DTC P0171: Fuel System Too Lean

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 DTC P0171, troubleshoot those DTCs first, then recheck for P0171.
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
P0171 Fuel System Too Lean

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)	More than 1.33

Do the current condition(s) match the threshold?

YES

The AF FB (ST FUEL TRIM) is too high 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 highest 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)	More than 1.33

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

YES

The AF FB (ST FUEL TRIM) is too high 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 for debris in MAF sensor:
- 1. Turn the vehicle to the OFF (LOCK) mode.

- 2. Remove the MAF sensor/IAT sensor .

- 3. Check for lint, bugs, and other foreign objects in the sensor.

Is there debris in the MAF sensor/IAT sensor?

YES

Remove the debris from the MAF sensor/IAT sensor and then use a vacuum cleaner to remove any debris from the air cleaner housing.

NO

Reinstall the MAF sensor/IAT sensor . Go to step 4.
4. Check for disconnected or damaged components:
- 1. Visually inspect each of the components below for disconnected hoses, cracks, or damage:
- Breather hose (A)
- Air cleaner housing (B)
- Oil cap (C) and dipstick (D)
Courtesy of HONDA, U.S.A., INC.

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

Are any components disconnected or damaged?

YES

Repair as necessary.

NO

Go to step 5.

5. Check brake booster:

- 1. Start the engine and let it idle.

- 2. Pinch the brake booster vacuum hose (A) connected to the intake manifold.

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)	More than 1.33

Do the current condition(s) match the threshold?

YES

The brake booster is not leaking. Go to step 6.

There is a leak in the brake booster or hoses. Check the brake booster vacuum hoses for leaks. If no leaks are found, replace the brake booster .

6. Check PCV system:

- 1. Continue to let the engine idle.

- 2. 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)	More than 1.33

Do the current condition(s) match the threshold?

YES

The PCV system is not leaking. Go to step 7.

There is a leak in the PCV system. Check the vacuum hoses for leaks and repair as needed.

7. Check for Intake manifold vacuum leaks:
- 1. Disconnect the intake air duct from the air cleaner housing.

- 2. Connect a large intake manifold adapter cone into the intake air duct from the OTC LeakMaster evaporative emissions system tester kit.

NOTE: If a large intake manifold adapter cone is not available, leave the intake air duct installed, and remove the brake booster vacuum hose from the brake booster, and inject smoke into the hose.

- 3. Use the OTC LeakMaster evaporative emissions system tester to direct smoke into the intake manifold.

- 4. Inspect each of the areas below for signs of leaks:
- Intake manifold and gaskets
- Throttle body and gasket
- Air intake ducting
- All vacuum and air hoses
Are there any leaks?

YES

Repair the vacuum leak.

NO

Reconnect any disconnected components, then go to step 8.

8. 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 9.

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 .

9. Check fuel pressure (low pressure side):

- 1. Check the fuel pressure under the conditions when the AF FB (ST FUEL TRIM) is 1.33 or more.

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 OK. Go to step 10.

Check the correct power supply and ground for the fuel pump and if both are OK, replace the fuel tank unit .

10. 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.

Does the HDS indicate NORMAL?

YES

The fuel pressure (high pressure side) is OK. Go to step 11.

NO

Go to the troubleshooting for DTC P0087 and DTC P0088 .

11. Replace fuel:

NOTE: There is an increased likelihood of a fuel related issue if the lean 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. Operate the vehicle under the same conditions where the AF FB (ST FUEL TRIM) was 1.33 or more.

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

- 4. Start the engine.

- 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)	More than 1.33

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

YES

The fuel is not the cause of the high AF FB (ST FUEL TRIM) value. Go to step 12.

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

12. 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.

- 4. Operate the vehicle under the same conditions where the AF FB (ST FUEL TRIM) was 1.33 or more.

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)	More than 1.33

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 high AF FB (ST FUEL TRIM) value. Reinstall the original A/F sensor, then go to step 13.

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

13. Replace injectors:

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

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

- 3. Start the engine.

- 4. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.33 or more.

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)	More than 1.33

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

YES

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

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