SFI SYSTEM, Diagnostic DTC:P0171 and P0172

DTC Code DTC Name
P0171 System Too Lean (Bank 1)
P0172 System Too Rich (Bank 1)

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection duration. The fuel trim consists of both the short-term and long-term fuel trims.

The short-term fuel trim is fuel compensation that is used to constantly maintain the air fuel ratio at stoichiometric levels. The signal from the air fuel ratio sensor indicates whether the air fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air fuel ratio is rich and an increase in the fuel injection volume if lean.

Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

MIL

Memory

P0171

System Too Lean (Bank 1)

With a warm engine and stable air fuel ratio feedback, the fuel trim is considerably in error to the lean side (2 trip detection logic).

  • Intake system

  • Fuel injector assembly blockage

  • Mass air flow meter sub-assembly

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leak from exhaust system

  • Open or short in air fuel ratio sensor (sensor 1) circuit

  • Air fuel ratio sensor (sensor 1)

  • PCV valve and hose

  • PCV hose connections

  • Wire harness or connector

  • ECM

Comes on

DTC stored

P0172

System Too Rich (Bank 1)

With a warm engine and stable air fuel ratio feedback, the fuel trim is considerably in error to the rich side (2 trip detection logic).

  • Fuel injector assembly leak or blockage

  • Mass air flow meter sub-assembly

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leak from exhaust system

  • Open or short in air fuel ratio sensor (sensor 1) circuit

  • Air fuel ratio sensor (sensor 1)

  • Wire harness or connector

  • ECM

Comes on

DTC stored
Tip:

  • When DTC P0171 is stored, the actual air fuel ratio is on the lean side. When DTC P0172 is stored, the actual air fuel ratio is on the rich side.

  • If the vehicle runs out of fuel, the air fuel ratio is lean and DTC P0171 may be stored. The MIL is then illuminated.

  • When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is higher than 75°C [167°F]), the system is functioning normally.

MONITOR DESCRIPTION

Under closed loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the fuel injection volumes estimated by the ECM also affect the average fuel trim learned value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learned value of the air fuel ratio). If the average fuel trim learned value exceeds the malfunction thresholds, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

The average fuel trim learned value is +48% or higher, or -35% or less, the ECM interprets this as a fuel system malfunction.

A384580E01

MONITOR STRATEGY

Required Sensors/Components

Fuel system

Frequency of Operation

Continuous

TYPICAL ENABLING CONDITIONS

Fuel system status

Closed loop

Battery voltage

11 V or higher

Either of the following conditions is met

1 or 2

1. Engine speed

Less than 800 rpm

2. Engine load

13.5% or higher

TYPICAL MALFUNCTION THRESHOLDS

Purge-cut

Executing

Either of the following conditions is met

1 or 2

1. Average between short-term fuel trim and long-term fuel trim

48% or higher (varies with engine coolant temperature)

2. Average between short-term fuel trim and long-term fuel trim

-35% or less (varies with engine coolant temperature)

CONFIRMATION DRIVING PATTERN

A288929E16

  1. Connect the GTS to the DLC3.

  2. Turn the ignition switch to ON and turn the GTS on.

  3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).

  4. Turn the ignition switch off and wait for at least 30 seconds.

  5. Turn the ignition switch to ON and turn the GTS on [A].

  6. Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher with all the accessories switched off [B].

  7. With the engine warmed up, idle the engine for 2 minutes or more [C].

  8. Drive the vehicle at a speed between 60 and 100 km/h (37 and 62 mph) for 5 minutes or more [D].

    Note:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

  9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [E].

  10. Read the pending DTCs.

    Tip:

    • If a pending DTC is output, the system is malfunctioning.

    • If a pending DTC is not output, the system is normal.

WIRING DIAGRAM

Refer to DTC P0031 for the air fuel ratio sensor circuit.

Click here

Refer to DTC P0102 for the mass air flow meter sub-assembly circuit.

Click here

CAUTION / NOTICE / HINT

Note:

Inspect the fuses for circuits related to this system before performing the following procedure.

Tip:

  • Sensor 1 refers to the sensor closest to the engine assembly.

  • Sensor 2 refers to the sensor farthest away from the engine assembly.

