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 the 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.

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

  • 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

  • EGR valve assembly

  • 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

  • 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)

  • EGR valve assembly

  • 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 more than +40% or less than -40%, the ECM interprets this as a fuel system malfunction.

A005I5SE02

CONFIRMATION DRIVING PATTERN

A005MDYE79

  1. Connect the intelligent tester to the DLC3.

  2. Turn the ignition switch to ON.

  3. Turn the tester on.

  4. Clear the DTCs Click here.

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

  6. Turn the ignition switch to ON and turn the tester on. [A]

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

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

  9. Drive the vehicle at between 60 and 100 km/h (37 and 63 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes. [D]

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

  11. Read the pending DTCs.

    Tech Tips


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

    • If a pending DTC is not output, perform the following procedure.

  12. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

  13. Input the DTC: P0171 or P0172.

  14. Check the DTC judgment result.

    Intelligent Tester
    Tester Display Description
    NORMAL

    • DTC judgment completed

    • System normal
    ABNORMAL

    • DTC judgment completed

    • System abnormal
    INCOMPLETE

    • DTC judgment not completed

    • You should perform driving pattern after confirming DTC enabling conditions
    UNKNOWN

    • Unable to perform DTC judgment

    • Number of DTCs which do not fulfill DTC preconditions has reached ECU's memory limit

    CAUTION:

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

    Tech Tips

    If the judgment result shows INCOMPLETE or UNKNOWN, perform steps [C] or [E] again.

WIRING DIAGRAM

Refer to DTC P0031 Click here.

Refer to DTC P0102 Click here.

CAUTION / NOTICE / HINT

Tech Tips


  • Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions 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.

  • 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 ignition switch to ON.

    3. Turn the tester on.

    4. Enter the following menus: Powertrain / Engine and ECT / 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 (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 and ECT / Active Test / Control the Injection Volume.

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

    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 -12.0% to +12.0%. The injection volume can be changed in fine gradations.

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

      • If the output voltage has almost no change, the air fuel ratio sensor may have a malfunction.

      Standard Voltage

      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.

      Result

      Status

      AFS Voltage B1S1

      Status

      O2S B1S2

      Air Fuel Ratio Condition and

      Air Fuel Ratio Sensor Condition

      		 Misfire Suspected Trouble Area Proceed to
      Lean/Rich Lean/Rich Normal - - A
      Lean Lean Actual air fuel ratio lean May occur

      • PCV valve and hose

      • PCV hose connections

      • Injector blockage

      • Gas leak from exhaust system

      • Intake system

      • Fuel pressure

      • Mass air flow meter

      • Manifold absolute pressure sensor

      • Engine coolant temperature sensor
      Rich Rich Actual air fuel ratio rich -

      • Injector blockage

      • Gas leak from exhaust system

      • Ignition system

      • Fuel pressure

      • Mass air flow meter

      • Manifold absolute pressure sensor

      • Engine coolant temperature sensor
      Lean Lean/Rich Air fuel ratio sensor malfunction -

      • Air fuel ratio sensor

      • EGR valve

      		 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) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S) 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 B1S1 is consistently more than 0.55 V.

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


    B

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

    A

  5. 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 value
      With cold engine:
      Same as ambient air temperature.
      With warm engine:
      75 to 100°C (167 to 212°F).

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  6. READ VALUE USING INTELLIGENT TESTER (MAF)


    1. Read the values using the intelligent tester (MAF).

    2. Connect the intelligent tester to the DLC3.

    3. Turn the ignition switch to ON.

    4. Turn the tester on.

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

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

    7. Read MAF with the engine speed 3000 rpm.

      Standard
      Between 5.4 gm/sec. and 9.6 gm/sec. (shift lever: Neutral position; A/C: off).

    NG

    CHECK HARNESS AND CONNECTOR 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 IGNITION SYSTEM


    1. Check the ignition system Click here.


    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION VOLUME)


    1. Inspect the fuel injector assembly Click here.

      Tech Tips

      Perform "Inspection After Repairs" after replacing the fuel injector assembly Click here.


