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 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 three-way catalytic converter, the ECM calculates the oxygen storage capacity of the three-way catalytic converter. 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 three-way catalytic converter. 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 three-way catalytic converter.

The ECM uses the oxygen storage capacity value to determine the state of the three-way catalytic converter. 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 (sensor 1)

  • Heated oxygen sensor (sensor 2)

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

  • EGR valve assembly

CATALYST LOCATION

A003SJGE01
Text in Illustration
*A w/ Exhaust Heat Recirculation System *B w/o Exhaust Heat Recirculation System
*1 Exhaust Manifold Sub-assembly *2 Front Exhaust Pipe Assembly (TWC: Front and Rear Catalyst)
*3 Tail Exhaust Pipe Assembly *4 Air Fuel Ratio Sensor (Sensor 1)
*5 Heated Oxygen Sensor (Sensor 2) - -

CONFIRMATION DRIVING PATTERN

Tech Tips

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

A003TIVE07

  1. Connect the intelligent tester to the DLC3.

  2. Turn the power switch on (IG).

  3. Turn the tester on.

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

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

  6. Turn the power switch on (IG) and turn the tester on.

  7. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Catalyst Monitor.

  8. Check that Catalyst Monitor is Incmpl (Incomplete).

  9. Put the engine in inspection mode Click here.

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

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

    CAUTION:

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

    Tech Tips


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

    • The monitor item will change to Compl (Complete) after completing the driving pattern [C].

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

  13. Check if any DTCs (pending DTCs) are stored.

    Tech Tips

    If the monitor does not change to Compl (Complete), and no pending DTCs are stored, perform the following procedure.

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

    CAUTION:

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

    Tech Tips


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

    • The monitor item will change to Compl (Complete) after completing the driving pattern [E].

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

  16. Check if any DTCs (pending DTCs) are stored.

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.

A003T7GE57

  • (a) Connect the intelligent tester to the DLC3 [A].

  • (b) Turn the power switch on (IG) and turn the tester on [B].

  • (c) Put the engine in inspection mode Click here [C].

  • (d) Start the engine and warm it up with all the accessories switched off until the engine coolant temperature stabilizes [D].

  • (e) Run the engine at an engine speed of between 1500 rpm and 2500 rpm for at least 3 minutes [E].

  • (f) While running the engine at 2500 rpm for 2 seconds and then 1500 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the tester [F].

Tech Tips


  • If either of the voltage outputs of the air fuel ratio or heated oxygen sensor does not fluctuate, or there is noise in the waveform of either sensor, 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, perform the Active Test operation by entering the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

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

A003T4CE39

INSPECTION PROCEDURE


  1. AIR FUEL RATIO CONTROL

    Tech Tips

    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. Turn the power switch on (IG) and turn the tester on.

    3. Put the engine in inspection mode Click here.

    4. Start the engine.

    5. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

    6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.

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

    8. Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (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 12.5% or increases the injection volume by 25%.

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

      Tester Display (Sensor) Injection Volume Status Voltage

      AFS Voltage B1S1

      (Air fuel ratio)

      		 +25% Rich Less than 3.1 V

      AFS Voltage B1S1

      (Air fuel ratio)

      		 -12.5% Lean More than 3.4 V

      O2S B1S2

      (Heated oxygen)

      		 +25% Rich More than 0.55 V

      O2S B1S2

      (Heated oxygen)

      		 -12.5% 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.

      Case

      Air Fuel Ratio Sensor (Sensor 1)

      Output Voltage

      Heated Oxygen Sensor (Sensor 2)

      Output Voltage

      		 Main Suspected Trouble Area
      1 A003UKNE12 A003UPYE01 -
      2 A003S3KE06 A003UPYE01

      • Air fuel ratio sensor

      • Air fuel ratio sensor heater

      • Air fuel ratio sensor circuit
      3 A003UKNE12 A003S3KE07

      • Heated oxygen sensor

      • Heated oxygen sensor heater

      • Heated oxygen sensor circuit

      • Exhaust gas leaks
      4 A003S3KE06 A003S3KE06

      • 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 and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.

      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.

      • 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 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 power switch on (IG).

    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

    GO TO DTC CHART Click here

    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. Turn the power switch on (IG) and turn the tester on.

    3. Put the engine in inspection mode Click here.

    4. Start the engine and warm it up.

    5. Run the engine at an engine speed of 2500 rpm for approximately 90 seconds.

    6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.

