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SFI SYSTEM, Diagnostic DTC:P0171, P0172, P0174, P0175

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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)
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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)

  • 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, 2 sensor 1) circuit

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

  • A/F relay

  • A/F fuse

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

  • PCV valve and hose

  • PCV hose connections

  • Wire harness or connector

  • ECM

P0172

P0175

 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, 2 sensor 1) circuit

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

  • A/F relay

  • A/F fuse

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

  • Wire harness or connector

  • ECM
Tip:

  • 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.

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MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause 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 values. Deviations from the ECM's estimated fuel injection volumes also affect 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 the malfunction thresholds, the ECM interprets this as a fault in the fuel system and sets a DTC.


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WIRING DIAGRAM

Refer to DTC P0100 (Click here)

Refer to DTC P2195 (Click here).

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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 (even if no DTCs are stored, perform the clear DTC procedure).

  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 120 km/h (37 and 74 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.

    Tip:

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

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INSPECTION PROCEDURE

Tip:

Intelligent tester only:

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F 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. Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.

  5. Perform the Active Test 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 Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.

    Tip:

    • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.

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

    Tester Display (Sensor) Injection Volume Status Voltage

    AFS Voltage B1S1 or AFS Voltage B2S1

    (Air fuel ratio)

    		 12.5% Rich Less than 3.1

    AFS Voltage B1S1 or AFS Voltage B2S1

    (Air fuel ratio)

    		 -12.5% Lean More than 3.4

    O2S B1S2 or O2S B2S2

    (Heated oxygen)

    		 12.5% 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 A01CFAQE13 A01CBBDE08 A01CFAQE13 A01CET8E06 -
    2 A01CFAQE13 A01CBU2E01 A01CFAQE13 A01CET8E06

    • Air fuel ratio sensor

    • Air fuel ratio sensor heater

    • Air fuel ratio sensor circuit
    3 A01CFAQE13 A01CBBDE08 A01CFAQE13 A01CBU2E01

    • Heated oxygen sensor

    • Heated oxygen sensor heater

    • Heated oxygen sensor circuit

    • Exhaust gas leaks
    4 A01CFAQE13 A01CBU2E01 A01CFAQE13 A01CBU2E01

    • Fuel pressure

    • Exhaust gas leaks

      (Air fuel ratio extremely lean or rich)

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

    • To display the graph, enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor / AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2.

Note:

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

Tip:

  • 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.

  • Bank 1 refers to the bank that includes cylinder No. 1.

  • Bank 2 refers to the bank that does not include cylinder No. 1.

  • Sensor 1 refers to the sensor closest to the engine assembly.

  • Sensor 2 refers to the sensor farthest away from the engine assembly.

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PROCEDURE


  1. Click here

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

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

    4. Read the DTCs.

      Result
      Result Proceed to
      DTC P0171, P0172, P0174 and/or P0175 are output A
      DTC P0171, P0172, P0174 or P0175 and other DTCs are output B
      Tip:

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


  2. Click here

    CHECK PCV HOSE (HOSE CONNECTIONS)


    1. Check the PCV hose connections (Click here).

      OK
      PCV hose is connected correctly and is not damaged.

  3. Click here

    CHECK INTAKE SYSTEM


    1. Check the intake system for vacuum leaks (Click here).

      OK
      No leaks in intake system.

  4. Click here

    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. Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.

    5. Perform the Active Test operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).

    6. 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 tester.

      Tip:

      • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.

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

      • If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

      Tester Display (Sensor) Injection Volume Status Voltage

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio)

      		 12.5% Rich Less than 3.1 V

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio)

      		 -12.5% Lean More than 3.4 V

      O2S B1S2 or O2S B2S2

      (Heated oxygen)

      		 12.5% Rich More than 0.55 V

      O2S B1S2 or O2S B2S2

      (Heated oxygen)

      		 -12.5% Lean Less than 0.4 V
      Result
      Status AFS B1S1 or AFS B2S1 Status 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 assembly blockage

      • Gas leaks 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 leakage or blockage

      • Gas leaks from exhaust system

      • Ignition system

      • Fuel pressure

      • Mass air flow meter sub-assembly

      • 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) is consistently more than 3.35 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.

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


  5. Click here

    READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

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

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

    4. Read the Data List twice, when the engine is both cold and warmed up.

      Standard
      Tester Display Condition Specified Condition
      Coolant Temp Cold engine Same as ambient air temperature
      Warm engine Between 80 and 100°C (176 and 212°F)

  6. Click here

    READ VALUE USING INTELLIGENT TESTER (MAF)


    1. Connect the intelligent tester to the DLC3.

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

    3. Enter the following menus: Powertrain / Engine / Data List / MAF, Coolant Temp and Engine Speed.

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

    5. Read MAF with the engine speed at 2500 rpm.

      Standard
      Tester Display Condition Specified Condition
      MAF

      Shift lever position: N

      A/C: Off

      Engine Speed: 2500 rpm

      		 Between 8 gm/s and 19 gm/s

  7. Click here

    CHECK FUEL PRESSURE


    1. Check the fuel pressure (Click here).


  8. Click here

    INSPECT FOR EXHAUST GAS LEAK


    1. Inspect for exhaust gas leak from the exhaust manifold sub-assembly and exhaust pipes.

      OK
      No gas leaks

  9. Click here

    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.

