how to fix Honda Civic 9th Generation (2012-2015) check engine light with P0420 code?

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Inspect the upstream (pre-catalytic) oxygen sensor for proper function.
• If faulty, remove the upstream oxygen sensor by using the O2 sensor socket and replace it with a new one, tightening to the manufacturer’s specified torque (typically around 30 lb-ft).
• Repeat for the downstream (post-catalytic) oxygen sensor if necessary.

3. Check and Replace Catalytic Converter (if needed)

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if necessary).
• If the catalytic converter is confirmed faulty, unbolt the exhaust pipe from the catalytic converter using the socket set.
• If it is welded, use an exhaust pipe cutter to remove it.
• Install the new catalytic converter in reverse order of removal, ensuring all gaskets are replaced and fasteners are torqued to manufacturer specifications.

4. Clear Codes and Test Drive

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Test drive the vehicle to ensure the check engine light does not return.