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 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 30 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, the ECM illuminates the MIL and stores the DTC.

This system determines the deterioration of the entire catalyst system (including the front and rear catalysts), by using the oxygen storage capacity value of the front catalyst, that is more sensitive than the rear catalyst, as the representative value. Therefore, be sure to replace the front and rear catalysts together when catalyst replacement is necessary.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

MIL

Memory

P0420

Catalyst System Efficiency Below Threshold (Bank 1)

The oxygen storage capacity value is less than the standard value under active air fuel ratio control (2 trip detection logic).

  • Gas leak from exhaust system

  • Air fuel ratio sensor (sensor 1)

  • Heated oxygen sensor (sensor 2)

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

Comes on

DTC stored

MONITOR STRATEGY

Required Sensors/Components (Main)

Air fuel ratio sensor

Heated oxygen sensor

Required Sensors/Components (Related)

Intake air temperature sensor

Mass air flow meter sub-assembly

Crankshaft position sensor

Engine coolant temperature sensor

Frequency of Operation

Once per driving cycle

TYPICAL ENABLING CONDITIONS

Battery voltage

11 V or higher

Intake air temperature

-10°C (14°F) or higher

Engine coolant temperature

75°C (167°F) or higher

Atmospheric pressure

76 kPa(abs) [570 mmHg(abs)] or higher

Idling

Off

Engine speed

Less than 4000 rpm

Air fuel ratio sensor status

Activated

Fuel system status

Closed loop

Engine load

10% or higher, and less than 80%

All of the following conditions are met

-

1. Mass air flow rate

2.5 gm/sec or more, and less than 50 gm/sec

2. Front catalyst temperature (estimated)

610°C (1130°F) or higher, and less than 840°C (1544°F) (for CVT models)

630°C (1166°F) or higher, and less than 840°C (1544°F) (for manual transaxle models)

3. Rear catalyst temperature (estimated)

400°C (752°F) or higher, and less than 800°C (1472°F)

CATALYST LOCATION

A291658C01

*1

Air Fuel Ratio Sensor (Sensor 1)

*2

Heated Oxygen Sensor (Sensor 2)

*3

Exhaust Manifold Sub-assembly

*4

TWC: Front Catalyst

*5

TWC: Rear Catalyst

*6

Front Exhaust Pipe Assembly

*7

Tail Exhaust Pipe Assembly

-

-
Note:

Replace the front exhaust pipe assembly (*6) when catalyst replacement is necessary. (Excluding heated oxygen sensor (*2))

CONFIRMATION DRIVING PATTERN

Tip:

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

A283969E23

  1. Connect the GTS to the DLC3.

  2. Turn the ignition switch to ON.

  3. Turn the GTS on.

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

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

  6. Turn the ignition switch to ON and turn the GTS 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].

    CAUTION:

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

    Tip:

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

  9. Turn the ignition switch off and wait for at least 30 seconds [C].

  10. Turn the ignition switch to ON and turn the GTS on.

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

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

    CAUTION:

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

    Tip:

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

  13. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [F].

  14. Read the pending DTCs.

    Tip:

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

    • If a pending DTC is not output, perform the following procedure.

  15. Drive the vehicle at a speed between 75 and 100 km/h (47 and 62 mph) for 10 minutes or more [G].

    CAUTION:

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

    Tip:

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

  16. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [H].

  17. Read the pending DTCs.

    Tip:

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

    • If a pending DTC is not output, system is normal.

CONDITIONING FOR SENSOR TESTING

Tip:

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.

A118003E74

  • (a) Connect the GTS to the DLC3.

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

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

  • (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 GTS.

Tip:

  • 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, perform the Control the Injection Volume for A/F Sensor Active Test using the GTS.

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

A199479E09

CAUTION / NOTICE / HINT

Tip:

  • If a malfunction cannot be found when troubleshooting DTC P0420, a lean or rich abnormality may be the cause. Perform troubleshooting by following the inspection procedure for P0171 (System Too Lean) and P0172 (System Too Rich).

  • 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 GTS. 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 GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    5. Read the DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTC P0420 is output

      A

      DTC P0420 and other DTCs are output

      B
      Tip:

      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 GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

    1. Connect the GTS to the DLC3.

    2. Start the engine and warm it up.

    3. Turn the GTS 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 / All Data / AFS Voltage B1S1 and O2S B1S2.

      Powertrain > Engine and ECT > Active Test

      Active Test Display

      Control the Injection Volume for A/F Sensor

      Data List Display

      AFS Voltage B1S1

      O2S B1S2

    6. Perform the Active Test operation with the engine idling (press the 12.5% or -12.5% 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 GTS.

