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
P0191: Fuel Pressure Sensor
P0135: Primary Heated Oxygen Sensor (Primary HO2S) (Sensor 1) heater
P0137, P0138: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater

1. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
2. Check the primary HO2S (Sensor 1) output with a scan tool or the HDS.

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

YES - Replace the primary HO2S (Sensor 1).

NO - Go to step 3.

3. Turn the ignition switch OFF.
4. Inspect the vacuum hose routing of the fuel pressure regulator P2 for leaks, restrictions, or misrouting.

Is the hose OK?

YES - Go to step 5.

NO - Correct as necessary.

5. Turn the ignition switch ON (II), then check for fuel leakage.

Is there any fuel leakage?

YES - Check the fuel line routing of the entire fuel system.

NO - Go to step 6.

6. Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
7. Raise the engine speed to above 3,000 rpm, then check the fuel pressure sensor with the scan tool.

Is 0.05 V or more indicated?

YES - Go to step 8.

NO - Replace the fuel pressure sensor.

8. Use a scan tool to check the fuel pressure sensor with the engine idling.

Is there 2.33 - 2.93 V?

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

NO - Go to step 9.

9. Substitute a known-good fuel pressure sensor, then recheck it.

Is 0.05 V or more indicated, and/or is there 2.33 - 2.93 V?

YES - Replace the fuel pressure sensor.

NO - Replace the fuel pressure regulator P1/P2.