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 (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 air fuel ratio control, rather than the conventional detecting method, which uses the locus ratio.

The OSC 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 rich-lean cycle of the HO2 sensor is long, the OSC becomes greater. There is a direct correlation between the OSCs of the HO2 sensor and 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 (OSC) value smaller than standard value under active air fuel ratio control

(2 trip detection logic)

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

  • Gas leak from exhaust system

  • Air fuel ratio sensor (sensor 1)

  • Heated oxygen sensor (sensor 2)

CATALYST LOCATION

A010IH9E01
Text in Illustration
*1 Exhaust Manifold *2 TWC: Front Catalyst
*3 Front Exhaust Pipe *4 TWC: Rear Catalyst
*5 Tail Exhaust Pipe - -

CONFIRMATION DRIVING PATTERN

Tech Tips

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

A010KUEE22

  1. Connect the intelligent tester to the DLC3.

  2. Turn the ignition switch to ON.

  3. Turn the tester 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 tester 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.

    Tech Tips

    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 tester 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.

    Tech Tips

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

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

  14. Read the pending DTCs.

    Tech Tips


    • 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.

    Tech Tips

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

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

  17. Read the pending DTCs.

    Tech Tips


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

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

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 (A/F) and Heated Oxygen (HO2) sensors. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.

A010I0GE44

  1. Connect an intelligent tester to the DLC3.

  2. Start the engine and warm it up with all the accessories switched OFF, until the engine coolant temperature stabilizes.

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

  4. While running the engine at 3000 rpm and 2000 rpm alternating at 2 second intervals, check the waveforms of the A/F and HO2 sensors using the tester.

Tech Tips


  • If either voltage output of the A/F or HO2 sensor does not fluctuate, or there is a noise in the waveform of either 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 Three-Way Catalytic Converter (TWC) has deteriorated, the HO2 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).

A010KE8E07

INSPECTION PROCEDURE

Tech Tips


  • 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).

  • Read freeze frame data using an intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. 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 an intelligent tester to the DLC3.

    2. Turn the ignition switch to ON and turn the tester on.

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

    4. Read DTCs.

      Result
      Result Proceed to
      P0420 A
      P0420 and other DTCs 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 (INJECTION VOLUME CONTROL)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine and turn the tester on.

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

    4. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F sensor.

    5. Perform the Control the Injection Volume for A/F sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).

    6. Monitor the voltage outputs of the A/F and HO2 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 12.5%.

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

      • 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

      (A/F)

      		 +12.5% Rich Below 3.1 V

      AFS Voltage B1S1

      (A/F)

      		 -12.5% Lean Higher than 3.4 V

      O2S B1S2

      (HO2)

      		 +12.5% Rich Higher than 0.55 V

      O2S B1S2

      (HO2)

      		 -12.5% Lean Below 0.4 V
      Result

      Status

      AFS Voltage B1S1

      Status

      O2S B1S2

      A/F Condition and A/F and

      HO2 Sensors Conditions

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

      • Three-Way Catalytic Converter (TWC)

      • Gas leak from exhaust system

      		 A
      Lean Lean/Rich A/F sensor malfunction

      • A/F sensor

      		 B
      Rich Lean/Rich A/F sensor malfunction

      • A/F sensor
      Lean/Rich Lean HO2 sensor malfunction

      • HO2 sensor

      • Gas leak from exhaust system

      		 C
      Lean/Rich Rich HO2 sensor malfunction

      • HO2 sensor

      • Gas leak from exhaust system
      Lean Lean Actual air-fuel ratio lean

      • Extremely rich or lean actual air fuel ratio

      • Gas leak from exhaust system

      		 D
      Rich Rich Actual air-fuel ratio rich

      • Extremely rich or lean 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) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.

      Rich: During Control the Injection Volume for A/F sensor, 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 air fuel ratio sensor and heated oxygen sensor alternates correctly.


    B

    REPLACE AIR FUEL RATIO SENSOR Click here

    C

    INSPECT FOR EXHAUST GAS LEAK Click here

    D

    CHECK EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO, REPAIR CAUSE AND GO TO NEXT STEP Click here

    A

  3. INSPECT FOR EXHAUST GAS LEAK


    1. Inspect for exhaust gas leakage.

      OK
      No gas leak.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

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

  4. INSPECT FOR EXHAUST GAS LEAK


    1. Inspect for exhaust gas leakage.

      OK
      No gas leak.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAK POINT

    OK

    REPLACE HEATED OXYGEN SENSOR Click here