  • Read freeze frame data using the GTS. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

  • A low air fuel ratio sensor voltage could be caused by a rich air fuel mixture. Check for conditions that would cause the engine to run rich.

  • A high air fuel ratio sensor voltage could be caused by a lean air fuel mixture. Check for conditions that would cause the engine to run lean.

PROCEDURE

  1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    5. Read the DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTC P0171 or P0172 is output

      A

      DTC P0171 or P0172 and other DTCs are output

      B
      Tip:

      If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.

    B

    GO TO DTC CHART

    Click here

    A

  2. CHECK PCV HOSE CONNECTIONS

    1. Check the PCV hose connections.

      Click here

      OK

      PCV valve and hose are connected correctly and are not damaged.

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE PCV HOSE

    OK

  3. CHECK INTAKE SYSTEM

    1. Check the intake system for vacuum leaks.

      Click here

      OK

      No leaks in intake system.

      Tip:

      Perform "Inspection After Repair" after repairing or replacing the intake system.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE INTAKE SYSTEM

    OK

  4. PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

    1. Connect the GTS to the DLC3.

    2. Start the engine.

    3. Turn the GTS on.

    4. Warm up the engine and run the engine at an engine speed of 2500 rpm for approximately 90 seconds.

    5. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.

      Powertrain > Engine and ECT > Active Test

      Active Test Display

      Control the Injection Volume for A/F Sensor

      Data List Display

      AFS Voltage B1S1

      O2S B1S2

    6. Change the fuel injection volume using the GTS, and monitor the output voltage of the air fuel ratio sensor (AFS Voltage B1S1) and heated oxygen sensor (O2S B1S2) displayed on the GTS.

      Tip:

      • The Active Test "Control the Injection Volume for A/F Sensor" can be used to lower the fuel injection volume by 12.5% or increase the injection volume by 12.5%.

      • The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.

      • If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

      Standard

      GTS Display (Sensor)

      Injection Volume

      Status

      Voltage

      AFS Voltage B1S1

      (Air fuel ratio)

      12.5%

      Rich

      Below 3.1 V

      -12.5%

      Lean

      Higher than 3.4 V

      O2S B1S2

      (Heated oxygen)

      12.5%

      Rich

      Higher than 0.55 V

      -12.5%

      Lean

      Below 0.4 V

      Result

      Status AFS Voltage B1S1

      Status O2S B1S2

      Air Fuel Ratio Condition and Air Fuel Ratio Sensor Condition

      Suspected Trouble Area

      Proceed to

      Lean/Rich

      Lean/Rich

      Normal

      -

      A

      Lean

      Lean

      Actual air fuel ratio lean

      • PCV valve and hose

      • PCV hose connections

      • Fuel injector assembly blockage

      • Gas leak from exhaust system

      • Intake system

      • Fuel pressure

      • Mass air flow meter sub-assembly

      • Engine coolant temperature sensor

      Rich

      Rich

      Actual air fuel ratio rich

      • Fuel injector assembly leak or blockage

      • Gas leak from exhaust system

      • Ignition system

      • Fuel pressure

      • Mass air flow meter sub-assembly

      • Engine coolant temperature sensor

      Lean

      Lean/Rich

      Air fuel ratio sensor malfunction

      Air fuel ratio sensor

      B

      Rich

      Lean/Rich

      Air fuel ratio sensor malfunction

      Air fuel ratio sensor

      • Lean: While performing the Active Test "Control the Injection Volume for A/F Sensor", the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently below 0.4 V.

      • Rich: While performing the Active Test "Control the Injection Volume for A/F Sensor", the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently below 3.1 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently higher than 0.55 V.

      • Lean/Rich: While performing the Active Test "Control the Injection Volume for A/F Sensor", the output voltage of the fuel ratio sensor (AFS Voltage B1S1) or heated oxygen sensor (O2S B1S2) alternates correctly.

      Tip:

      Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2].

      Click here

    B

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)Click here

    A

  5. READ VALUE USING GTS (COOLANT TEMP)

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.