    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)


    1. A005HVCE04
      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.

      Tech Tips

      Perform "Inspection After Repairs" after replacing the air fuel ratio sensor Click here.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

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


    1. A005M3YE02
      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 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
      B39-2 (+B) - Body ground Ignition switch ON 11 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


    NG

    CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY) 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)
      for RHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) - B23-23 (HA1A) Always Below 1 Ω
      for LHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) - B22-23 (HA1A) Always Below 1 Ω
      Standard Resistance (Check for Short)
      for RHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) or B23-23 (HA1A) - Body ground Always 10 kΩ or higher
      for LHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) or B22-23 (HA1A) - 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

    OK

  14. REPLACE AIR FUEL RATIO SENSOR


    1. Replace the air fuel ratio sensor Click here.

      Tech Tips

      Perform "Inspection After Repairs" after replacing the air fuel ratio sensor Click here.


    NEXT

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


    1. Perform the confirmation driving pattern.

      Tech Tips

      Refer to the Confirmation Driving Pattern.

      Result
      Result Proceed to
      ABNORMAL A
      NORMAL B

    B

    END

    A

  16. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

    4. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or more.

      Tech Tips

      The A/C switch and all accessory switches should be off.

    5. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

    6. Confirm that the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

      OK
      MAP and idling condition change in response to EGR step position.
      Standard
      - EGR Step Position (Active Test)
      0 Steps 0 to 30 Steps
      Idling condition Steady idling Idling changes from steady to rough idling

      MAP

      (Data List)

      MAP value is 28 to 48 kPa

      (210 to 360 mmHg)

      (EGR valve is fully closed)

      		 MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

      Tech Tips


      • Do not leave the EGR valve open for 10 seconds or more during the Active Test.

      • Be sure to return the EGR valve to step 0 when the Active Test is completed.

      • During Active Test, if the idling condition does not change in response to EGR step position, then there is probably a malfunction in the EGR valve.

      Result
      Result Proceed to
      Outside of standard range A
      Within standard range B

    B

    CHECK HARNESS AND CONNECTOR Click here

    A

  17. INSPECT EGR VALVE ASSEMBLY (VISUALLY CHECK EGR VALVE)


    1. Remove the EGR valve assembly Click here.

    2. Check for contamination between the EGR valve and housing.

      OK
      No leaks or blockage

    3. Reinstall the EGR valve assembly Click here.


    NG

    REPLACE EGR VALVE ASSEMBLY Click here

    OK

  18. CHECK HARNESS AND CONNECTOR


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

      Tech Tips

      Repair any problems.


    NEXT

  19. 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 the DTCs Click here.

    5. Turn the ignition switch off.

    6. Turn the ignition switch to ON 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 Confirmation Driving Pattern.

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

    10. Read DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 A

      No DTCs output

      (No pending DTCs output)

      		 B

    B

    END

    A

  20. 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 (Check for Open)
      for RHD
      Tester Connection Condition Specified Condition
      B73-5 (VG) - B23-91 (VG) Always Below 1 Ω
      B73-4 (E2G) - B23-92 (E2G) Always Below 1 Ω
      for LHD
      Tester Connection Condition Specified Condition
      B73-5 (VG) - B22-91 (VG) Always Below 1 Ω
      B73-4 (E2G) - B22-92 (E2G) Always Below 1 Ω
      Standard Resistance (Check for Short)
      for RHD
      Tester Connection Condition Specified Condition
      B73-5 (VG) or B23-91 (VG) - Body ground Always 10 kΩ or higher
      for LHD
      Tester Connection Condition Specified Condition
      B73-5 (VG) or B22-91 (VG) - Body ground Always 10 kΩ or higher

    4. Reconnect the mass air flow meter connector.

    5. Reconnect the ECM connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  21. 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.

      • Perform "Inspection After Repairs" after replacing the mass air flow meter Click here.


    NEXT

  22. CHECK WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

    4. Clear the DTCs Click here.

    5. Turn the ignition switch off.

    6. Turn the ignition switch to ON 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 Confirmation Driving Pattern.

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

    10. Read DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 A

      No DTCs output

      (No pending DTCs output)

      		 B

    A

    REPLACE ECM Click here

    B

    END

  23. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY)


    1. Disconnect the air fuel ratio sensor connector.

    2. Remove the No. 1 integration relay from the engine room main relay block.

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

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      B39-2 (+B) - 1E-4 Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      B39-2 (+B) or 1E-4 - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reinstall the No. 1 integration relay.


    OK

    CHECK ECM POWER SOURCE CIRCUIT Click here

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR