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 heated oxygen sensor (sensor 1), sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor (sensor 2), 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 (sensor 1) 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 (sensor 2) is long, the oxygen storage capacity is great. There is a direct correlation between the heated oxygen sensor (sensor 2) 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 will illuminate the MIL and store this 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

Catalytic converter efficiency is low.

  • Exhaust manifold (catalytic converter)

  • Heated oxygen sensor (sensor 1 or 2)

Comes on

DTC stored

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 / Trouble Codes.

    5. Check for DTCs.

      Powertrain > Engine > 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. CHECK SENSOR INSTALLATION (HEATED OXYGEN SENSOR (SENSOR 1 AND 2))

    1. Check the heated oxygen sensor (sensor 1 and 2) installation condition.

      OK

      Heated oxygen sensor is installed correctly.

    Result

    Proceed to

    OK

    NG
    OK

    REPLACE EXHAUST MANIFOLD

    Click here

    NG

    REPLACE HEATED OXYGEN SENSOR (SENSOR 1 OR 2)