how to fix P0420 code on my Honda Civic 11th Generation (2022-Present)

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to prevent electrical shock.
• Allow the engine to cool down before starting work.

2. Oxygen Sensor Inspection

• Tools Required: OBD-II scanner, multimeter
• Remove the pre-catalytic and post-catalytic oxygen sensors using a socket wrench.
• Test the sensors with a multimeter:
  • Set the multimeter to measure voltage.
  • Start the engine and observe the pre-catalytic sensor voltage; it should fluctuate between 0.1V and 0.9V.
  • Check the post-catalytic sensor; it should have a steady voltage, indicating the catalytic converter is functioning properly.
• If either sensor is faulty, replace it with a new one.

3. Catalytic Converter Inspection

• Tools Required: Infrared thermometer, wrench set
• Measure the temperature at the inlet and outlet of the catalytic converter:
  • The inlet temperature should be lower than the outlet temperature by at least 100°F (38°C) for the converter to be functioning properly.
• If the outlet temperature is not significantly higher, the catalytic converter may be clogged or damaged and needs replacement.

4. Catalytic Converter Replacement

• Parts Required: New catalytic converter, new gaskets (if necessary)
• Remove the exhaust pipes and any heat shields that obstruct access to the catalytic converter using a wrench.
• Detach the old catalytic converter from the exhaust system.
• Install the new catalytic converter, ensuring that any gaskets are properly seated and torque bolts to manufacturer specifications.
• Reinstall any removed heat shields and exhaust pipes.

5. Final Steps

• Reconnect the negative battery terminal.
• Clear the check engine codes using the OBD-II scanner.
• Start the engine and let it idle for a few minutes to check for leaks and ensure the check engine light does not return.