DTC P0172: Fuel System Too Rich

Special Tools Required

Vacuum Pump/Gauge, 0-30 inHg Snap-on YA4000A or equivalent, commercially available

NOTE:

Before you troubleshoot, review the general troubleshooting information - Refer to: How to Troubleshoot the Fuel and Emissions Systems How to Troubleshoot the CVT System(CVT System) .
Do not clear the DTC or reset the PCM before beginning this troubleshooting procedure until instructed to clear it. Clearing the DTC or resetting the PCM can delete valuable diagnostic information, even if the on-board snapshot and the freeze data are saved.
Inspect for aftermarket fuel system and engine components before beginning troubleshooting.
If any of the DTCs listed below are stored at the same time as P0172, troubleshoot those DTCs first, then recheck for P0172.
P0010, P0011: VTC system

P0087, P0088: Fuel rail pressure sensor

P0101^* , P0102, P0103: MAF sensor

P0107, P0108: MAP sensor

P0133, P1157, P1172^* , P2238, P2252, P2A00: A/F sensor (Sensor 1)

P0134, P0135: A/F sensor (Sensor 1) heater

P0137, P0138, P0139, P2270: Secondary HO2S (Sensor 2)

P0141: Secondary HO2S (Sensor 2) heater

P0201, P0202, P0203, P0204: No. 1-No. 4 cylinder injector(s)

P0443: EVAP canister purge valve

P2646^* , P2647^* , P2648, P2649: VTEC system

*: USA and Canada models

DTC Description	Confirmed DTC	Pending DTC	Freeze Frame
P0172 Fuel System Too Rich

DTC (PGM-FI)

1. Problem verification - Idle:

- 1. Start the engine, and let it idle without load (in P or N).

- 2. Check the parameter(s) below with the HDS.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
AF FB (ST FUEL TRIM)	Less than 0.79

Do the current condition(s) match the threshold?

YES

The AF FB (ST FUEL TRIM) is too low at idle. Go to step 3.

The AF FB (ST FUEL TRIM) is OK at idle. Go to step 2.

2. Problem verification - On-board Snapshot:

- 1. Review the on-board snapshot and record the value of the parameters below when the AF FB (ST FUEL TRIM) was at its lowest point.

ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

On-board Snapshot

- 2. Drive the vehicle according to the conditions determined above.

Signal	Current conditions
Signal	Values	Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

- 3. Check the parameter(s) below with the HDS while driving.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
AF FB (ST FUEL TRIM)	Less than 0.79

Do the current condition(s) match the threshold under the on-board snapshot conditions?

YES

The AF FB (ST FUEL TRIM) is too low under the conditions above. Go to step 3.

The AF FB (ST FUEL TRIM) is OK under the same conditions as the on-board snapshot. The system is normal at this time.

3. Check fuel pressure (low pressure side):

- 1. Start the engine, and let it idle.

- 2. Check the fuel pressure under the conditions when the AF FB (ST FUEL TRIM) is 0.79 or less.

Signal	Current conditions
Signal	Values	Unit
AF FB (ST FUEL TRIM)

Is the fuel pressure between 390-440 kPa (3.98-4.49 kgf/cm² , 56.6-63.8 psi)?

YES

The fuel pressure (low pressure side) is not the cause of the low AF FB (ST FUEL TRIM) value. Go to step 4.

Replace the fuel tank unit .

4. Check fuel pressure (high pressure side):
- 1. Turn the vehicle to the OFF (LOCK) mode.

- 2. Turn the vehicle to the ON mode.

- 3. Clear the DTC with the HDS.

- 4. Start the engine.

- 5. Hold the engine speed at 3, 000 rpm without load (in P or N) until the radiator fan comes on, then let it idle.

- 6. Select the DI FUEL PRESSURE TEST in the INSPECTION MENU with the HDS.

DI FUEL PRESSURE TEST

Does the HDS indicate NORMAL?

YES

The fuel pressure (high pressure side) is OK. Go to step 5.

NO

Go to the troubleshooting for DTC P0087 and DTC P0088 .

5. Replace fuel:

NOTE: There would be an increased likelihood of a fuel related issue if the rich condition appeared shortly after refueling. The MIL DIST (MIL Distance) value in the DATA LIST in combination with the fuel level may help you make this determination.

- 1. Turn the vehicle to the OFF (LOCK) mode.

- 2. Drain the fuel from the fuel tank , then refill the fuel tank with known-good fuel.

- 3. Start the engine, and let it idle.

- 4. Operate the vehicle under the same conditions where the AF FB (ST FUEL TRIM) was 0.79 or less.

ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

On-board Snapshot

Signal	Current conditions
Signal	Values	Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

- 5. Check the parameter(s) below with the HDS while driving.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
AF FB (ST FUEL TRIM)	Less than 0.79

Do the current condition(s) match the threshold under the on-board snapshot conditions?

YES

The fuel is not the cause of the low AF FB (ST FUEL TRIM) value. Go to step 6.

The fuel was causing the low AF FB (ST FUEL TRIM) value.

6. Check MAF sensor reading:

- 1. Continue to let the engine idle.

- 2. Make sure the following conditions are met:

ECT Sensor 1 above 158°F (70°C)
Transmission in P or N
All engine and electrical loads turned off

Signal	Current conditions
Signal	Values	Unit
ECT SENSOR 1

- 3. Monitor the ENGINE SPEED in the DATA LIST with the HDS, then hold the engine speed at 2, 500 rpm with the accelerator pedal held steady.

Signal	Current conditions
Signal	Values	Unit
ENGINE SPEED

- 4. While holding the engine speed at 2, 500 rpm for 30 seconds, check the parameter(s) below with the HDS.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
MAF SENSOR	6.5-9.2	g/s

Do the current condition(s) match the threshold?

YES

The MAF sensor read value is OK. Go to step 7.

The MAF sensor read value is incorrect. Inspect for a cracked, damaged, or incorrectly installed air cleaner assembly. If OK, replace the MAF sensor/IAT sensor .

7. Check engine oil:

- 1. Continue to let the engine idle.

- 2. Gently pinch the PCV vacuum hose (A).

Courtesy of HONDA, U.S.A., INC.

- 3. Check the parameter(s) below with the HDS with the vacuum hose pinched.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
AF FB (ST FUEL TRIM)	Less than 0.79

Do the current condition(s) match the threshold?

YES

The engine oil is OK. Go to step 8.

The engine oil is contaminated. Determine the cause of the contaminated oil (faulty injectors, etc.), then replace the engine oil and oil filter .

8. EVAP canister purge valve check:
- 1. Turn the vehicle to the OFF (LOCK) mode.

- 2. Remove the high pressure fuel pump cover and the fuel bracket .

- 3. Disconnect the following connector.

EVAP canister purge valve 2P connector

- 4. Disconnect the vacuum hose (A) from the EVAP canister purge valve (B) in the engine compartment, and connect a vacuum pump/gauge, 0-30 inHg, to the purge valve.

Courtesy of HONDA, U.S.A., INC.

- 5. Start the engine.

Does the vacuum pump indicate vacuum?

YES

When the climate is warm, fuel vapor from the canister line to the fuel tank enters intake manifold, enriching mixture (excessively rich), causing the engine to stall in some cases. If needed, replace the EVAP canister purge valve .

NO

Go to step 9.

9. Replace A/F sensor (Sensor 1):

- 1. Turn the vehicle to the OFF (LOCK) mode.

- 2. Replace the A/F sensor (Sensor 1) with a known-good sensor .

- 3. Start the engine, and let it idle.

- 4. Operate the vehicle under the same conditions where the AF FB (ST FUEL TRIM) was 0.79 or less.

ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

On-board Snapshot

Signal	Current conditions
Signal	Values	Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

- 5. Check the parameter(s) below with the HDS while driving.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
AF FB (ST FUEL TRIM)	Less than 0.79

Do the current condition(s) match the threshold under the on-board snapshot conditions?

YES

The A/F sensor (Sensor 1) is not the cause of the low AF FB (ST FUEL TRIM) value. Reinstall the original A/F sensor, then go to step 10.

The A/F sensor (Sensor 1) was causing the low AF FB (ST FUEL TRIM) value. Replace the original A/F sensor (Sensor 1) .

10. Replace injectors:

- 1. Turn the vehicle to the OFF (LOCK) mode.

- 2. Replace the injectors with known-good injectors .

- 3. Start the engine, and let it idle.

- 4. Operate the vehicle under the same conditions where the AF FB (ST FUEL TRIM) was 0.79 or less.

ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

On-board Snapshot

Signal	Current conditions
Signal	Values	Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR

- 5. Check the parameter(s) below with the HDS while driving.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
AF FB (ST FUEL TRIM)	Less than 0.79

Do the current condition(s) match the threshold under the on-board snapshot conditions?

YES

The injectors are not the cause of the low AF FB (ST FUEL TRIM) value. Substitute a known-good PCM , then recheck.

The injectors were causing the low AF FB (ST FUEL TRIM) value. Replace all injectors as a set .