SFI SYSTEM, Diagnostic DTC:P0171, P0172, P0174, P0175

DTC Code DTC Name
P0171 System Too Lean (Bank 1)
P0172 System Too Rich (Bank 1)
P0174 System Too Lean (Bank 2)
P0175 System Too Rich (Bank 2)

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. 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 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

P0174

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 blockage

  • Mass air flow meter

  • 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)

  • Air fuel ratio sensor heater (Sensor 1)

  • Integration relay

  • Air fuel ratio sensor heater and integration relay circuits

  • PCV valve and hose

  • PCV hose connections

  • ECM

  • Wire harness or connector

P0172

P0175

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 leakage or blockage

  • Mass air flow meter

  • 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)

  • Air fuel ratio sensor heater (Sensor 1)

  • Integration relay

  • Air fuel ratio sensor heater and integration relay circuits

  • ECM

Tech Tips


  • When DTC P0171 or P0174 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 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 or P0174 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 ECM estimated fuel injection volumes 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 threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

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

A0158YPE01

CONFIRMATION DRIVING PATTERN

A015CO6E44

  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 operation).

  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 135 km/h (38 and 85 mph) for 5 minutes or more [D].

    CAUTION:

    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.

    Tech Tips

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

WIRING DIAGRAM

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Tech Tips


  • Read freeze frame data using the GTS. 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.

  • 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.

  • Bank 1 refers to the bank that includes the No. 1 cylinder*.

    *: The No. 1 cylinder is the cylinder which is farthest from the transmission.

  • Bank 2 refers to the bank that does not include the No. 1 cylinder.

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

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

PROCEDURE


  1. CHECK FOR ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175)


    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.

      Result
      Result Proceed to
      P0171, P0172, P0174 or P0175 is output A
      P0171, P0172, P0174 or P0175 and other DTCs are output B

      Tech Tips

      If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.


    B
    A
  2. CHECK PCV HOSE CONNECTIONS


    1. Check the PCV hose (w/ secondary air injection system) connections Click here.

    2. Check the PCV hose (w/o secondary air injection system) connections Click here.

      OK
      PCV hose is connected correctly and is not damaged.

    NG
    OK
  3. CHECK INTAKE SYSTEM


    1. Check the intake system for vacuum leaks Click here.

      OK
      No leaks in intake system.

    NG
    OK
  4. PERFORM ACTIVE TEST USING GTS (INJECTION VOLUME)


    1. Connect the GTS to the DLC3.

    2. Start the engine.

    3. Turn the GTS on.

    4. 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.

    6. Perform the Control the Injection Volume for A/F Sensor operation with the engine idling.

    7. Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the GTS.

      Tech Tips


      • Change the fuel injection volume within the range of -12.5% to +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.

      GTS Display (Sensor) Injection Volume Status Voltage

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio)

      +12.5% Rich Below 3.1 V

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio)

      -12.5% Lean Higher than 3.4 V

      O2S B1S2 or O2S B2S2

      (Heated oxygen)

      +12.5% Rich Higher than 0.55 V

      O2S B1S2 or O2S B2S2

      (Heated oxygen)

      -12.5% Lean Below 0.4 V
      Result
      Status of AFS Voltage B1S1 or AFS Voltage B2S1 Status of O2S B1S2 or O2S B2S2 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 leaks from exhaust system

      • Intake system

      • Fuel pressure

      • Mass air flow meter

      • Engine coolant temperature sensor

      A
      Rich Rich Actual air fuel ratio rich
      • Fuel injector assembly leakage or blockage

      • Gas leaks from exhaust system

      • Ignition system

      • Fuel pressure

      • Mass air flow meter

      • Engine coolant temperature sensor

      A
      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 B

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

      Rich: During the Control the Injection Volume for A/F Sensor Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.

      Lean/Rich: During the Control the Injection Volume for A/F Sensor Active Test, the output voltage of the heated oxygen sensor alternates correctly.

      Tech Tips

      Refer to "Data List / Active Test" [AFS Voltage B1S1, AFS Voltage B2S1, O2S B1S2 and O2S B2S2] Click here.


    B
    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.

    5. Read Coolant Temp twice, when the engine is both cold and warmed up.

      Standard
      With cold engine: Same as ambient air temperature.
      With warm engine: Between 75°C and 100°C (167°F and 212°F).

    NG
    OK
  6. READ VALUE USING GTS (MAF)


    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 / MAF and 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
      Between 18.3 gm/s and 25.8 gm/s (shift lever: N; A/C: off).

    NG
    OK
  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG
    OK
  8. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leaks.

      OK
      No gas leaks.

    NG
    OK
  9. CHECK FOR SPARKS AND IGNITION


    1. Perform a spark test Click here.

      Tech Tips

      If the result of the spark test is normal, proceed to the next step.


    NEXT
  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Check the injection and volume Click here.


    OK
    NG
  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. Inspect the air fuel ratio sensor Click here.


