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

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 trim 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

With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to lean side

(2 trip detection logic)

  • Intake system

  • Fuel injector assembly

  • Mass air flow meter sub-assembly

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leaks from exhaust system

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

  • Air fuel ratio sensor (bank 1 sensor 1)

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

  • Air fuel ratio sensor heater circuit (bank 1 sensor 1)

  • PCV valve and hose

  • PCV hose connections

  • Wire harness or connector

  • ECM
P0172

With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to rich side

(2 trip detection logic)

  • Fuel injector assembly

  • Mass air flow meter sub-assembly

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leaks from exhaust system

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

  • Air fuel ratio sensor (bank 1 sensor 1)

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

  • Air fuel ratio sensor heater circuit (bank 1 sensor 1)

  • Wire harness or connector

  • ECM

Tech Tips


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

MONITOR DESCRIPTION

Under closed-loop fuel control, a fuel injection volume that deviates from that estimated by the ECM causes 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 value. Deviations from the ECM's estimated fuel injection volume also affects the average fuel trim learning value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air fuel ratio). If the average fuel trim learning value exceeds a malfunction threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.

Example:

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

A019LRKE27

CONFIRMATION DRIVING PATTERN

A019KL9E50

  1. Connect the intelligent tester to the DLC3.

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

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

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

  5. Turn the engine switch on (IG) and turn the tester 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 (37 and 84 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 / DTC [E].

  10. Read the Pending DTCs.

    Tech Tips

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

WIRING DIAGRAM

Refer to DTC P0102 Click here.

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Tech Tips

Malfunctioning areas can be identified by performing the Control the Injection Volume function provided in the Active Test. The Control the Injection Volume 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 operation using the intelligent tester.


  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 90 seconds.

  5. Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume.

  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 output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

Tech Tips


  • Change the fuel injection volume within the range of -12% to +12%. The injection volume can be changed in fine gradations.

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

Tester Display (Sensor) Injection Volume Status Voltage

AFS Voltage B1S1

(Air fuel ratio)

 +12% Rich Below 3.1 V
-12% Lean Higher than 3.4 V

O2S B1S2

(Heated oxygen)

 +12% Rich Higher than 0.55 V
-12% Lean Below 0.4 V

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 A019L7QE05 A019OABE08 A019L7QE05 A019O5QE06 -
2 A019L7QE05 A019MDPE01 A019L7QE05 A019O5QE06

  • Air fuel ratio sensor

  • Air fuel ratio sensor heater

  • Air fuel ratio sensor circuit
3 A019L7QE05 A019OABE08 A019L7QE05 A019MDPE01

  • Heated oxygen sensor

  • Heated oxygen sensor heater

  • Heated oxygen sensor circuit
4 A019L7QE05 A019MDPE01 A019L7QE05 A019MDPE01

  • Fuel injector assembly

  • Fuel pressure

  • Gas leak from exhaust system (Air fuel ratio extremely rich or lean)

Note

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

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.

  • 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 ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

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

    5. Read the 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. CHECK PCV HOSE CONNECTIONS


    1. Check the PCV hose connections Click here.

      OK
      PCV hose is connected correctly and is not damaged.

    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.

    NG

    REPAIR OR REPLACE INTAKE SYSTEM

    OK

  4. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME)


    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 90 seconds.

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

    6. Perform the Control the Injection Volume operation with the engine idling.

    7. Monitor the voltage outputs of the air fuel ratio sensor and the heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

      Tech Tips


      • Change the fuel injection volume within the range of -12% and +12%. The injection volume can be changed in fine gradations.

      • 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

      Tester Display

      (Sensor)

      		 Injection Volume Status Voltage

      AFS Voltage B1S1

      (Air fuel ratio)

      		 +12% Rich Less than 3.1 V
      -12% Lean More than 3.4 V

      O2S B1S2

      (Heated oxygen)

      		 +12% Rich More than 0.55 V
      -12% Lean Less than 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

      		 A
      Rich Rich Actual air fuel ratio rich

      • Fuel injector assembly 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: During the Control the Injection Volume Active Test, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently more than 3.4 V, and the heated oxygen sensor output voltages (O2S B1S2) is consistently less than 0.4 V.

      Rich: During Control the Injection Volume of the Active Test, the AFS Voltage B1S1 is consistently less than 3.1 V, and the O2S B1S2 is consistently more than 0.55 V.

      Lean/Rich: During the Control the Injection Volume Active Test, the output voltage of the air fuel ratio sensor and heated oxygen sensor alternates correctly.

      Tech Tips

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


    B

    Click here

    A

  5. READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

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

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

      Standard value
      With cold engine:
      Same as ambient air temperature.
      With warm engine:
      Between 75°C and 100°C (176°F and 212°F).

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  6. READ VALUE USING INTELLIGENT TESTER (MAF)


    1. Connect the tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

    4. Enter the following menus: Powertrain / Engine / 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 8.4 g/sec. and 12.6 g/sec. (shift lever: Neutral position, A/C: Off).

