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

Solution

1. Preparation

• Gather necessary tools and materials.
• Disconnect the battery to prevent electrical shorts.
• Allow the engine to cool down before working on the exhaust components.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, multimeter
• Remove the upstream oxygen sensor using the O2 sensor socket.
• Inspect the wiring harness for damage; replace the sensor if defective.
• Install the new upstream oxygen sensor and torque to manufacturer specifications (typically around 30 lb-ft).
• Repeat the process for the downstream oxygen sensor if needed.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, exhaust pipe cutter or saw, gasket scraper
• Use an exhaust pipe cutter or saw to remove the exhaust pipe section leading to the catalytic converter.
• Unbolt the catalytic converter from the exhaust pipe and any brackets.
• Inspect the mounting surface and clean it thoroughly to ensure a proper seal.
• Install the new catalytic converter and secure it with new gaskets and bolts, tightening to manufacturer specifications (usually around 25-35 lb-ft).
• Reinstall the exhaust pipe section and secure it properly.

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner
• Reconnect the battery and use the OBD-II scanner to clear any fault codes.
• Start the engine and allow it to reach operating temperature.
• Perform a test drive to ensure the check engine light remains off and monitor for any return of symptoms.