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 (A/F) sensor, sends pre-catalyst information to the ECM. The second sensor, the Heated Oxygen (HO2) sensor, sends post-catalyst information to the ECM.

In order to detect any deterioration in the TWC, the ECM calculates the Oxygen Storage Capacity (OSC) of the TWC. This calculation is based on the voltage output of the HO2 sensor while performing active A/F control.

The OSC value is an indication of the OSC of the TWC. When the vehicle is being driven with a warm engine, active A/F control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the A/F to lean or rich levels. If the cycle of the waveform for the HO2 sensor is long, the OSC is great. There is a direct correlation between the HO2 sensor and the OSC of the TWC.

The ECM uses the OSC 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 converter sub-assembly (TWC: front catalyst)

  • Front exhaust pipe assembly (TWC: 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

A0117MRE01
Text in Illustration
*1 Air Fuel Ratio Sensor (Bank 1 Sensor 1) *2 Heated Oxygen Sensor (Bank 1 Sensor 2)
*3 Exhaust Manifold Converter Sub-Assembly (TWC: Front Catalyst) *4 Front Exhaust Pipe Assembly (TWC: Rear Catalyst)
*5 Tail Exhaust Pipe Assembly - -

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.

A0119NYE32

Tech Tips


  • (a) Connect the intelligent tester to the DLC3.

  • (b) Turn the ignition switch to ON.

  • (c) Turn the tester on.

  • (d) Clear the DTCs (if set) Click here.

  • (e) Turn the ignition switch off and wait for at least 30 seconds.

  • (f) Turn the ignition switch to ON and turn the tester on.

  • (g) Enter the following menus: Powertrain / Engine and ECT / Data List / Catalyst Monitor.

  • (h) Check that Catalyst Monitor is Incmpl (incomplete).

  • (i) Start the engine and warm it up [A].

  • (j) Drive the vehicle at between 64 km/h and 113 km/h (40 mph and 70 mph) for at least 10 minutes [B].

  • (k) The item will change to Compl (complete) after completing the drive pattern.

  • (l) Enter the following menus: Powertrain / Engine and ECT / DTC.

  • (m) Check if any DTCs (any pending DTCs) are set.

Note

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

Tech Tips

If Catalyst does not change to Compl (complete), and any pending DTCs fail to set, extend the driving time.

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.

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

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

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

A011B8GE03

INSPECTION PROCEDURE

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. 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 moving or stationary, 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.

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

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

      • 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)

        		 +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

        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 -

        • Exhaust manifold converter sub-assembly (TWC: front catalyst)

        • Front exhaust pipe assembly (TWC: rear catalyst)

        • EGR valve assembly

        • Gas leaks from exhaust system

        		 A
        Lean Lean/Rich Air fuel ratio sensor malfunction -

        • Air fuel ratio sensor (bank 1 sensor 1)

        		 B
        Rich Lean/Rich Air fuel ratio sensor malfunction -

        • Air fuel ratio sensor (bank 1 sensor 1)
        Lean/Rich Lean Heated oxygen sensor malfunction -

        • Heated oxygen sensor (bank 1 sensor 2)

        • Gas leaks from exhaust system

        		 C
        Lean/Rich Rich Heated oxygen sensor malfunction -

        • Heated oxygen sensor (bank 1 sensor 2)

        • Gas leaks from exhaust system
        Lean Lean Actual air fuel ratio lean May occur

        • Extremely rich or lean actual air fuel ratio

        • EGR valve assembly

        • Gas leaks from exhaust system

        		 D
        Rich Rich Actual air fuel ratio rich -

        • Extremely rich or lean actual air fuel ratio

        • EGR valve assembly

        • 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 air fuel ratio sensor or heated oxygen sensor alternates correctly.


    B

    REPLACE AIR FUEL RATIO SENSOR (BANK 1 SENSOR 1) Click here

    C

    CHECK FOR EXHAUST GAS LEAK Click here

    D

    CHECK FOR EXHAUST GAS LEAK Click here

    A

  3. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leaks from the exhaust manifold converter sub-assembly and exhaust pipe.

      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 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 MAP and Engine Speed in Date List at the idling condition while performing Active Test.

      OK
      MAP and idling condition change in response to EGR step position
      Standard
      - EGR Step Position (Active Test)
      0 Steps 0 to 30 Steps
      Idling condition Steady idling Idling changes from steady to rough idling

      MAP

      (Data List)

      MAP value is 20 to 40 kPa (150 to 300 mmHg)

      (EGR valve is fully closed)

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

      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 Active Test is completed.

      Result
      Result Proceed to
      NG A
      OK B

    B

    REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT 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 (It is not stuck open).

    3. Reinstall the EGR valve assembly Click here.


    NG

    REPLACE EGR VALVE ASSEMBLY Click here

    OK

  6. REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT CATALYST)


    1. Replace the exhaust manifold converter sub-assembly Click here.


    NEXT

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

  7. CHECK FOR EXHAUST GAS LEAK


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

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

    REPLACE HEATED OXYGEN SENSOR (BANK 1 SENSOR 2) Click here

  8. CHECK FOR EXHAUST GAS LEAK


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

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

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


    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 MAP and Engine Speed in Date List at the idling condition while performing Active Test.

      OK
      MAP and idling condition change in response to EGR step position
      Standard
      - EGR Step Position (Active Test)
      0 Steps 0 to 30 Steps
      Idling condition Steady idling Idling changes from steady to rough idling

      MAP

      (Data List)

      MAP value is 20 to 40 kPa (150 to 300 mmHg)

      (EGR valve is fully closed)

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

      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 Active Test is completed.

      Result
      Result Proceed to
      NG A
      OK B

    B

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

    A

  10. 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 (It is not stuck open).

    3. Reinstall the EGR valve assembly Click here.


    NG

    REPLACE EGR VALVE ASSEMBLY Click here

    OK

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