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
P0135: Primary Heated Oxygen Sensor (Primary HO(2)S) (Sensor 1) heater
P0137, P0138: Secondary Heated Oxygen Sensor (Secondary HO(2)S) (Sensor 2)
P0141: Secondary Heated Oxygen Sensor (Secondary HO(2)S) (Sensor 2) heater
P0401, P1491, P1498: Exhaust Gas Recirculation (EGR) system
P1259: VTEC System

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, 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 (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 (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.