SFI SYSTEM (w/ Secondary Air Injection 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 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 a 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 a DTC.

DTC No. DTC Detection Conditions Trouble Areas
P0420

OSC value smaller than standard value under active air-fuel ratio Control

(2 trip detection logic)

  • Exhaust pipe assembly front (three-way catalytic converter)

  • Gas leakage from exhaust system

  • Air-Fuel Ratio (A/F) sensor (sensor 1)

  • Heated Oxygen (HO2) sensor (sensor 2)

CONFIRMATION DRIVING PATTERN

Tech Tips

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the A/F and HO2 sensors. This is in order to activate the sensors sufficiently to obtain the appropriate inspection results.

A01BEIDE09

1. Connect the intelligent tester to the DLC3 (1).

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

3. Run the engine at an engine speed of between 2,500 rpm and 3,000 rpm for at least 3 minutes (3).

4. While running the engine at 3,000 rpm for 2 seconds and 2,000 rpm for 2 seconds, check the waveforms of the A/F and HO2 sensors using the tester or scan too (4)l.

Tech Tips


  • If either of the voltage outputs of the Air-Fuel Ratio (A/F) or Heated Oxygen (HO2) sensor does not fluctuate, or either of the sensors makes a noise, 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 Control the Injection Volume for A/F Sensor using an intelligent tester.

  • 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 control is not performed).

A01BDLRE01

Tech Tips

When using an intelligent tester only:

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the Air-Fuel Ratio (A/F) sensor, Heated Oxygen (HO2) 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 an intelligent tester.

CONDITIONING FOR SENSOR TESTING

Tech Tips

When using an intelligent tester only:

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the Air-Fuel Ratio (A/F) sensor, Heated Oxygen (HO2) 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 an intelligent tester.


  1. Connect an intelligent tester to the DLC3.

  2. Start the engine and turn the tester ON.

  3. Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.

  4. On the tester, select the following menu items: 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.

  6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS Voltage B1S1 and OS2 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.

Voltage

Tester Display

(Sensor)

 Injection Volumes Status Voltages

AFS Voltage B1S1

(A/F)

 +25 % Rich Less than 3.1

AFS Voltage B1S1

(A/F)

 -12.5 % Lean More than 3.4

O2S B1S2

(HO2)

 +25 % Rich More than 0.5

O2S B1S2

(HO2)

 -12.5 % Lean Less than 0.4

CAUTION:

The Air-Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2) sensor has a maximum output delay of approximately 20 seconds.

Case

A/F Sensor (Sensor 1)

Output Voltage

HO2 Sensor (Sensor 2)

Output Voltage

Mainly Suspected

Trouble Areas
1

Injection volume

+25 %

-12.5 %

 A01BAGF

Injection volume

+25 %

-12.5 %

 A01BAGF -

Output voltage

More than 3.4 V

Less than 3.1 V

 A01BF8P

Output voltage

More than 0.5 V

Less than 0.4 V

 A01BBCR
2

Injection volume

+25 %

-12.5 %

 A01BAGF

Injection volume

+25 %

-12.5 %

 A01BAGF

  • A/F sensor

  • A/F sensor heater

  • A/F sensor circuit

Output voltage

Almost no reaction

 A01BD50

Output voltage

More than 0.5 V

Less than 0.4 V

 A01BBCR
3

Injection volume

+25 %

-12.5 %

 A01BAGF

Injection volume

+25 %

-12.5 %

 A01BAGF

  • HO2 sensor

  • HO2 sensor heater

  • HO2 sensor circuit

Output voltage

More than 3.4 V

Less than 3.1 V

 A01BF8P

Output voltage

Almost no reaction

 A01BD50
4

Injection volume

+25 %

-12.5 %

 A01BAGF

Injection volume

+25 %

-12.5 %

 A01BAGF

  • Injector

  • Fuel pressure

  • Gas leakage from exhaust system

(Air-fuel ratio extremely lean or rich)

Output voltage

Almost no reaction

 A01BD50

Output voltage

Almost no reaction

 A01BD50

INSPECTION PROCEDURE

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 an intelligent tester to the DLC3.

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

    3. Select the following menu items: Powertrain / Engine and ECT / DTC.

    4. Read DTCs.

      Result
      Display (DTC Output) 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

    A

  2. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (A/F 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 2,500 rpm for approximately 90 seconds.

    4. On the tester, select the following menu items: 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.

    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 25 %.

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

      Voltage

      Tester Display

      (Sensor)

      		 Injection Volumes Status Voltages

      AFS Voltage B1S1

      (A/F)

      		 +25 % Rich Less than 3.1

      AFS Voltage B1S1

      (A/F)

      		 -12.5 % Lean More than 3.4

      O2S B1S2

      (HO2)

      		 +25 % Rich More than 0.5

      O2S B1S2

      (HO2)

      		 -12.5 % Lean Less than 0.4
      Result

      Status

      AFS Voltage B1S1

      Status

      O2S B1S2

      		 A/F Condition and A/F and HO2 Sensors Condition Misfires Main Suspected Trouble Areas Proceed To
      Lean/Rich Lean/Rich Normal -

      • Three-Way Catalytic Converter (TWC)

      • Gas leakage from exhaust system

      		 A
      Lean Lean/Rich A/F sensor malfunction -

      • A/F sensor malfunction

      		 B
      Rich Lean/Rich A/F sensor malfunction -

      • A/F sensor malfunction

      		 B
      Lean/Rich Lean HO2 sensor malfunction -

      • HO2 sensor

      • Gas leakage from exhaust system

      		 C
      Lean/Rich Rich HO2 sensor malfunction -

      • HO2 sensor

      • Gas leakage from exhaust system

      		 C
      Lean Lean Actual air-fuel ratio lean May occur

      • Extremely rich or lean actual air-fuel ratio

      • Gas leakage from exhaust system

      		 A
      Rich Rich Actual air-fuel ratio lean -

      • Extremely rich or lean actual air-fuel ratio

      • Gas leakage from exhaust system

      		 A

      Lean: During Control the Injection Volume for A/F Sensor, the A/F sensor output voltage (AFS) is consistently more than 3.4 V, and the HO2 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 0.5 V.

      Lean/Rich: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the HO2 sensor alternates correctly.


    B

    CHECK AND REPLACE AIR FUEL RATIO SENSOR

    C

    INSPECT HEATED OXYGEN SENSOR Click here

    A

  3. CHECK FOR EXHAUST GAS LEAKAGE

    OK
    No gas leakage.

    Note

    Replace both the front and rear catalysts (front exhaust pipe).


    NG

    REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT

    OK

    REPLACE EXHAUST PIPE ASSEMBLY FRONT (THREE-WAY CATALYTIC CONVERTER)

  4. INSPECT HEATED OXYGEN SENSOR


    1. A01BHKCE01

      Disconnect the D35 Heated Oxygen (HO2) sensor connector.

    2. Measure the resistance between the terminals of the HO2 sensor connector.

      Resistance
      Tester Connections Specified Conditions
      HT1B (1) - +B (2) 11 to 16 Ω at 20°C (68°F)
      HT1B (1) - E2 (4) 10 kΩ or higher

    3. Reconnect the HO2 sensor connector.


    NG

    REPLACE HEATED OXYGEN SENSOR

    OK

    REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT