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, P04AB: EVAP canister purge valve

  P2279: Intake air leakage

  P2646, P2647, P2648, P2649: VTEC system

DTC (PGM-FI)

1. 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
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	More than 1.30

   Do the current condition (s) match the threshold?

   YES 

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

   NO 

   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 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
   	Values	Unit
   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   -3. With the help of an assistant, check the parameter (s) below with the HDS while driving.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	More than 1.30

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

   YES 

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

   NO 

   AF FB (ST FUEL TRIM) is OK under the same conditions as the on-board snapshot. The system is normal at this time. If the on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the on-board snapshot .

3. Check for debris in MAF sensor

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

   -2. Remove 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 MAF sensor/IAT sensor 1 and then use a vacuum cleaner to remove any debris from the air cleaner housing.

   NO 

   Reinstall MAF sensor/IAT sensor 1 , then go to step 4.

4. Check for disconnected or damaged components:

   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.

   Are any components disconnected or damaged?

   YES 

   Repair the connection or replace damaged part (s).

   NO 

   Go to step 5.

5. Check PCV system

   -1. Enter the maintenance mode, then start the engine .

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

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

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

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	More than 1.30

   Do the current condition (s) match the threshold?

   YES 

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

   NO 

   There is a leak in the PCV system. Check the PCV hose for leaks and repair as needed. If the hose is OK, replace the PCV valve .

6. Check MAF sensor reading

   -1. Hold the engine speed at 3, 000 rpm without load (in P or N) until the radiator fan comes on, then let it idle.

   Make sure the following conditions are met:

   • 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
   	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
   	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
   	Values	Unit	Values	Unit
   MAF Sensor	7.5 - 10.5	g/s

   Do the current condition (s) match the threshold?

   YES 

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

   NO 

   The MAF sensor read value is incorrect. Inspect for a cracked, damaged, or incorrectly installed air cleaner assembly. If OK, replace MAF sensor/IAT sensor 1 .

7. 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 8.

8. Check fuel pressure

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

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

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

   YES 

   The fuel pressure is OK. Go to step 9.

   NO 

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

9. 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 unit, and refill the fuel tank with known-good fuel.

   -3. Enter the maintenance mode, then start the engine .

   -4. Operate the vehicle under the same conditions where 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
   	Values	Unit
   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   -5. With the help of an assistant, check the parameter (s) below with the HDS while driving.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	More than 1.30

   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.

   NO 

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

10. 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 .

    -4. Operate the vehicle under the same conditions where 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
    	Values	Unit
    Engine Speed
    Vehicle Speed
    REL TP Sensor
    APP Sensor

    -5. With the help of an assistant, check the parameter (s) below with the HDS while driving.

    Signal	Threshold		Current conditions
    	Values	Unit	Values	Unit
    AF FB (ST Fuel Trim)	More than 1.30

    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.

    NO 

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

11. 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 .

    -4. Operate the vehicle under the same conditions where 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
    	Values	Unit
    Engine Speed
    Vehicle Speed
    REL TP Sensor
    APP Sensor

    -5. With the help of an assistant, check the parameter (s) below with the HDS while driving.

    Signal	Threshold		Current conditions
    	Values	Unit	Values	Unit
    AF FB (ST Fuel Trim)	More than 1.30

    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.

    NO 

    The injectors were causing the high AF FB (ST FUEL TRIM) value. Replace the original injectors .