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Home >> Toyota >> 2021 >> Sequoia TRD Pro >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System (3UR-FE) - Diagnostic Codes (3 Of 9) >> SFI System >> DTC P0171: System Too Lean (Bank 1); DTC P0172: System Too Rich (Bank 1); DTC P0174: System Too Lean (Bank 2); DTC P0175: System Too Rich (Bank 2) [08/2015 - 08/2019] >> Procedure
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DTC P0171: System Too Lean (Bank 1); DTC P0172: System Too Rich (Bank 1); DTC P0174: System Too Lean (Bank 2); DTC P0175: System Too Rich (Bank 2) [08/2015 - 08/2019]: Procedure

  1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175) 
    1. Connect the Techstream to the DLC3.
    2. Turn the ignition switch to ON.
    3. Turn the Techstream on.
    4. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
    5. Read DTCs.
      RESULT

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

      HINT: 

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

    Result: 

    B 

    GO TO DTC CHART 

    Refer to:

    DIAGNOSTIC TROUBLE CODE CHART [08/2015 - 10/2016] , or refer to

    DIAGNOSTIC TROUBLE CODE CHART [10/2016 - 08/2018] , or refer to

    DIAGNOSTIC TROUBLE CODE CHART [08/2018 - 08/2019]

    Result: 

    A 

    See step  2

  2. CHECK PCV HOSE CONNECTIONS 
    1. Check the PCV hose connections (Refer to PROCEDURE - Step 2 ).

      OK

      PCV hose is connected correctly and is not damaged.

    Result: 

    NG 

    REPAIR OR REPLACE PCV HOSE 

    (Refer to REMOVAL [08/2015 - ] )

    Result: 

    OK 

    See step  3

  3. CHECK AIR INDUCTION SYSTEM 

    HINT: 

    If a malfunction occurs when depressing the brake pedal, inspect the brake booster assembly, as there may be a vacuum leak in the brake booster assembly itself.

    1. Check the air induction system for vacuum leakage (Refer to PROCEDURE - Step 4 ).

      OK

      No leakage from air induction system.

      HINT: 

      Perform "Inspection After Repair" after repairing or replacing the air induction system (Refer to INITIALIZATION [08/2015 - 08/2019] ).

    Result: 

    NG 

    REPAIR OR REPLACE AIR INDUCTION SYSTEM 

    Result: 

    OK 

    See step  4

  4. PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME FOR A/F SENSOR) 
    1. Connect the Techstream to the DLC3.
    2. Start the engine.
    3. Turn the Techstream on.
    4. Warm up the engine and 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 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 Techstream.

      HINT: 

      • 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.
      Techstream Display (Sensor) Injection Volume Status Voltage
      AFS Voltage B1S1 or AFS Voltage B2S1
      (Air fuel ratio)      		 +12.5% Rich Below 3.1 V
      -12.5% Lean Higher than 3.4 V
      O2S B1S2 or O2S B2S2
      (Heated oxygen)      		 +12.5% Rich Higher than 0.55 V
      -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 blockage
      • Gas leaks from exhaust system
      • Air induction system
      • Fuel pressure
      • Mass air flow meter
      • Engine coolant temperature sensor
      		 A
      Rich Rich Actual air fuel ratio rich
      • Fuel injector leaks 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, 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, 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 Active Test, the output voltage of the heated oxygen sensor alternates correctly.

    Result: 

    B 

    See step  11

    Result: 

    A 

    See step  5

  5. READ VALUE USING TECHSTREAM (COOLANT TEMP) 
    1. Connect the Techstream to the DLC3.
    2. Turn the ignition switch to ON.
    3. Turn the Techstream on.
    4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.
    5. 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 100°C (167°F and 212°F).

      HINT: 

      Perform "Inspection After Repair" after replacing the engine coolant temperature sensor (Refer to INITIALIZATION [08/2015 - 08/2019] ).

    Result: 

    NG 

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR 

    (Refer to REMOVAL [08/2015 - ] )

    Result: 

    OK 

    See step  6

  6. READ VALUE USING TECHSTREAM (MAF) 
    1. Connect the Techstream to the DLC3.
    2. Turn the ignition switch to ON.
    3. Turn the Techstream 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 the Coolant Temp reaches 75°C (167°F) or more.
    6. Read MAF with the engine speed at 3000 RPM.

      Standard

      Between 18.0 gm/sec and 27.0 gm/sec (shift lever: N; A/C: Off).

    Result: 

    NG 

    See step  16

    Result: 

    OK 

    See step  7

  7. CHECK FUEL PRESSURE 
    1. Check the fuel pressure (Refer to PROCEDURE - Step 2 ).

    Result: 

    NG 

    REPAIR OR REPLACE FUEL SYSTEM 

    Result: 

    OK 

    See step  8

  8. CHECK FOR EXHAUST GAS LEAK 
    1. Check for exhaust gas leak.

      OK

      No gas leakage.

      HINT: 

      Perform "Inspection After Repair" after repairing or replacing the exhaust system (Refer to INITIALIZATION [08/2015 - 08/2019] ).

    Result: 

    NG 

    REPAIR OR REPLACE EXHAUST SYSTEM 

    Result: 

    OK 

    See step  9

  9. CHECK FOR SPARKS AND IGNITION 

    See step  [08/2015 - 08/2017], or

    see step  [08/2017 - 08/2019]

    Result: 

    NEXT 

    See step  10

  10. INSPECT FUEL INJECTOR (INJECTION AND VOLUME) 
    1. Check the injection volume (Refer to INSPECTION [08/2015 - ] ).

      HINT: 

      Perform "Inspection After Repair" after replacing the fuel injector assembly (Refer to INITIALIZATION [08/2015 - 08/2019] ).

