SFI SYSTEM, Diagnostic DTC:P0420

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 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.

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

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.

• (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").

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, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.

• 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).

CAUTION / NOTICE / HINT

PROCEDURE

1. Click here

   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 DTCs.

      Table 3. 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.

   
   
   • AClick here
   • B

     GO TO DTC CHART (Click here)

2. Click here

   PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME)

   
   

   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.

   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.

      Tip:
      

      • Change the fuel injection volume within the range of -12% to +12%. The injection volume can be changed in fine gradations.

      • 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
        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

        Table 4. 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	-	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, 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, 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 of the Active Test, the output voltage of the heated oxygen sensor alternates correctly.

   
   
   • AClick here
   • BClick here
   • CClick here
   • DClick here
3. Click here

   CHECK FOR EXHAUST GAS LEAK

   
   

   1. Check for exhaust gas leaks.

      OK
      No gas leaks.

   
   
   • OKClick here
   • NGClick here
4. Click here

   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.

      Tip:

      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. Confirm that the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

      OK
      MAP and idling condition change in response to EGR step position.
      - 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 48 kPa (150 to 360 mmHg) (EGR valve is fully closed) MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

      Tip:
      

      • 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.

      • During Active Test, if the idling condition does not change in response to EGR step position, then there is probably a malfunction in the EGR valve.

      Table 5. Result

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

   
   
   • AClick here
   • BClick here
5. Click here

   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.

   
   
   • OKClick here
   • NGClick here
6. Click here

   REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT CATALYST) AND FRONT EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)

   Note:

   Replace the exhaust manifold converter (TWC: Front catalyst) and the front exhaust pipe assembly (TWC: Rear catalyst) together when catalyst replacement is necessary.

   Tip:

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

   
   

   1. Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst) (Click here).

   2. Replace the front exhaust pipe assembly (TWC: Rear catalyst) (Click here).

   
   
   • NEXT

     END

7. Click here

   REPLACE AIR FUEL RATIO SENSOR (BANK1 SENSOR1)

   
   

   1. Replace the air fuel ratio sensor (bank 1 sensor 1) (Click here)

      Tip:

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

   
   
   • NEXTClick here
8. Click here

   CHECK FOR EXHAUST GAS LEAK

   
   

   1. Check for exhaust gas leaks.

      OK
      No gas leaks.

   
   
   • OKClick here
   • NGClick here
9. Click here

   REPLACE HEATED OXYGEN SENSOR (BANK1 SENSOR2)

   
   

   1. Replace the heated oxygen sensor (bank 1 sensor 2) (Click here)

   
   
   • NEXTClick here
10. Click here

    CHECK FOR EXHAUST GAS LEAK

    
    

    1. Check for exhaust gas leaks.

       OK
       No gas leaks.

    
    
    • OKClick here
    • NGClick here
11. Click here

    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.

       Tip:

       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. Confirm that the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

       OK
       MAP and idling condition change in response to EGR step position.
       - 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 48 kPa (150 to 360 mmHg) (EGR valve is fully closed) MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

       Tip:
       

       • 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.

       • During Active Test, if the idling condition does not change in response to EGR step position, then there is probably a malfunction in the EGR valve.

       Table 6. Result

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

    
    
    • AClick here
    • BClick here
12. Click here

    INSPECT EGR VALVE ASSEMBLY (VISUALLY CHECK EGR VALVE)

    
    

    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.

    
    
    • OKClick here
    • NGClick here
13. Click here

    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)

    
    
    • NEXTClick here
14. Click here

    REPLACE EGR VALVE ASSEMBLY

    
    

    1. Replace the EGR valve assembly (Click here).

       Tip:

       Perform "Inspection After Repairs" after replacing the EGR valve assembly (Click here).

    
    
    • NEXTClick here
15. Click here

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    
    

    1. Repair or replace exhaust gas leak point.

       Tip:

       Perform "Inspection After Repairs" after repairing or replacing the exhaust system (Click here).

    
    
    • NEXTClick here
16. Click here

    CHECK WHETHER DTC OUTPUT RECURS (DTC P0420)

    
    

    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

    4. Clear the DTCs (Click here).

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

    6. Turn the ignition switch to ON.

    7. Turn the tester 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 /DTC.

    11. Read DTCs.

        Table 7. Result

        Result	Proceed to
        DTC P0420 is output	A
        DTC is not output (No pending DTCs output)	B

    
    
    • AClick here
    • B

      END

17. Click here

    REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT CATALYST) AND FRONT EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)

    Note:

    Replace the exhaust manifold converter (TWC: Front catalyst) and the front exhaust pipe assembly (TWC: Rear catalyst) together when catalyst replacement is necessary.

    Tip:

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

    
    

    1. Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst) (Click here).

    2. Replace the front exhaust pipe assembly (TWC: Rear catalyst) (Click here).

    
    
    • NEXT

      END