SFI SYSTEM, Diagnostic DTC:P0420

DTC Code DTC Name
P0420 Catalyst System Efficiency Below Threshold (Bank 1)

MONITOR DESCRIPTION

The ECM uses sensors mounted in front of and behind the three-way catalytic converter (TWC) to monitor its efficiency.

The first sensor, the air fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.

In order to detect any deterioration in the TWC, the ECM calculates the oxygen storage capacity of the TWC. This calculation is based on the voltage output of the heated oxygen sensor while performing active air fuel ratio control.

The oxygen storage capacity value is an indication of the oxygen storage capacity of the TWC. When the vehicle is being driven with a warm engine, active air fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air fuel ratio to lean or rich levels. If the cycle of the waveform for the heated oxygen sensor is long, the oxygen storage capacity is great. There is a direct correlation between the heated oxygen sensor and the oxygen storage capacity of the TWC.

The ECM uses the oxygen storage capacity value to determine the state of the TWC. If any deterioration has occurred, it illuminates the MIL and sets the DTC.

DTC No. DTC Detection Condition Trouble Area
P0420

Oxygen storage capacity value smaller than standard value under active air fuel ratio control

(2 trip detection logic)


  • Gas leaks from exhaust system

  • Air fuel ratio sensor (bank 1 sensor 1)

  • Heated oxygen sensor (bank 1 sensor 2)

  • Exhaust manifold assembly

  • Front exhaust pipe assembly (TWC: front and rear catalyst)

  • EGR valve assembly

Tech Tips


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

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

CATALYST LOCATION

A005I0QE01
Text in Illustration
*1 Exhaust Manifold Assembly *2 Air Fuel Ratio Sensor (Bank 1 Sensor 1)
*3 Heated Oxygen Sensor (Bank 1 Sensor 2) *4 Front Exhaust Pipe Assembly (TWC: Front and Rear Catalyst)
*5 Tail Exhaust Pipe Assembly - -

CONFIRMATION DRIVING PATTERN

Tech Tips

Performing this confirmation driving pattern will activate the catalyst monitor. This is very useful for verifying the completion of a repair.

A005IU1E01

  1. Connect the intelligent tester to the DLC3.

  2. Turn the ignition switch to ON.

  3. Turn the tester on.

  4. Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).

  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.

  7. Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher [A].

  8. Drive the vehicle at approximately 60 km/h (37 mph) for 10 minutes or more [B].

    Tech Tips

    Drive the vehicle while keeping the engine load as constant as possible.

    CAUTION:

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

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

  10. 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.

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

  12. Input the DTC: P0420.

  13. Check the DTC judgment result.

    Tester Display Description
    NORMAL
    • DTC judgment completed

    • System normal

    ABNORMAL
    • DTC judgment completed

    • System abnormal

    INCOMPLETE
    • DTC judgment not completed

    • 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 memory limit

    Tech Tips


    • If the judgment result shows NORMAL, the system is normal.

    • If the judgment result shows ABNORMAL, the system has a malfunction.

    • If the judgment result shows INCOMPLETE or UNKNOWN, perform steps [D] through [E].

  14. Drive the vehicle at a speed between 75 and 100 km/h (47 and 63 mph) for 10 minutes or more [D].

    Tech Tips

    Drive the vehicle while keeping the engine load as constant as possible.

    CAUTION:

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

  15. Check the DTC judgment result again [E].

CONDITIONING FOR SENSOR TESTING

Tech Tips

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the air fuel ratio sensor and heated oxygen sensor. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.

A005HKCE02

  • (a) Connect the intelligent tester to the DLC3 (Step "A").

  • (b) Start the engine and warm it up with all the accessories switched off, until the engine coolant temperature stabilizes (Step "B").

  • (c) Run the engine at an engine speed of between 2500 rpm and 3000 rpm for at least 3 minutes (Step "C").