      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.

      • 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.

      Standard

      GTS Display

      (Sensor)

      Injection Volume

      Status

      Voltage

      AFS Voltage B1S1

      (Air fuel ratio)

      12.5%

      Rich

      Below 3.1 V

      -12.5%

      Lean

      Higher than 3.4 V

      O2S B1S2

      (Heated oxygen)

      12.5%

      Rich

      Higher than 0.55 V

      -12.5%

      Lean

      Below 0.4 V

      Result

      Status AFS Voltage B1S1

      Status O2S B1S2

      Actual air fuel ratio, air fuel ratio sensor and heated oxygen sensor condition

      Misfire

      Main Suspected Trouble Area

      Proceed to

      Lean/Rich

      Lean/Rich

      Normal

      -

      • Three-way catalytic converter

      • Gas leak 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 leak from exhaust system

      C

      Lean/Rich

      Rich

      Heated oxygen sensor malfunction

      -

      • Heated oxygen sensor

      • Gas leak from exhaust system

      Lean

      Lean

      Actual air fuel ratio lean

      May occur

      • Extremely lean actual air fuel ratio

      • Gas leak from exhaust system

      D

      Rich

      Rich

      Actual air fuel ratio rich

      -

      • Extremely rich actual air fuel ratio

      • Gas leak 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 higher than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently below 0.4 V.

      Rich: During Control the Injection Volume for A/F Sensor, the AFS Voltage B1S1 is consistently below 3.1 V, and the O2S B1S2 is consistently higher 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 and heated oxygen sensor alternate correctly.

      Tip:

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

      Click here

    B

    REPLACE AIR FUEL RATIO SENSORClick here

    C

    CHECK FOR EXHAUST GAS LEAKClick here

    D

    CHECK FOR EXHAUST GAS LEAKClick here

    A

  3. CHECK FOR EXHAUST GAS LEAK

    1. Check the exhaust gas leaks.

      OK

      No gas leaks.

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINTClick here

    OK

  4. REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST)

    Note:

    Replace the front exhaust pipe assembly (TWC: Front and rear catalyst) when catalyst replacement is necessary.

    Tip:

    Confirm the replacement parts, referring to the illustration in the Catalyst Location.

    1. Replace the front exhaust pipe assembly (TWC: Front and rear catalyst).

      Click here

    Result

    Proceed to

    NEXT
    NEXT

    END

  5. REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    1. Repair or replace the exhaust gas leak point.

      Tip:

      Perform "Inspection After Repair" after repairing or replacing the exhaust system.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

  6. CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs.

      Powertrain > Engine and ECT > Clear DTCs

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

    6. Turn the ignition switch to ON.

    7. Turn the GTS on.

    8. Start the engine.

    9. Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

    10. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    11. Read the DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTC P0420 is output

      A

      DTC is not output

      (Pending DTC is not output)

      B
    B

    END

    A

  7. REPLACE FRONT EXHAUST PIPE ASSEMBLY (TWC: FRONT AND REAR CATALYST)

    Note:

    Replace the front exhaust pipe assembly (TWC: Front and rear catalyst) when catalyst replacement is necessary.

    Tip:

    Confirm the replacement parts, referring to the illustration in the Catalyst Location.

    1. Replace the front exhaust pipe assembly (TWC: Front and rear catalyst).

      Click here

    Result

    Proceed to

    NEXT
    NEXT

    END

  8. REPLACE AIR FUEL RATIO SENSOR

    1. Replace the air fuel ratio sensor.

      Click here

      Tip:

      Perform "Inspection After Repair" after replacing the air fuel ratio sensor.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

    CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)Click here

  9. CHECK FOR EXHAUST GAS LEAK

    1. Check the exhaust gas leaks.

      OK

      No gas leaks.

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINTClick here

    OK

  10. REPLACE HEATED OXYGEN SENSOR

    1. Replace the heated oxygen sensor.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

    CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)Click here

  11. CHECK FOR EXHAUST GAS LEAK

    1. Check the exhaust gas leaks.

      OK

      No gas leaks.

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINTClick here

    OK

  12. CHECK CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO

    1. Check the cause of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 Inspection Procedure.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

    CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)Click here