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Home >> Toyota >> 2021 >> Land Cruiser Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Diagnostic Codes (2 Of 7) >> 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) [08/2018 - 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) [08/2018 - 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 engine switch on (IG) and turn the Techstream on.
    3. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
    4. 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 [08/2018 - 08/2019] )

    Result: 

    A 

    See step  2

  2. CHECK PCV HOSE CONNECTIONS 
    1. Check the PCV hose connections.

      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 leaks.

      OK

      No leaks from air induction system.

      HINT: 

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

    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. 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 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
      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 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 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.

    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 engine switch on (IG) and turn the Techstream on.
    3. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / 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 100°C (167°F and 212°F).

      HINT: 

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

    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 engine switch on (IG).
    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 Coolant Temp reaches 75°C (167°F) or higher.
    6. Read MAF with the engine speed at 3000 rpm.

      Standard

      Between 25.2 gm/sec and 35.2 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 leaks.

      OK

      No gas leaks.

      HINT: 

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

    Result: 

    NG 

    REPAIR OR REPLACE EXHAUST SYSTEM 

    Result: 

    OK 

    See step  9

  9. CHECK FOR SPARKS AND IGNITION 
    1. Perform a spark test (Refer to PROCEDURE - Step 1 ).

      HINT: 

      • If the result of the spark test is normal, proceed to the next step.
      • Perform "Inspection After Repair" after repairing or replacing the ignition system (Refer to INITIALIZATION [08/2015 - ] ).

    Result: 

    NEXT 

    See step  10

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

      HINT: 

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

    Result: 

    OK 

    See step  15

    Result: 

    NG 

    REPLACE FUEL INJECTOR ASSEMBLY 

    (Refer to REMOVAL [08/2015 - ] )

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) 
    1. Inspect the air fuel ratio sensor (Refer to INSPECTION [08/2015 - ] ).

      HINT: 

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

    Result: 

    NG 

    REPLACE AIR FUEL RATIO SENSOR 

    (Refer to REMOVAL [08/2015 - ] )

    Result: 

    OK 

    See step  12

  12. CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR) 
    GTY567333Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    1. Disconnect the A/F 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 Switch Condition Specified Condition
      C47-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V
      C48-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V

    Result: 

    NG 

    See step  21

    Result: 

    OK 

    See step  13

  13. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM) 
    1. Disconnect the A/F sensor connector.
    2. Disconnect the ECM connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      C47-1 (HA1A) - C53-22 (HA1A) Always Below 1 Ω
      C47-3 (A1A+) - C53-98 (A1A+) Always Below 1 Ω
      C47-4 (A1A-) - C53-97 (A1A-) Always Below 1 Ω
      C48-1 (HA2A) - C53-45 (HA2A) Always Below 1 Ω
      C48-3 (A2A+) - C53-121 (A2A+) Always Below 1 Ω
      C48-4 (A2A-) - C53-120 (A2A-) Always Below 1 Ω
      C47-1 (HA1A) or C53-22 (HA1A) - Body ground Always 10 kΩ or higher
      C47-3 (A1A+) or C53-98 (A1A+) - Body ground Always 10 kΩ or higher
      C47-4 (A1A-) or C53-97 (A1A-) - Body ground Always 10 kΩ or higher
      C48-1 (HA2A) or C53-45 (HA2A) - Body ground Always 10 kΩ or higher
      C48-3 (A2A+) or C53-121 (A2A+) - Body ground Always 10 kΩ or higher
      C48-4 (A2A-) or C53-120 (A2A-) - Body ground Always 10 kΩ or higher

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F SENSOR - ECM) 

    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 replacing the air fuel ratio sensor (Refer to INITIALIZATION [08/2015 - ] ).

    Result: 

    NEXT 

    See step  15

  15. PERFORM CONFIRMATION DRIVING PATTERN 
    1. Connect the Techstream to the DLC3.
    2. Turn the engine switch on (IG).
    3. Turn the Techstream on.
    4. Clear the DTCs (Refer to DTC CHECK / CLEAR [08/2015 - ] ).
    5. Turn the engine switch off.
    6. Turn the engine switch on (IG) 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 the Confirmation Driving Pattern.
    9. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
    10. Input the DTC: P0171, P0172, P0174 or P0175.
    11. Check the DTC judgment result.
      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.

      HINT: 

      Repair any problems.

    Result: 

    NEXT 

    See step  17

  17. CHECK WHETHER DTC OUTPUT RECURS 
    1. Connect the Techstream to the DLC3.
    2. Turn the engine switch on (IG).
    3. Turn the Techstream on.
    4. Clear the DTCs (Refer to DTC CHECK / CLEAR [08/2015 - ] ).
    5. Turn the engine switch off.
    6. Turn the engine switch on (IG) 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 (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

      Tester Connection Condition Specified Condition
      C3-3 (VG) - C53-68 (VG) Always Below 1 Ω
      C3-2 (E2G) - C53-70 (E2G) Always Below 1 Ω
      C3-3 (VG) or C53-68 (VG) - Body ground Always 10 kΩ or higher

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

    Result: 

    NEXT 

    See step  20

  20. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED 
    1. Connect the Techstream to the DLC3.
    2. Turn the engine switch on (IG).
    3. Turn the Techstream on.
    4. Clear the DTC (Refer to DTC CHECK / CLEAR [08/2015 - ] ).
    5. Turn the engine switch off.
    6. Turn the engine switch on (IG) 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 the 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 (NO. 2 INTEGRATION RELAY - A/F SENSOR) 
    1. Disconnect the A/F sensor connector.
    2. Remove the No. 2 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
      C47-2 (+B) - 1Q-3 Always Below 1 Ω
      C48-2 (+B) - 1Q-3 Always Below 1 Ω
      C47-2 (+B) or 1Q-3 - Body ground Always 10 kΩ or higher
      C48-2 (+B) or 1Q-3 - Body ground Always 10 kΩ or higher

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  22

  22. INSPECT NO. 2 INTEGRATION RELAY (A/F) 
    1. Inspect the No. 2 integration relay (Refer to ON-VEHICLE INSPECTION [08/2015 - ] ).

    Result: 

    OK 

    CHECK ECM POWER SOURCE CIRCUIT 

    (Refer to ECM Power Source Circuit [08/2015 - ] )

    Result: 

    NG 

    REPLACE NO. 2 INTEGRATION RELAY (A/F) 

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