with the scan tool.

Does it stay at less than 0.3 V or more than 0.6 V ?

YES - Replace the Primary HO(2)S or Air Fuel Ratio (A/F) Sensor (Sensor 1).

NO - Go to step 4.

4. With a vacuum pump, apply vacuum to the EVAP canister purge valve from the intake manifold side. Does it hold vacuum?

YES - Check the valve clearances and adjust if necessary. If the valve clearances are OK, replace the injectors.

NO - Replace the EVAP canister purge valve.