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

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, multimeter, exhaust gas temperature (EGT) probe, safety glasses, gloves.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect Oxygen Sensors

• Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
• Use a multimeter to test the voltage output of the upstream sensor. It should fluctuate between 0.1V and 0.9V.
• If the upstream sensor is faulty, replace it.
• Check the downstream sensor's output; it should be relatively stable. Replace if it’s not functioning correctly.

3. Catalytic Converter Inspection

• Measure the temperature at the inlet and outlet of the catalytic converter using an EGT probe.
• The outlet temperature should be approximately 100-150°F higher than the inlet temperature. If not, the catalytic converter may be clogged or damaged.
• If the converter is faulty, remove it using a socket set, following these sub-steps:
  • Remove any heat shields or brackets securing the converter.
  • Unbolt the catalytic converter from the exhaust system.
  • Replace with a new catalytic converter, ensuring all gaskets are in place.

4. Reset the Engine Control Unit (ECU)

• Reconnect the battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the ECU.
• Start the vehicle and let it run for a few minutes to ensure no new codes appear.