how to fix Honda Civic 10th Generation (2016-2021) check engine light P0420

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery by removing the negative terminal to ensure safety while working on electrical components.

2. Inspect and Replace Oxygen Sensors

1. Locate the oxygen sensors: The upstream sensor is located in the exhaust manifold, and the downstream sensor is located after the catalytic converter.
2. Remove the upstream oxygen sensor: Use an oxygen sensor socket and turn counterclockwise to unscrew it.
3. Remove the downstream oxygen sensor: Follow the same procedure as above for the downstream sensor.
4. Install new oxygen sensors: Apply anti-seize compound to the threads of the new sensors. Tighten to manufacturer's specifications (typically around 30 ft-lbs).
5. Reconnect electrical connectors for both sensors.

3. Inspect and Replace the Catalytic Converter

1. Check for physical damage: Inspect the catalytic converter for any dents or signs of overheating.
2. Remove the exhaust system components: Use a socket set to remove any bolts securing the catalytic converter to the exhaust manifold and exhaust pipe.
3. Install the new catalytic converter: Position the new catalytic converter, and secure it with the original bolts. Torque the bolts to manufacturer specifications (usually around 25-30 ft-lbs).
4. Reattach any exhaust components that were removed during the process.

4. Clear Error Codes

1. Reconnect the battery: Ensure all connections are secure.
2. Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
3. Perform a test drive: Drive the vehicle for at least 10-15 miles to allow the engine control unit (ECU) to run diagnostics again.