    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.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leaks.

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK FOR SPARKS AND IGNITION


    1. Perform a spark test Click here.

      CAUTION:

      Always disconnect all the injector connectors.

      Note

      Do not crank the engine for more than 2 seconds.

      OK
      Spark jumps across electrode gap.

    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Check the injection and volume Click here.


    OK

    PERFORM CONFIRMATION DRIVING PATTERN Click here

    NG

    REPLACE FUEL INJECTOR ASSEMBLY Click here

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. A019N7XE15
      Text in Illustration
      *a

      Component without harness connected

      (Air Fuel Ratio Sensor)

      Disconnect the air fuel ratio sensor connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      1 (HA1A) - 2 (+B) 20°C (68°F) 1.6 to 3.2 Ω
      1 (HA1A) - 4 (A1A-) Always 10 kΩ or higher

    3. Reconnect the air fuel ratio sensor connector.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

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


    1. A019N7GE30
      Text in Illustration
      *a

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor)

      Disconnect the air fuel ratio sensor connector.

    2. Turn the engine switch on (IG).

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

      Standard Voltage
      Tester Connection Condition Specified Condition
      D20-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


    NG

    Click here

    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 (Check for Open)
      Tester Connection Condition Specified Condition
      D20-1 (HA1A) - D44-18 (HA1A) Always Below 1 Ω
      D20-3 (A1A+) - D44-103 (A1A+) Always Below 1 Ω
      D20-4 (A1A-) - D44-126 (A1A-) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      D20-1 (HA1A) or D44-18 (HA1A) - Body ground Always 10 kΩ or higher
      D20-3 (A1A+) or D44-103 (A1A+) - Body ground Always 10 kΩ or higher
      D20-4 (A1A-) or D44-126 (A1A-) - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reconnect the ECM connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

    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 intelligent tester to the DLC3.

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

    3. Clear the DTCs Click here.

    4. Turn the engine switch off.

    5. Turn the engine switch on (IG) and turn the tester on.

    6. Start the engine and warm it up.

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

    8. Enter the following menus: Powertrain / Engine / DTC.

    9. Read the pending DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 is output A
      DTC is 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.

      Tech Tips

      Repair any problems.


    NEXT

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs Click here.

    5. Turn the engine switch off.

    6. Turn the engine switch on (IG) and turn the tester on.

    7. Start the engine and warm it up.

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

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

    10. Read the Pending DTCs.

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

    B

    END

    A

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


    1. Disconnect the mass air flow meter sub-assembly connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      D3-5 (VG) - D44-94 (VG) Always Below 1 Ω
      D3-4 (E2G) - D44-117 (E2G) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      D3-5 (VG) or D44-94 (VG) - Body ground Always 10 kΩ or higher

    4. Reconnect the mass air flow meter sub-assembly connector.

    5. Reconnect the ECM connector.


    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.

      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 sub-assembly.


    NEXT

  20. CHECK WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs Click here.

    5. Turn the engine switch off.

    6. Turn the engine switch on (IG) and turn the tester on.

    7. Start the engine and warm it up.

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

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

    10. Read the Pending DTCs.

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

    B

    END

    A

    REPLACE ECM Click here

  21. INSPECT INTEGRATION RELAY (EFI MAIN NO. 2 RELAY)


    1. Inspect the integration relay (EFI MAIN No. 2 relay) Click here.


    NG

    REPLACE INTEGRATION RELAY (EFI MAIN NO. 2 RELAY) Click here

    OK

  22. CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY - BODY GROUND)


    1. Remove the integration relay from the engine room relay block and junction block assembly.

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

      Standard Voltage
      Tester Connection Condition Specified Condition
      3A-1 - Body ground Engine switch on (IG) 11 to 14 V

    3. Reinstall the integration relay.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (BATTERY - INTEGRATION RELAY)

    OK

  23. CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY - AIR FUEL RATIO SENSOR)


    1. Disconnect the air fuel ratio sensor connector.

    2. Remove the integration relay from the engine room relay block and junction block assembly.

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

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      3C-2 - D20-2 (+B) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      3C-2 - D20-2 (+B) - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reinstall the integration relay.


    NG

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

    OK

  24. CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY - EFI MAIN RELAY)


    1. Remove the integration relay from the engine room relay block and junction block assembly.

    2. Remove the EFI MAIN relay from the engine room relay block and junction block assembly.

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

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      3C-7 - 3 (EFI MAIN relay terminal) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      3C-7 - 3 (EFI MAIN relay terminal) - Body ground Always 10 kΩ or higher

    4. Reinstall the integration relay.

    5. Reinstall the EFI MAIN relay.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (INTEGRATION RELAY - EFI MAIN RELAY)

    OK

    REPAIR OR REPLACE HARNESS OR CONNECTOR (INTEGRATION RELAY - BODY GROUND)