how to fix P0420 code on Honda Accord 10th Generation (2018-2022)

Solution

1. Preparation

• Gather tools and parts required.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the exhaust system to cool before working on it.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench, penetrating oil.
• If the oxygen sensors are faulty:
  1. Locate the upstream and downstream oxygen sensors.
  2. Apply penetrating oil to the sensor threads and allow it to sit for a few minutes.
  3. Using the O2 sensor socket, unscrew the faulty sensor(s) from the exhaust.
  4. Install the new sensor by threading it in by hand and then tightening it to the manufacturer's torque specification (typically around 30 lb-ft).
  5. Reconnect the electrical connectors.

3. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust gasket, jack and jack stands.
• If the catalytic converter is damaged or ineffective:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Remove any heat shields or components obstructing access to the catalytic converter.
  3. Disconnect exhaust pipes leading to and from the catalytic converter using the appropriate socket.
  4. Remove the old catalytic converter and exhaust gaskets.
  5. Install the new catalytic converter using new gaskets, ensuring all bolts are tightened to the manufacturer's specifications.
  6. Reinstall any heat shields removed and lower the vehicle.

4. Reset the ECU

• After repairs, reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the ECU.