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

Solution

1. Preparation

• Gather tools and parts: OBD-II scanner, socket set, torque wrench, oxygen sensor socket, and safety glasses.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery negative terminal to prevent electrical issues.

2. Inspect and Replace Oxygen Sensors (if faulty)

1. Locate the upstream and downstream oxygen sensors. The upstream sensor is located before the catalytic converter, and the downstream sensor is after it.
2. Use an oxygen sensor socket to carefully remove the upstream oxygen sensor by turning it counterclockwise.
3. Install the new upstream oxygen sensor and torque it to the manufacturer's specifications (usually around 30-35 Nm).
4. Repeat the process for the downstream oxygen sensor if it is found to be faulty.
5. Reconnect the battery terminal.

3. Inspect and Replace the Catalytic Converter (if necessary)

1. If the catalytic converter is confirmed faulty (from the temperature test or other diagnostics), locate the catalytic converter in the exhaust system.
2. Disconnect any oxygen sensors connected to the catalytic converter.
3. Remove any mounting bolts or clamps securing the catalytic converter using a socket set (torque specifications may vary, generally 20-30 Nm).
4. Remove the old catalytic converter from the exhaust system.
5. Install the new catalytic converter in reverse order, ensuring that all gaskets are replaced and the bolts/clamps are torqued to the manufacturer's specifications.
6. Reconnect any oxygen sensors.

4. Final Checks

1. Start the engine and allow it to idle for a few minutes to check for any exhaust leaks.
2. Use the OBD-II scanner to clear the P0420 code and check if it reappears after driving the vehicle for a short distance.