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

    8. 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 12.5% or increases the injection volume by 25%.

      • 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.

        Standard

        Tester Display

        (Sensor)

        		 Injection Volume Status Voltage

        AFS Voltage B1S1

        (Air fuel ratio)

        		 +25% Rich Less than 3.1 V
        -12.5% Lean More than 3.4 V

        O2S B1S2

        (Heated oxygen)

        		 +25% Rich More than 0.55 V
        -12.5% Lean Less than 0.4 V
        Result

        Status

        AFS Voltage B1S1

        Status

        O2S B1S2

        Air Fuel Ratio Condition and Air Fuel Ratio and

        Heated Oxygen Sensors Condition

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

        • Three-way catalytic converter

        • Gas leaks from exhaust system

        • EGR valve assembly

        		 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

        • EGR valve assembly

        		 D
        Rich Rich Actual air fuel ratio rich -

        • Extremely rich or lean actual air fuel ratio

        • Gas leaks from exhaust system

        • EGR valve assembly

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

        Rich: During the AFS Voltage is consistently less than 3.1 V, and the O2S 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

      Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2] Click here.


    B

    REPLACE AIR FUEL RATIO SENSOR (SENSOR 1) Click here

    C

    INSPECT FOR EXHAUST GAS LEAK Click here

    D

    INSPECT FOR EXHAUST GAS LEAK Click here

    A

  3. INSPECT FOR EXHAUST GAS LEAK


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

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

    4. Put the engine in inspection mode (maintenance mode) Click here.

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

      Tech Tips

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

    6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / All Data / Throttle Idle Position and MAP.

    7. Confirm that the Throttle Idle Position is ON and check the MAP value in the Data List while performing the Active Test.

      Note


      • 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.

      • Do not open the EGR valve 30 steps or more during the Active Test.

      OK
      MAP change in response to EGR step position when Throttle Idle Position is ON in Data List.
      Standard
      - EGR Step Position (Active Test)
      0 Steps 0 to 30 Steps

      MAP

      (Data List)

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

      Tech Tips


      • While performing the Active Test, if the increase in the value of MAP is small, the EGR valve assembly may be a malfunctioning.

      • Even if the EGR valve assembly is malfunctioning, rough idling or an increase in the value of MAP may occur while performing the Active Test. However, the amount that the value of MAP increases will be smaller than normal.

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

    B

    REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST) Click here

    A

  5. INSPECT EGR VALVE ASSEMBLY


    1. Remove the EGR valve assembly Click here.

    2. Check if the EGR valve is stuck open.

      OK
      EGR valve is tightly closed.

    3. Reinstall the EGR valve assembly Click here.


    NG

    REPLACE EGR VALVE ASSEMBLY Click here

    OK

    REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST) Click here

  6. INSPECT FOR EXHAUST GAS LEAK


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

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

    REPLACE HEATED OXYGEN SENSOR (SENSOR 2) Click here

  7. INSPECT FOR EXHAUST GAS LEAK


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

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

    4. Put the engine in inspection mode (maintenance mode) Click here.

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

      Tech Tips

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

    6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / All Data / Throttle Idle Position and MAP.

    7. Confirm that the Throttle Idle Position is ON and check the MAP value in the Data List while performing the Active Test.

      Note


      • 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.

      • Do not open the EGR valve 30 steps or more during the Active Test.

      OK
      MAP change in response to EGR step position when Throttle Idle Position is ON in Data List.
      Standard
      - EGR Step Position (Active Test)
      0 Steps 0 to 30 Steps

      MAP

      (Data List)

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

      Tech Tips


      • While performing the Active Test, if the increase in the value of MAP is small, the EGR valve assembly may be a malfunctioning.

      • Even if the EGR valve assembly is malfunctioning, rough idling or an increase in the value of MAP may occur while performing the Active Test. However, the amount that the value of MAP increases will be smaller than normal.

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

    B

    CHECK ENGINE TO DETERMINE CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO Click here

    A

  9. INSPECT EGR VALVE ASSEMBLY


    1. Remove the EGR valve assembly Click here.

    2. Check if the EGR valve is stuck open.

      OK
      EGR valve is tightly closed.

    3. Reinstall the EGR valve assembly Click here.


    NG

    REPLACE EGR VALVE ASSEMBLY Click here

    OK

    CHECK ENGINE TO DETERMINE CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO Click here