    NG
    OK
  12. CHECK TERMINAL VOLTAGE (+B OF AIR FUEL RATIO SENSOR)

    A0155WXE64
    Text in Illustration
    *A for Bank 1 Sensor 1
    *B for Bank 2 Sensor 1
    *a

    Front view of wire harness connector

    (to Air Fuel Ratio Sensor)


    1. Disconnect the air fuel ratio sensor connector.

    2. Turn the ignition switch to ON.

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      C22-2 (+B) - Body ground Ignition switch ON 11 to 14 V
      C23-2 (+B) - Body ground Ignition switch ON 11 to 14 V

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


    1. Disconnect the air fuel ratio sensor connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance
      for LHD
      Tester Connection Condition Specified Condition
      C22-1 (HA1A) - C45-22 (HA1A) Always Below 1 Ω
      C22-3 (A1A+) - C45-126 (A1A+) Always Below 1 Ω
      C22-4 (A1A-) - C45-125 (A1A-) Always Below 1 Ω
      C23-1 (HA2A) - C45-20 (HA2A) Always Below 1 Ω
      C23-3 (A2A+) - C45-103 (A2A+) Always Below 1 Ω
      C23-4 (A2A-) - C45-102 (A2A-) Always Below 1 Ω
      C22-1 (HA1A) or C45-22 (HA1A) - Body ground Always 10 kΩ or higher
      C22-3 (A1A+) or C45-126 (A1A+) - Body ground Always 10 kΩ or higher
      C22-4 (A1A-) or C45-125 (A1A-) - Body ground Always 10 kΩ or higher
      C23-1 (HA2A) or C45-20 (HA2A) - Body ground Always 10 kΩ or higher
      C23-3 (A2A+) or C45-103 (A2A+) - Body ground Always 10 kΩ or higher
      C23-4 (A2A-) or C45-102 (A2A-) - Body ground Always 10 kΩ or higher
      for RHD
      Tester Connection Condition Specified Condition
      C22-1 (HA1A) - C46-22 (HA1A) Always Below 1 Ω
      C22-3 (A1A+) - C46-126 (A1A+) Always Below 1 Ω
      C22-4 (A1A-) - C46-125 (A1A-) Always Below 1 Ω
      C23-1 (HA2A) - C46-20 (HA2A) Always Below 1 Ω
      C23-3 (A2A+) - C46-103 (A2A+) Always Below 1 Ω
      C23-4 (A2A-) - C46-102 (A2A-) Always Below 1 Ω
      C22-1 (HA1A) or C46-22 (HA1A) - Body ground Always 10 kΩ or higher
      C22-3 (A1A+) or C46-126 (A1A+) - Body ground Always 10 kΩ or higher
      C22-4 (A1A-) or C46-125 (A1A-) - Body ground Always 10 kΩ or higher
      C23-1 (HA2A) or C46-20 (HA2A) - Body ground Always 10 kΩ or higher
      C23-3 (A2A+) or C46-103 (A2A+) - Body ground Always 10 kΩ or higher
      C23-4 (A2A-) or C46-102 (A2A-) - Body ground Always 10 kΩ or higher

    NG
    OK
  14. REPLACE AIR FUEL RATIO SENSOR


    1. Replace the air fuel ratio sensor Click here.


    NEXT
  15. PERFORM CONFIRMATION DRIVING PATTERN


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs Click here.

    5. Turn the ignition switch off.

    6. Turn the ignition switch to ON and turn the GTS 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 / Trouble Codes.

    10. Read the DTCs.

      Result
      Result Proceed to
      DTC P0171, P0172, P0174 or P0175 is output A
      No DTC is output B

    B
    A
  16. CHECK HARNESS AND CONNECTOR


    1. Check the connection and terminal contact pressure of the connectors and wire harnesses between the mass air flow meter and ECM Click here.

      Tech Tips

      Repair any problems.


    NEXT
  17. CHECK WHETHER DTC OUTPUT RECURS


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs Click here.

    5. Turn the ignition switch off.

    6. Turn the ignition switch to ON and turn the GTS 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 / Trouble Codes.

    10. Read the DTCs.

      Result
      Result Proceed to
      DTC P0171, P0172, P0174 or P0175 is output A
      No DTC is output B

    B
    A
  18. CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)


    1. Disconnect the mass air flow meter connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance
      for LHD
      Tester Connection Condition Specified Condition
      C50-5 (VG) - C45-74 (VG) Always Below 1 Ω
      C50-4 (E2G) - C45-75 (E2G) Always Below 1 Ω
      C50-5 (VG) or C45-74 (VG) - Body ground Always 10 kΩ or higher
      for RHD
      Tester Connection Condition Specified Condition
      C50-5 (VG) - C46-74 (VG) Always Below 1 Ω
      C50-4 (E2G) - C46-75 (E2G) Always Below 1 Ω
      C50-5 (VG) or C46-74 (VG) - Body ground Always 10 kΩ or higher

    NG
    OK
  19. REPLACE MASS AIR FLOW METER


    1. Replace the mass air flow meter Click here.

      Tech Tips

      If the result of the inspection performed in step 6 indicated no problem, proceed to the next step without replacing the mass air flow meter.


    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 Click here.

    5. Turn the ignition switch off.

    6. Turn the ignition switch to ON and turn the GTS 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 / Trouble Codes.

    10. Read the DTCs.

      Result
      Result Proceed to
      No DTC is output A
      DTC P0171, P0172, P0174 or P0175 is output B

    B
    A
  21. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY)


    1. Disconnect the air fuel ratio sensor connector.

    2. Remove the integration relay from the engine room relay block.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      C22-2 (+B) - 1A-4 Always Below 1 Ω
      C23-2 (+B) - 1A-4 Always Below 1 Ω
      1A-2 - 1B-4 Always Below 1 Ω
      1A-3 - Body ground Always Below 1 Ω
      C22-2 (+B) or 1A-4 - Body ground Always 10 kΩ or higher
      C23-2 (+B) or 1A-4 - Body ground Always 10 kΩ or higher
      1A-2 or 1B-4 - Body ground Always 10 kΩ or higher

    NG
    OK
  22. INSPECT INTEGRATION RELAY (A/F)


    1. Inspect the integration relay (A/F) Click here.


    NG
    OK