  • (d) While running the engine at 3000 rpm for 2 seconds and 2000 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the tester (Step "D").

Tech Tips


  • If either of the voltage outputs of the air fuel ratio or heated oxygen sensors does not fluctuate, or either of the sensors has noise in its output, the sensor may be malfunctioning.

  • If the voltage outputs of both the sensors remain lean or rich, the air fuel ratio may be extremely lean or rich. In such cases, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

  • If the TWC has deteriorated, the heated oxygen sensor (located behind the TWC) voltage output fluctuates up and down frequently, even under normal driving conditions (active air fuel ratio control is not performed).

A005JBRE03

CAUTION / NOTICE / HINT

Tech Tips


  • After performing repairs, drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern and check if DTC P0420 is output again. If a DTC is output again, replace the catalyst if it has not been replaced already.

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

PROCEDURE


  1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420)


    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 P0420 is output A
      DTC P0420 and other DTCs are output B

      Tech Tips

      If any DTCs other than P0420 are output, troubleshoot those DTCs first.


    B
    A
  2. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine and warm it up.

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

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

      Tech Tips


      • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by -12% or increases the injection volume by +12%.

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

        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

        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 and

        Heated Oxygen Sensor Condition

        Misfire Main Suspected Trouble Area Proceed to
        Lean/Rich Lean/Rich Normal -
        • TWC

        • Gas leaks from exhaust system

        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

        Lean/Rich Lean Heated oxygen sensor malfunction -
        • Heated oxygen sensor

        • Gas leaks from exhaust system

        C
        Lean/Rich Rich Heated oxygen sensor malfunction -
        • Heated oxygen sensor

        • Gas leaks from exhaust system

        Lean Lean Actual air fuel ratio lean May occur
        • Extremely rich or lean actual air fuel ratio

        • Gas leaks from exhaust system

        D
        Rich Rich Actual air fuel ratio rich -
        • Extremely rich or lean actual air fuel ratio

        • Gas leaks from exhaust system

        Lean: During Control the Injection Volume for A/F Sensor, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently less than 0.4 V.

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

      Tech Tips

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


    B
    C
    D
    A
  3. INSPECT FOR EXHAUST GAS LEAK


    1. Inspect for exhaust gas leaks from the exhaust manifold assembly and exhaust pipes.

      OK
      No gas leaks.

    NG
    OK
  4. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)


    1. Check the EGR valve assembly operation.


      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. Check the engine idling condition in the Data List while performing the Active Test.

        OK

        EGR Step Position

        (Active Test)

        Specified Condition
        0 Steps Steady idling
        0 to 30 Steps Idling changes from steady to rough idling

        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.

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

    B
    A
  5. INSPECT EGR VALVE ASSEMBLY


    1. Remove the EGR valve assembly Click here.

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

      OK
      EGR valve is not contaminated with foreign objects.
    3. Reinstall the EGR valve assembly Click here.


    OK
    NG
  6. INSPECT FOR EXHAUST GAS LEAK


    1. Inspect for exhaust gas leaks from the exhaust assembly and exhaust pipes.

      OK
      No gas leaks.

    OK
    NG
  7. INSPECT FOR EXHAUST GAS LEAK


    1. Inspect for exhaust gas leaks from the exhaust assembly and exhaust pipes.

      OK
      No gas leaks.

    NG
    OK
  8. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)


    1. Check the EGR valve assembly operation.


      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. Check the engine idling condition in the Data List while performing the Active Test.

        OK

        EGR Step Position

        (Active Test)

        Specified Condition
        0 Steps Steady idling
        0 to 30 Steps Idling changes from steady to rough idling

        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.

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

    B
    A
  9. INSPECT EGR VALVE ASSEMBLY


    1. Remove the EGR valve assembly Click here.

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

      OK
      EGR valve is not contaminated with foreign objects.
    3. Reinstall the EGR valve assembly Click here.


    OK
    NG