DTC P0171, P0174

DTC P0171  : Rear Bank (Bank 1) Fuel System Too Lean

DTC P0174  : Front Bank (Bank 2) 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 and/or P0174, troubleshoot those DTCs first, then recheck for P0171 and/or P0174.

  P0087, P0088: Fuel rail pressure sensor

  P006A, P0101, P0102, P0103: MAF sensor

  P0105, P0106, P0107, P0108: MAP sensor

  P0130, P0133, P0153, P1172, P1174, P2195, P2197, P2237, P2238, P2240, P2241, P2243, P2245, P2247, P2249, P2251, P2252, P2254, P2255, P2A00, P2A03: A/F sensor (Sensor 1)

  P0134, P0135, P0154, P0155: A/F sensor (Sensor 1) heater

  P0137, P0138, P0139, P0157, P0158, P0159, P2270, P2272, P2A01, P2A04: Secondary HO2S (Sensor 2)

  P0141, P0161: Secondary HO2S (Sensor 2) heater

  P0201, P0202, P0203, P0204, P0205, P0206: No. 1-No. 6 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, P2651, P2652, P2653, P2654, P2656, P2657, P2658, P2659: VTEC/VCM system

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
   	Values	Unit	Values	Unit
   ST FUEL TRIM B1	More than 1.33
   ST FUEL TRIM B2	More than 1.33

   Do the current condition(s) match the threshold?

   YES 

   The ST FUEL TRIM (B1, B2) is too high at idle. Go to step 3.

   NO 

   The ST FUEL TRIM (B1, B2) 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 ST FUEL TRIM (B1, B2) was at its highest point.

   ENGINE SPEED
   VEHICLE SPEED
   REL TP SENSOR
   APP SENSOR

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

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

   On-board Snapshot

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

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   ST FUEL TRIM B1	More than 1.33
   ST FUEL TRIM B2	More than 1.33

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

   YES 

   The ST FUEL TRIM (B1, B2) is too high under the conditions above. Go to step 3.

   NO 

   The ST FUEL TRIM (B1, B2) 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?

   YES 

   Remove the debris from the MAF 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:

   Visually inspect each of the components below for disconnected hoses, cracks, or damage:

   • Crankcase breather hose (A)
   • Air cleaner housing (B)
   • Intake air duct (C)
   • Oil cap (D) and dipstick (E)

   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
   	Values	Unit	Values	Unit
   ST FUEL TRIM B1	More than 1.33
   ST FUEL TRIM B2	More than 1.33

   Do the current condition(s) match the threshold?

   YES 

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

   NO 

   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
   	Values	Unit	Values	Unit
   ST FUEL TRIM B1	More than 1.33
   ST FUEL TRIM B2	More than 1.33

   Do the current condition(s) match the threshold?

   YES 

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

   NO 

   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.

   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.

   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
   	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.

   '17-19 

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   MAF SENSOR	9.2-13.0	g/s

   '20-23 

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   MAF SENSOR	9.4-13.2	g/s

   Do the current condition(s) match the threshold?

   YES 

   The MAF sensor is OK. Go to step 9.

   NO 

   The MAF sensor is reading incorrectly. 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 ST FUEL TRIM (B1, B2) is 1.33 or more.

   Signal	Current conditions
   	Values	Unit
   ST FUEL TRIM B1
   ST FUEL TRIM B2

   Is the fuel pressure between 410-460 kPa (4.18-4.69 kgf/cm 2, 59.5-66.7 psi)?

   YES 

   The fuel pressure (low pressure side) is OK. Go to step 10.

   NO 

   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 Function Test 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 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 ST FUEL TRIM (B1, B2) was 1.33 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

    -4. Start the engine.

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

    Signal	Threshold		Current conditions
    	Values	Unit	Values	Unit
    ST FUEL TRIM B1	More than 1.33
    ST FUEL TRIM B2	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 ST FUEL TRIM (B1, B2) value. Go to step 12.

    NO 

    The fuel was causing the high ST FUEL TRIM (B1, B2) 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 ST FUEL TRIM (B1, B2) was 1.33 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. Check the parameter(s) below with the HDS while driving.

    Signal	Threshold		Current conditions
    	Values	Unit	Values	Unit
    ST FUEL TRIM B1	More than 1.33
    ST FUEL TRIM B2	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 ST FUEL TRIM (B1, B2) value. Reinstall the original A/F sensor, then go to step 13.

    NO 

    The A/F sensor (Sensor 1) was causing the high ST FUEL TRIM (B1, B2) 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 the ST FUEL TRIM (B1, B2) was 1.33 or more.

    ENGINE SPEED
    VEHICLE SPEED
    REL TP SENSOR
    APP SENSOR

    On-board Snapshot

    Signal	Current conditions
    	Values	Unit
    ENGINE SPEED

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

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

    Signal	Threshold		Current conditions
    	Values	Unit	Values	Unit
    ST FUEL TRIM B1	More than 1.33
    ST FUEL TRIM B2	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 ST FUEL TRIM (B1, B2) value. Substitute a known-good PCM , then recheck.

    NO 

    The injectors were causing the high ST FUEL TRIM (B1, B2) value. Replace all injectors as a set .