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.

If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.

DTC No. DTC Detection Condition Trouble Area

P0171

P0174

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

  • Air induction system

  • Injector blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leakage from exhaust system

  • Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit

  • Air fuel ratio sensor (bank 1, 2 sensor 1)

  • Air fuel ratio sensor heater (bank 1, 2 sensor 1)

  • Air fuel ratio sensor heater relay

  • Air fuel ratio sensor heater and air fuel ratio sensor heater relay circuits

  • PCV valve and hose

  • PCV hose connections

  • ECM

P0172

P0175

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

  • Injector leakage or blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leakage from exhaust system

  • Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit

  • Air fuel ratio sensor (bank 1, 2 sensor 1)

  • Air fuel ratio sensor heater (bank 1, 2 sensor 1)

  • Air fuel ratio sensor heater relay

  • Air fuel ratio sensor heater and air fuel ratio sensor heater relay circuits

  • ECM

Tech Tips


  • When DTC P0171 or P0174 is set, the actual air fuel ratio is on the lean side. When DTC P0172 or P0175 is set, 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 set. 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 more than 75°C [167°F]), the system is functioning normally.

WIRING DIAGRAM

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Tech Tips

For use of the intelligent tester only:

Malfunctioning areas can be identified by performing the Control the Injection Volume for air fuel ratio sensor function provided in the Active Test. The Control the Injection Volume for air fuel ratio sensor function can help to determine whether the air fuel ratio sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.

The following instructions describe how to conduct the Control the Injection Volume for A/F Sensor operation using the intelligent tester.


  1. Connect the intelligent tester to the DLC3.

  2. Start the engine and turn the tester on.

  3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

  4. Select the following menu items on the tester: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

  5. Perform the Control the Injection Volume for air fuel ratio sensor operation with the engine in an idling condition (press the Right or Left button to change the fuel injection volume).

  6. Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (AFS B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2) 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 25%.

    • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

    Standard voltage
    Tester Display (Sensor) Injection Volume Status Voltage
    AFS B1S1 or AFS B2S1 (Air fuel ratio) +25% Rich Less than 3.0
    AFS B1S1 or AFS B2S1 (Air fuel ratio) -12.5% Lean More than 3.35
    O2S B1S2 or O2S B2S2 (Heated oxygen) +25% Rich More than 0.55
    O2S B1S2 or O2S B2S2 (Heated oxygen) -12.5% Lean Less than 0.4

    Note

    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.

    Case

    Air Fuel Ratio Sensor (Sensor 1)

    Output Voltage

    Heated Oxygen Sensor (Sensor 2)

    Output Voltage

    		 Main Suspected Trouble Area
    1 A017EWCE01 A017EFTE02 -
    2 A017EP5E01 A017EFTE02

    • Air fuel ratio sensor

    • Air fuel ratio sensor heater

    • Air fuel ratio sensor circuit
    3 A017EWCE01 A017EP5E01

    • Heated oxygen sensor

    • Heated oxygen sensor heater

    • Heated oxygen sensor circuit
    4 A017EP5E01 A017EP5E01

    • Fuel pressure

    • Gas leakage from exhaust system

      (Air fuel ratio extremely lean or rich)

    • Following the Control the Injection Volume for air fuel ratio sensor procedure enables technicians to check and graph the voltage outputs of both the air fuel ratio and heated oxygen sensors.

    • The following air fuel ratio control procedure enables the technician to check and graph the voltage output of both the heated oxygen sensors. To display the graph, select the following menu items on the tester: View / Line Graph.

      Tech Tips


      • Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

      • 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, P0172, P0174 OR P0175)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch on (IG) and turn the tester on.

    3. Select the following menu items: Powertrain / Engine and ECT / DTC.

    4. Read the DTCs.

      Result
      Display (DTC Output) Proceed to
      P0171, P0172, P0174 or P0175 A
      P0171, P0172, P0174 or P0175 and other DTCs B

      Tech Tips

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


    B

    GO TO DTC CHART Click here

    A

  2. CHECK PCV HOSE CONNECTIONS

    OK
    PCV hose is connected correctly and is not damaged.

    NG

    REPAIR OR REPLACE PCV HOSE

    OK

  3. CHECK AIR INDUCTION SYSTEM


    1. Check the air induction system for vacuum leakage.

      OK
      No leakage from air induction system.

