how to fix P0420 code on Honda Civic 10th Generation (2016-2021)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before starting work on the exhaust system.

2. Replace Oxygen Sensors (if faulty)

1. Locate the upstream and downstream oxygen sensors on the exhaust system.
2. Use an oxygen sensor socket to remove the old sensors.
3. Apply anti-seize compound to the threads of the new sensors.
4. Install the new sensors by hand to avoid cross-threading, then tighten to the manufacturer's specifications (typically around 30 lb-ft).
5. Reconnect the electrical connectors for the oxygen sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove any heat shields or brackets securing the catalytic converter using a socket set.
2. Unscrew the bolts connecting the catalytic converter to the exhaust manifold and the exhaust pipe.
3. Carefully remove the old catalytic converter from the exhaust system.
4. Install the new catalytic converter, ensuring it aligns correctly with the exhaust manifold and pipe.
5. Tighten the bolts to the manufacturer’s specifications (typically around 30 lb-ft).
6. Reattach any heat shields or brackets.

4. Clear Codes and Test Drive

1. Reconnect the negative battery terminal.
2. Use the OBD-II scanner to clear the P0420 code.
3. Start the engine and allow it to reach operating temperature.
4. Take the vehicle for a test drive to monitor performance and ensure the check engine light does not reappear.