SFI SYSTEM, Diagnostic DTC:P0171, P0172

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

DESCRIPTION

The fuel trim relates to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and the long-term fuel trim.

The short-term fuel trim is the short-term fuel compensation used to maintain the air fuel ratio at its ideal theoretical value. The signal from the heated oxygen sensor indicates whether the air fuel ratio is rich or lean compared to the ideal theoretical value, triggering a reduction in the fuel volume if the air fuel ratio is rich, and an increase in the fuel volume if it is 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. DTC Detection Condition Trouble Area
P0171 When air fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on lean side (3 trip detection logic)

  • Fuel injector assembly blockage

  • Manifold absolute pressure sensor

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leak from exhaust system

  • Open or short in heated oxygen sensor circuit

  • Heated oxygen sensor

  • ECM
P0172 When air fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on rich side (3 trip detection logic)

  • Fuel injector assembly blockage

  • Manifold absolute pressure sensor

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leak from exhaust system

  • Open or short in heated oxygen sensor circuit

  • Heated oxygen sensor

  • ECM

Tech Tips


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

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

  • If the total of the short-term fuel trim value and long-term fuel trim value is within 20%, the system functions normally.

  • When the air fuel learning value is 1.23 or more, DTC P0171 is stored.

  • When the air fuel learning value is 0.77 or less, DTC P0172 is stored.

WIRING DIAGRAM

A01VILOE01

CONFIRMATION DRIVING PATTERN

CAUTION:

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

These DTCs are detected when the vehicle is driven for approximately 20 minutes at a constant vehicle speed of between 80 km/h (50 mph) and 110 km/h (70 mph) with the transmission gear selector lever in the 5th position (a malfunction is detected if the learning value of the driving range deviates by 25 %).

CAUTION / NOTICE / HINT

Note


  • Perform electronic throttle learning after replacing the ECM Click here.

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

Tech Tips


  • 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 intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. 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.

PROCEDURE


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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

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

    5. Read DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 is output A
      DTC P0171 or P0172 and other DTCs are output B

      Tech Tips

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


    B

    GO TO DTC CHART Click here

    A

  2. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine.

    3. Turn the tester on.

    4. Warm up the engine at an engine speed of 2500 rpm for approximately 3 minutes.

    5. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

    6. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).

    7. Monitor the voltage output of the heated oxygen sensor and No. 2 heated oxygen sensor (O2S B1S1 and O2S B1S2) displayed on the tester.

      Tech Tips


      • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.

      • The heated oxygen sensor has an output delay of a few seconds and the No. 2 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.

      Result
      The heated oxygen sensors reacts in accordance with increases and decreases of the fuel injection volume:
      +12.5% = Rich output
      Higher than 0.55 V
      -12.5% = Lean output
      Below 0.4 V
      A01VITXE01

      The following procedure enables the technician to check and graph the voltage outputs of both the heated oxygen sensors.

      To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / O2S B1S1 and O2S B1S2; then press the view button.

      Tech Tips

      If the vehicle is short of fuel, the air fuel ratio becomes lean and the heated oxygen sensor DTCs are recorded, and then the MIL illuminates.

      Result
      Result Proceed to
      Case 3 A
      Case 2 B
      Case 1 C

    B

    CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM) Click here

    C

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

    A

  3. READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

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

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

      Standard
      Tester Display Condition Specified Condition
      Coolant Temp Cold engine Same as ambient air temperature
      Warm engine Between 75 and 100°C (167 and 212°F)

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  4. READ VALUE USING INTELLIGENT TESTER (MAP)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

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

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

    6. Read the MAP value at idling and 2500 rpm.

      Standard Value
      Condition Specified Condition

      Ignition switch ON

      (Engine not running)

      		 80 to 110 kPa

      Idling

      (Shift lever in Neutral position and A/C OFF)

      		 28 to 48 kPa

      2500 rpm

      (Shift lever in Neutral position and A/C OFF)

      		 22 to 50 kPa

    NG

    REPLACE MANIFOLD ABSOLUTE PRESSURE SENSOR Click here

    OK

  5. CHECK SPARK AND IGNITION


    1. Perform a spark test.

      Tech Tips


      • Refer to the ignition system on-vehicle inspection Click here.

      • If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the tester. Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 Misfire Count (to Cylinder #3 Misfire Count).


    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  6. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leak.

      OK
      No gas leak.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Check the injector volume.

      Tech Tips


      • Refer to the fuel injector assembly inspection procedure Click here.

      • If the fuel injectors malfunction, engine misfire may occur. The misfire count can be read using the tester. Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 Misfire Count (to Cylinder #3 Misfire Count).


    NG

    REPLACE FUEL INJECTOR ASSEMBLY Click here

    OK

  9. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM)


    1. Disconnect the heated oxygen sensor connector.

    2. Disconnect the ECM connector.

    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance
      Tester Connection Condition Specified Condition
      B37-3 (OX1A) - B87-34 (OX1A) Always Below 1 Ω
      B37-1 (HT1A) - B87-2 (HT1A) Always Below 1 Ω
      B37-4 (E1) - B87-32 (E2) Always Below 1 Ω
      B37-3 (OX1A) or B87-34 (OX1A) - Body ground Always 10 kΩ or higher
      B37-1 (HT1A) or B87-2 (HT1A) - Body ground Always 10 kΩ or higher

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  10. REPLACE HEATED OXYGEN SENSOR


    1. Replace heated oxygen sensor Click here.


    NEXT

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

    4. Clear DTCs Click here.

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

    6. Turn the tester on.

    7. Start the engine and warm it up.

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

    9. Enter the following menus: Powertrain / Engine and ECT / DTC.

    10. Read the pending DTCs.

      Result
      Result Proceed to
      DTC is not output A
      DTC P0171 or P0172 is output B

    A

    END

    B

    REPLACE ECM Click here