      Powertrain > Engine and ECT > Data List

      Tester Display

      Coolant Temp

    5. Read the Data List twice, when the engine is both cold and warmed up.

      Standard

      GTS Display

      Condition

      Specified Condition

      Coolant Temp

      Cold engine

      Same as ambient air temperature

      Warm engine

      Between 75 and 100°C (167 and 212°F)
      Tip:

      Perform "Inspection After Repair" after replacing the engine coolant temperature sensor.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR

    Click here

    OK

  6. READ VALUE USING GTS (MAF)

    1. Connect the GTS to the DLC3.

    2. Start the engine.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / MAF, Coolant Temp and Engine Speed.

      Powertrain > Engine and ECT > Data List

      Tester Display

      Engine Speed

      MAF

      Coolant Temp

    5. Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.

    6. Read MAF with the engine speed at 3000 rpm.

      Standard

      GTS Display

      Condition

      Specified Condition

      MAF

      Shift lever position: N (neutral)

      A/C: Off

      Engine Speed: 3000 rpm

      Between 5.0 gm/sec and 10.0 gm/sec

    Result

    Proceed to

    OK

    NG
    NG

    CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION)Click here

    OK

  7. CHECK FUEL PRESSURE

    1. Check the fuel pressure.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. CHECK FOR EXHAUST GAS LEAK

    1. Check for exhaust gas leaks.

      OK

      No gas leaks.

      Tip:

      Perform "Inspection After Repair" after repairing or replacing the exhaust system.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. INSPECT IGNITION SYSTEM

    1. Inspect the ignition system.

      Click here

      Tip:

      • If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the GTS. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).

      • Perform "Inspection After Repair" after repairing or replacing the ignition system.

        Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

    1. Check the injection and volume.

    Tip:

    • Refer to the fuel injector assembly inspection procedure.

      Click here

    • If the fuel injector assemblies malfunction, engine misfire may occur. The misfire count can be read using the GTS. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).

    • Perform "Inspection After Repair" after replacing the fuel injector assembly.

      Click here

    Result

    Proceed to

    OK

    NG
    OK

    CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)Click here

    NG

    REPLACE FUEL INJECTOR ASSEMBLY

    Click here

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

    Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE AIR FUEL RATIO SENSOR

    Click here

    OK

  12. CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)

    Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - EFI-MAIN RELAY)

    OK

  13. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

    Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  14. REPLACE AIR FUEL RATIO SENSOR

    1. Replace the air fuel ratio sensor.

      Click here

      Tip:

      Perform "Inspection After Repair" after replacing the air fuel ratio sensor.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

  15. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs.

      Powertrain > Engine and ECT > Clear DTCs

    5. Turn the ignition switch off and wait for at least 30 seconds.

    6. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

    7. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    8. Read the DTCs.

      Powertrain > Engine and ECT > Trouble Codes

    Result

    Result

    Proceed to

    DTC P0171 or P0172 is output

    A

    DTCs are not output

    B
    B

    END

    A

  16. CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION)

    1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter sub-assembly and ECM.

      Click here

      Tip:

      Repair any problems.

    Result

    Proceed to

    NEXT
    NEXT

  17. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs.

      Powertrain > Engine and ECT > Clear DTCs

    5. Turn the ignition switch off and wait for at least 30 seconds.

    6. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

    7. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    8. Read the DTCs.

      Powertrain > Engine and ECT > Trouble Codes

    Result

    Result

    Proceed to

    DTC P0171 or P0172 is output

    A

    DTCs are not output

    B
    B

    END

    A

  18. CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY - ECM)

    Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  19. REPLACE MASS AIR FLOW METER SUB-ASSEMBLY

    1. Replace the mass air flow meter sub-assembly.

      Click here

      Tip:

      • If the result of the inspection performed in step 6 (READ VALUE USING GTS (MAF)) indicated no problem, proceed to the next step without replacing the mass air flow meter sub-assembly.

      • Perform "Inspection After Repair" after replacing the mass air flow meter sub-assembly.

        Click here

    Result

    Proceed to

    NEXT
    NEXT

  20. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs.

      Powertrain > Engine and ECT > Clear DTCs

    5. Turn the ignition switch off and wait for at least 30 seconds.

    6. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

    7. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    8. Read the DTCs.

      Powertrain > Engine and ECT > Trouble Codes

    Result

    Result

    Proceed to

    DTCs are not output

    A

    DTC P0171 or P0172 is output

    B
    A

    END

    B

    REPLACE ECM

    Click here