DTC P0171

DTC P0171 : Fuel System Too Lean

NOTE:

Before you troubleshoot, review the general troubleshooting information .
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 is 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, P100A, P100B, P100C, P100D: VTC system

P006A, P0101, P0102, P0103: MAF sensor

P0105, P0106, P0107, P0108: MAP sensor

P0130, P0133, P2195, P2237, P2238, P2243, P2245, P2251, P2252, P2A00: A/F sensor (Sensor 1)

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

P0137, P0138, P0139, P2270, P2A01: Secondary HO2S (Sensor 2)

P0141: Secondary HO2S (Sensor 2) heater

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

P0400, P0401, P0404, P0405, P0406, P046C, P049D, P2413: EGR system

P0443: EVAP canister purge valve

P2279: Intake air leakage

P2646, P2647, P2648, P2649: VTEC system

DTC Description	Confirmed DTC	Pending DTC
P0171 Fuel System Too Lean

DTC (PGM-FI)

Problem verification - Idle

-1. Enter the maintenance mode, then 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)	1.30 or more

Data List

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.

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

Data List

-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)	1.30 or more

Data List

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.

Check for debris in MAF sensor
-1. Turn the vehicle to the OFF (LOCK) mode.

-2. Remove the MAF sensor/IAT sensor 1 .

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

Is there debris in MAF sensor/IAT sensor 1?

YES

Remove the debris from the MAF sensor/IAT sensor 1 and then use a vacuum cleaner to remove any debris from the air cleaner housing.

NO

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

Are any components disconnected or damaged?

YES

Repair as necessary.

NO

Go to step 5.

Check PCV system

-1. Enter the maintenance mode, then start the engine and let it idle without load (in P or N).

-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)	1.30 or more

Data List

Do the current condition(s) match the threshold?

YES

The PCV system is not leaking. Go to step 6.

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

Check for Intake manifold vacuum leaks
-1. Turn the vehicle to the OFF (LOCK) mode.

-2. Disconnect the intake air duct from the air cleaner housing.

-3. Connect a large intake manifold adapter cone into the intake air duct from the OTC LeakMaster evaporative emissions system tester kit.

-4. Use the OTC LeakMaster evaporative emissions system tester to direct smoke into the intake manifold.

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 7.

Check MAF sensor reading

-1. Enter the maintenance mode, then start the engine and let it idle without load (in P or N).

Make sure the following conditions are met:

Engine coolant temperature (ECT SENSOR 1) above 158 deg.F (70 deg.C)
Transmission in P or N
All engine and electrical loads turned off

Signal	Current conditions
Signal	Values	Unit
ECT Sensor 1

Data List

-3. Monitor the ENGINE SPEED in the DATA LIST with the HDS, then hold the engine speed at 2500 RPM with the accelerator pedal held steady.

Signal	Current conditions
Signal	Values	Unit
Engine Speed

Data List

-4. While holding the engine speed at 2500 RPM for 30 seconds, check the parameter(s) below with the HDS.

Signal	Threshold		Current conditions
Signal	Values	Unit	Values	Unit
MAF Sensor	2.4-3.4	g/s

Data List

Do the current condition(s) match the threshold?

YES

Go to step 8.

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 1 .

Check fuel pressure

-1. Check the fuel pressure under the conditions when the AF FB (ST FUEL TRIM) is 1.30 or more.

Signal	Current conditions
Signal	Values	Unit
AF FB (ST Fuel Trim)

Data List

Is the fuel pressure within a specified range of fuel pressure test ?

YES

Go to step 9.

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

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. Enter the maintenance mode, then start the engine without load (in P or N).

-4. Operate the vehicle under the same conditions as the on-board snapshot where the AF FB (ST FUEL TRIM) was 1.30 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

Data List

-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)	1.30 or more

Data List

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 10.

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

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. Enter the maintenance mode, then start the engine without load (in P or N).

-4. Operate the vehicle under the same conditions as the on-board snapshot where the AF FB (ST FUEL TRIM) was 1.30 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

Data List

-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)	1.30 or more

Data List

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 (Sensor 1), then go to step 11.

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

Replace injectors

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

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

-3. Enter the maintenance mode, then start the engine without load (in P or N).

-4. Operate the vehicle under the same conditions as the on-board snapshot where the AF FB (ST FUEL TRIM) was 1.30 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

Data List

-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)	1.30 or more

Data List

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 .

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