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

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors in the exhaust system.
2. Disconnect the electrical connectors from both sensors.
3. Use an O2 sensor socket or wrench to remove the sensors from the exhaust pipe.
4. Install the new upstream and downstream oxygen sensors by threading them into place and tightening to the manufacturer's specifications (typically 30-35 lb-ft).
5. Reconnect the electrical connectors securely.

3. Inspect and Replace Catalytic Converter

1. If the oxygen sensors are functioning properly, inspect the catalytic converter for damage.
2. Remove the exhaust pipes connected to the catalytic converter, typically requiring a socket set and possibly a penetrating oil for rusted bolts.
3. Carefully detach the catalytic converter from the exhaust manifold and the exhaust pipe.
4. Install the new catalytic converter, ensuring proper alignment with the exhaust system.
5. Torque the bolts to the specifications provided in the service manual (usually around 25 lb-ft).
6. Reinstall any heat shields that were removed during the process.

4. Reset the ECM

1. Reconnect the negative battery terminal.
2. Use the OBD-II scanner to clear the P0420 code from the ECM.
3. Start the engine and allow it to idle, monitoring for any check engine light re-illumination.