    Result: 

    OK 

    See step  15

    Result: 

    NG 

    REPLACE FUEL INJECTOR 

    (Refer to REMOVAL [08/2015 - ] )

  11. INSPECT AIR-FUEL RATIO SENSOR (HEATER RESISTANCE) 

    Refer to:

    PROCEDURE - Step 1 [08/2015 - 10/2016] , or refer to

    PROCEDURE - Step 1 [10/2016 - 08/2017] , or refer to

    PROCEDURE - Step 1 [08/2017 - 08/2019]

    Result: 

    NG 

    REPLACE AIR FUEL RATIO SENSOR 

    (Refer to REMOVAL [08/2015 - ] )

    Result: 

    OK 

    See step  12

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

    Refer to

    PROCEDURE - Step 2 [08/2015 - 10/2016] , or refer to

    PROCEDURE - Step 2 [10/2016 - 08/2017] , or refer to

    PROCEDURE - Step 2 [08/2017 - 08/2019]

    Result: 

    NG 

    See step  21

    Result: 

    OK 

    See step  13

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

    Refer to

    PROCEDURE - Step 5 [08/2015 - 10/2016] , or refer to

    PROCEDURE - Step 5 [10/2016 - 08/2017] , or refer to

    PROCEDURE - Step 5 [08/2017 - 08/2019]

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  14

  14. REPLACE AIR FUEL RATIO SENSOR 
    1. Replace the air fuel ratio sensor (Refer to REMOVAL [08/2015 - ] ).

      HINT: 

      Perform "Inspection After Repair" after repairing or replacing the air fuel ratio sensor (Refer to INITIALIZATION [08/2015 - 08/2019] ).

    Result: 

    NEXT 

    See step  15

  15. PERFORM CONFIRMATION DRIVING PATTERN 
    1. Connect the Techstream to the DLC3.
    2. Turn the ignition switch to ON.
    3. Turn the Techstream on.
    4. Clear DTCs (Refer to DTC CHECK / CLEAR [08/2015 - 08/2019] ).
    5. Turn the ignition switch off and wait for at least 30 seconds.
    6. Turn the ignition switch to ON and turn the Techstream 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. Input the DTC: P0171, P0172, P0174 or P0175.
    11. Read DTCs.
      RESULT

      Result Proceed to
      ABNORMAL (DTC P0171, P0172, P0174 or P0175 is output) A
      NORMAL (No DTC is output) B

    Result: 

    B 

    END 

    Result: 

    A 

    See step  16

  16. 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 (Refer to ELECTRONIC CIRCUIT INSPECTION PROCEDURE [08/2015 - 08/2019] ).

      HINT: 

      Repair any problems.

    Result: 

    NEXT 

    See step  17

  17. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175) 
    1. Connect the Techstream to the DLC3.
    2. Turn the ignition switch to ON.
    3. Turn the Techstream on.
    4. Clear the DTCs (Refer to DTC CHECK / CLEAR [08/2015 - 08/2019] ).
    5. Turn the ignition switch off and wait for at least 30 seconds.
    6. Turn the ignition switch to ON and turn the Techstream 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 DTCs.
      RESULT

      Result Proceed to
      DTC P0171, P0172, P0174 or P0175 is output A
      DTC is not output B

    Result: 

    B 

    END 

    Result: 

    A 

    See step  18

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

    Refer to

    PROCEDURE - Step 3 [08/2015 - 08/2017] , or refer to

    PROCEDURE - Step 6 [08/2017 - 08/2019]

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  19

  19. REPLACE MASS AIR FLOW METER 
    1. Replace the mass air flow meter (Refer to REMOVAL [08/2015 - ] ).

      HINT: 

      • 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 Repair" after replacing the mass air flow meter (Refer to INITIALIZATION [08/2015 - 08/2019] ).

    Result: 

    NEXT 

    See step  20

  20. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED 
    1. Connect the Techstream to the DLC3.
    2. Turn the ignition switch to ON.
    3. Turn the Techstream on.
    4. Clear the DTCs (Refer to DTC CHECK / CLEAR [08/2015 - 08/2019] ).
    5. Turn the ignition switch off and wait for at least 30 seconds.
    6. Turn the ignition switch to ON and turn the Techstream 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 DTCs.
      RESULT

      Result  Proceed to
      DTC is not output A
      DTC P0171, P0172, P0174 or P0175 is output B

    Result: 

    A 

    END 

    Result: 

    B 

    REPLACE ECM 

    (Refer to REMOVAL [08/2015 - ] )

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

    Refer to

    PROCEDURE - Step 4 [08/2015 - 10/2016] , or refer to

    PROCEDURE - Step 4 [10/2016 - 08/2017] , or refer to

    PROCEDURE - Step 4 [08/2017 - 08/2019]

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  22

  22. INSPECT INTEGRATION RELAY (A/F) 
    1. Inspect the integration relay (A/F) (Refer to PROCEDURE - Step 3 ).

    Result: 

    OK 

    CHECK ECM POWER SOURCE CIRCUIT 

    Refer to

    ECM Power Source Circuit [08/2015 - 08/2017] , or refer to

    ECM Power Source Circuit [08/2017 - 08/2019]

    Result: 

    NG 

    REPLACE INTEGRATION RELAY 

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