    NG

    REPAIR OR REPLACE AIR INDUCTION SYSTEM

    OK

  4. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (AIR FUEL RATIO CONTROL)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine and turn the tester on.

    3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

    4. Select the following menu items on the tester: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

    5. Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the Right or Left button to change the fuel injection volume).

    6. Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (AFS B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2) 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 25%.

      • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

      Standard voltage
      Tester Display (Sensor) Injection Volume Status Voltage
      AFS B1S1 or AFS B2S1 (Air fuel ratio) +25% Rich Less than 3.0
      AFS B1S1 or AFS B2S1 (Air fuel ratio) -12.5% Lean More than 3.35
      O2S B1S2 or O2S B2S2 (Heated oxygen) +25% Rich More than 0.55
      O2S B1S2 or O2S B2S2 (Heated oxygen) -12.5% Lean Less than 0.4
      Result
      Status AFS B1S1 or AFS B2S1 Status O2S B1S2 or O2S B2S2 Air fuel ratio condition and air fuel ratio sensor condition Misfire Suspected Trouble Area Proceed to
      Lean/Rich Lean/Rich Normal - - C
      Lean Lean Actual air fuel ratio lean May occur

      • PCV valve and hose

      • PCV hose connections

      • Injector blockage

      • Gas leakage from exhaust system

      • Air induction system

      • Fuel pressure

      • Mass air flow meter

      • Engine coolant temperature sensor

      		 A
      Rich Rich Actual air fuel ratio rich -

      • Injector leakage or blockage

      • Gas leakage 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 Control the Injection Volume for A/F Sensor, the air fuel ratio sensor output voltage (AFS) is consistently more than 3.35 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.

      Rich: During Control the Injection Volume for A/F Sensor, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.55 V.

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


    B

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

    C

    PERFORM CONFIRMATION DRIVING PATTERN Click here

    A

  5. READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch on (IG) and turn the tester on.

    3. Select the following menu items: Powertrain / Engine and ECT / Data List / Coolant Temp.

    4. Read the 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 95°C (167°F and 203°F)

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  6. READ VALUE USING INTELLIGENT TESTER (MASS AIR FLOW)


    1. Read the values using intelligent tester (mass air flow).

      Note


      • Turn the ignition switch off.

      • Perform the inspection with the vehicle indoors and on a level surface.

      • Perform the inspection of the mass air flow meter while it is installed in the air cleaner case (installed on the vehicle).

      • During the test, do not use the exhaust air duct to perform suction on the exhaust pipe.


      1. Turn the ignition switch on (IG) (do not start the engine).

      2. Turn the tester on.

      3. Select the following menu items: Select: Powertrain / Engine and ECT / Data List / MAF.

      4. Wait for 30 seconds, and read the values on the tester.

        Standard value
        Less than 0.69 g/sec

    2. Inspect the mass air flow meter.


      1. Remove the mass air flow meter Click here.

      2. Using a work light, check that the platinum filament (heater portion) in the mass air flow meter has no foreign matter attached.

        A017EOHE03
        OK
        No foreign matter attached.

      3. Reinstall the mass air flow meter Click here.


    NG

    REPLACE MASS AIR FLOW METER Click here

    OK

  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. CHECK FOR EXHAUST GAS LEAKAGE

    OK
    No gas leakage

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK FOR SPARKS AND IGNITION


    1. Check for sparks and ignition Click here.

      Tech Tips

      If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the intelligent tester. Select the following menu items: Powertrain / Engine and ECT / Data List / Cylinder #1 to #6 Misfire Rate.


    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Inspect the fuel injector assembly Click here.

      Tech Tips

      If the injectors malfunction, engine misfire may occur. The misfire count can be read using the intelligent tester. Select the following menu items: Powertrain / Engine and ECT / Data List / Cylinder #1 to #6 Misfire Rate.


    NG

    REPLACE FUEL INJECTOR ASSEMBLY Click here

    OK

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. A017D8BE39

      Disconnect the air fuel ratio sensor connector.

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

      Standard resistance
      Bank 1
      Tester Connection Condition Specified Condition
      B20-1 (HA1A) - B20-2 (+B) 20°C (68°F) 1.8 to 3.4 Ω
      B20-1 (HA1A) - B20-4 (A1A-) Always 10 kΩ or higher
      Bank 2
      Tester Connection Condition Specified Condition
      B19-1 (HA2A) - B19-2 (+B) 20°C (68°F) 1.8 to 3.4 Ω
      B19-1 (HA2A) - B19-4 (A2A-) Always 10 kΩ or higher

    3. Reconnect the air fuel ratio sensor connector.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

  12. INSPECT TERMINAL VOLTAGE (+B TERMINAL OF AIR FUEL RATIO SENSOR)


    1. A017CWXE01

      Disconnect the air fuel ratio sensor connector.

    2. Turn the ignition switch on (IG).

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

      Standard voltage
      Bank 1
      Tester Connection Condition Specified Condition
      B20-2 (+B) - Body ground Ignition switch on (IG) 9 to 14 V
      Bank 2
      Tester Connection Condition Specified Condition
      B19-2 (+B) - Body ground Ignition switch on (IG) 9 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


    NG

    INSPECT FUSE (A/F FUSE) Click here

    OK

  13. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)


    1. A017BYFE13

      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 (Check for open)
      Bank 1
      Tester Connection Condition Specified Condition
      B20-3 (A1A+) - B2-22 (A1A+) Always Below 1 Ω
      B20-4 (A1A-) - B2-30 (A1A-) Always Below 1 Ω
      Bank 2
      Tester Connection Condition Specified Condition
      B19-3 (A2A+) - B2-23 (A2A+) Always Below 1 Ω
      B19-4 (A2A-) - B2-31 (A2A-) Always Below 1 Ω
      Standard resistance (Check for short)
      Bank 1
      Tester Connection Condition Specified Condition
      B20-3 (A1A+) or B2-22 (A1A+) - Body ground Always 10 kΩ or higher
      B20-4 (A1A-) or B2-30 (A1A-) - Body ground Always 10 kΩ or higher
      Bank 2
      Tester Connection Condition Specified Condition
      B19-3 (A2A+) or B2-23 (A2A+) - Body ground Always 10 kΩ or higher
      B19-4 (A2A-) or B2-31 (A2A-) - Body ground Always 10 kΩ or higher

    4. Reconnect the ECM connector.

    5. Reconnect the air fuel ratio sensor connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  14. REPLACE AIR FUEL RATIO SENSOR


    NEXT

  15. PERFORM CONFIRMATION DRIVING PATTERN


    1. Connect the intelligent tester to the DLC3 (Procedure A).

    2. Turn the ignition switch on (IG) and turn the tester on (Procedure B).

    3. Clear the DTCs Click here (Procedure C).

    4. Select the check mode using the tester Click here (Procedure D).

    5. Start the engine and warm it up with all the accessories switched off (Procedure E).

    6. Drive the vehicle at between 60 km/h and 120 km/h (38 mph and 75 mph) and at an engine speed of between 1400 rpm and 3200 rpm for 3 to 5 minutes (Procedure F).

      A017DWNE02

      Tech Tips

      If the system is still malfunctioning, the MIL will be illuminated during procedure "F".

      Note

      If the conditions in this test are not strictly followed, no malfunction will be detected.


    NEXT

  16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)


    1. Select the following menu items: Powertrain / Engine and ECT / DTC.

    2. Read the DTCs.

      Result
      Display (DTC Output) Proceed to
      No output A
      P0171, P0172, P0174 or P0175 B

    B

    REPLACE ECM Click here

    A

    END

  17. INSPECT FUSE (A/F FUSE)


    1. A017ENJE01

      Remove the air fuel ratio fuse from the engine room relay block.

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

      Standard resistance
      EFI Connection Condition Specified Condition
      Air fuel ratio fuse Always Below 1 Ω

    3. Reinstall the air fuel ratio fuse.


    NG

    REPLACE FUSE

    OK

  18. INSPECT ENGINE ROOM JUNCTION BLOCK ASSEMBLY (A/F RELAY)


    1. Inspect the A/F relay Click here.


    NG

    REPLACE ENGINE ROOM JUNCTION BLOCK ASSEMBLY

    OK

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F FUSE - AIR FUEL RATIO SENSOR)