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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to avoid electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream O2 sensor using the O2 sensor socket.
• Check the condition of the sensor; if it appears damaged or worn, replace it.
• Install the new O2 sensor, torque to manufacturer's specification (typically around 30 lb-ft).
• Repeat for the downstream O2 sensor if needed.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, cutting torch (if necessary), exhaust clamps or gaskets.
• Remove any exhaust components obstructing access to the catalytic converter (e.g., heat shields).
• Unbolt the catalytic converter from the exhaust system.
• Inspect for blockages or damage; if defective, replace it with a new catalytic converter.
• Install the new catalytic converter, ensuring all bolts and clamps are secure.

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use an OBD-II scanner to clear the P0420 code.
• Start the engine and let it run for a few minutes to ensure no codes reappear.