SFI SYSTEM, Diagnostic DTC:P0420

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

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 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 leak from exhaust system

  • Air fuel ratio sensor (sensor 1)

  • Heated oxygen sensor (sensor 2)

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

  • Center exhaust pipe assembly (TWC: Rear catalyst)

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

A01CDTOE01
Text in Illustration
*1 Exhaust Manifold Converter Sub-assembly (TWC: Front Catalyst) *2 Air Fuel Ratio Sensor (Sensor 1)
*3 Heated Oxygen Sensor (Sensor 2) *4 Front Exhaust Pipe Assembly
*5 Center Exhaust Pipe Assembly (TWC: Rear Catalyst) *6 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.

A01CCRKE37

Tech Tips


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

  • (b) Turn the engine switch on (IG).

  • (c) Turn the tester on.

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

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

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

  • (g) Start the engine and warm it up (Step "A").

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

  • (i) Those items will change to Compl (complete) after completing the drive pattern.

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

  • (k) Read the pending DTCs.

Tech Tips

If Catalyst Monitor does not change to Compl (complete), and any pending DTCs fail to be 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.

A01CFW4E73

  • (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 intelligent tester (Step "D").

Tech Tips


  • If either of the voltage outputs of the air fuel ratio or heated oxygen sensors 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 following menu items: 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).

A01CFZCE14

INSPECTION PROCEDURE

Tech Tips

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F sensor 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.

  3. Turn the tester on.

  4. Warm up 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 output voltages 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
-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.

Case

Air Fuel Ratio Sensor (Sensor 1)

Output Voltage

Heated Oxygen Sensor (Sensor 2)

Output Voltage

 Main Suspected Trouble Area
1 A01CDKHE08 A01CCPYE01 -
2 A01CD73E03 A01CCPYE01

  • Air fuel ratio sensor

  • Air fuel ratio sensor heater

  • Air fuel ratio sensor circuit
3 A01CDKHE08 A01CD73E03

  • Heated oxygen sensor

  • Heated oxygen sensor heater

  • Heated oxygen sensor circuit
4 A01CD73E03 A01CD73E03

  • Fuel pressure

  • Gas leakage from exhaust system

    (Air fuel ratio extremely lean or rich)

Tech Tips

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.

PROCEDURE


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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine 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. 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
        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 leakage 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 leakage from exhaust system

        		 C
        Lean/Rich Rich Heated oxygen sensor malfunction -

        • Heated oxygen sensor

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

        • Extremely lean actual air fuel ratio

        • Gas leakage from exhaust system

        		 D
        Rich Rich Actual air fuel ratio rich -

        • Extremely rich actual air fuel ratio

        • Gas leakage from exhaust system

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

        Rich: During the AFS 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.


    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. Check for exhaust gas leaks.

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

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


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


    NEXT

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

  5. INSPECT FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leaks.

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

    REPLACE HEATED OXYGEN SENSOR (SENSOR 2) Click here

  6. INSPECT FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leaks.

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

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