  10. Click here

    INSPECT FUEL INJECTOR ASSEMBLY (INJECTION VOLUME)


    1. Inspect the fuel injector assembly (Click here).


  11. Click here

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. Inspect the air fuel ratio sensor (Click here).


  12. Click here

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


    1. A01CFINE01

      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 Switch Condition Specified Condition
      D27-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V
      D7-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


  13. Click here

    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
      D27-1 (HA1A) - D1-86 (HA1A) Always Below 1 Ω
      D27-3 (A1A+) - D1-93 (A1A+) Always Below 1 Ω
      D27-4 (A1A-) - D1-116 (A1A-) Always Below 1 Ω
      D7-1 (HA2A) - D1-109 (HA2A) Always Below 1 Ω
      D7-3 (A2A+) - D1-120 (A2A+) Always Below 1 Ω
      D7-4 (A2A-) - D1-119 (A2A-) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      D27-1 (HA1A) or D1-86 (HA1A) - Body ground Always 10 kΩ or higher
      D27-3 (A1A+) or D1-93 (A1A+) - Body ground Always 10 kΩ or higher
      D27-4 (A1A-) or D1-116 (A1A-) - Body ground Always 10 kΩ or higher
      D7-1 (HA2A) or D1-109 (HA2A) - Body ground Always 10 kΩ or higher
      D7-3 (A2A+) or D1-120 (A2A+) - Body ground Always 10 kΩ or higher
      D7-4 (A2A-) or D1-119 (A2A-) - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reconnect the ECM connector.


  14. Click here

    REPLACE AIR FUEL RATIO SENSOR


    1. Replace the air fuel ratio sensor (Click here).


  15. Click here

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


    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 and wait for at least 30 seconds.

    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 Confirmation Driving Pattern.

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

    9. Read the DTCs.

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

  16. Click here

    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).

      Tip:

      Repair any problems.


  17. Click here

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


    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 and wait for at least 30 seconds.

    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 Confirmation Driving Pattern.

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

    9. Read the DTCs.

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

  18. Click here

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


    1. A01CD9ZE01

      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
      D2-5 (VG) - D1-72 (VG) Always Below 1 Ω
      D2-4 (E2G) - D1-73 (E2G) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      D2-5 (VG) or D1-72 (VG) - Body ground Always 10 kΩ or higher

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

    5. Reconnect the ECM connector.


  19. Click here

    REPLACE MASS AIR FLOW METER SUB-ASSEMBLY


    1. Replace the mass air flow meter sub-assembly (Click here).

      Tip:

      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.


  20. Click here

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


    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 and wait for at least 30 seconds.

    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 Confirmation Driving Pattern.

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

    9. Read the DTCs.

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

  21. Click here

    CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - A/F RELAY)


    1. Disconnect the air fuel ratio sensor connector.

    2. Remove the A/F relay from the engine room 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
      D27-2 (+B) - A/F relay (3) Always Below 1 Ω
      D7-2 (+B) - A/F relay (3) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      D27-2 (+B) or A/F relay (3) - Body ground Always 10 kΩ or higher
      D7-2 (+B) or A/F relay (3) - Body ground Always 10 kΩ or higher

    4. Reinstall the A/F relay.

    5. Reconnect the air fuel ratio sensor connector.


  22. Click here

    INSPECT A/F RELAY


    1. Inspect the A/F relay (Click here).


  23. Click here

    CHECK HARNESS AND CONNECTOR (A/F RELAY - BODY GROUND)


    1. A01CCH2E01

      Remove the A/F relay from the engine room relay block.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      A/F relay (2) - Body ground Always Below 1 Ω

    3. Reinstall the A/F relay.


  24. Click here

    CHECK HARNESS AND CONNECTOR (A/F RELAY POWER SOURCE)


    1. A01CCH2E01

      Remove the A/F relay from the engine room relay block.

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

      Standard Voltage
      Tester Connection Condition Specified Condition
      A/F relay (5) - Body ground Always 11 to 14 V

    3. Reinstall the A/F relay.


  25. Click here

    GO TO DTC CHARTClick here

  26. Click here

    REPAIR OR REPLACE PCV HOSE

  27. Click here

    REPAIR OR REPLACE INTAKE SYSTEM

  28. Click here

    REPLACE ENGINE COOLANT TEMPERATURE SENSORClick here

  29. Click here

    REPAIR OR REPLACE HARNESS AND CONNECTOR

  30. Click here

    REPAIR OR REPLACE FUEL SYSTEM

  31. Click here

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

  32. Click here

    REPAIR OR REPLACE IGNITION SYSTEM

  33. Click here

    REPLACE FUEL INJECTOR ASSEMBLYClick here

  34. Click here

    REPLACE AIR FUEL RATIO SENSORClick here

  35. Click here

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

  36. Click here

    REPLACE ECMClick here

  37. Click here

    END

  38. Click here

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

  39. Click here

    REPLACE A/F RELAY

  40. Click here

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - BODY GROUND)

  41. Click here

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - EFI MAIN RELAY)

  42. Click here

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - BATTERY)