how to fix P0420 code in Honda Civic 9th Generation (2012-2015)

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, socket set, torque wrench, infrared thermometer.
• Ensure the vehicle is parked on a flat surface and the engine is cool.

2. Inspect and Replace Oxygen Sensors

1. Disconnect the negative battery terminal.
2. Locate the upstream and downstream oxygen sensors (typically found in the exhaust manifold and after the catalytic converter).
3. Use a socket wrench to carefully remove the oxygen sensors.
4. Check the wiring and connectors for any damage; replace if necessary.
5. Install new oxygen sensors and torque them to the manufacturer's specifications (usually around 30 ft-lbs).
6. Reconnect the negative battery terminal.

3. Inspect and Replace Catalytic Converter (if necessary)

1. If the oxygen sensors are functioning correctly and the code persists, proceed with replacing the catalytic converter.
2. Raise the vehicle and securely support it with jack stands.
3. Remove the exhaust pipe connected to the catalytic converter using a socket set.
4. Detach any brackets or hangers securing the catalytic converter and remove it.
5. Install the new catalytic converter in the reverse order of removal. Ensure all gaskets and seals are in good condition.
6. Torque the exhaust connections to the specified values (refer to the service manual for exact torque specifications).

4. Final Checks

1. Reconnect the negative battery terminal.
2. Start the engine and check for exhaust leaks around the repair areas.
3. Allow the vehicle to reach operating temperature and verify that the check engine light does not reappear.