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

Solution

1. Preparation

• Gather tools and parts. Ensure the vehicle is parked on a level surface and the engine is cool.
• Tools required: OBD-II scanner, multimeter, socket set, torque wrench, temperature probe.
• Safety warnings: Disconnect the battery before working on electrical systems. Ensure the vehicle is securely lifted if needed.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Disconnect the electrical connectors of both sensors.
3. Using a socket wrench, remove the sensors from the exhaust pipe.
4. Inspect the threads and ensure they are clean; replace if damaged.
5. Install the new sensors, applying anti-seize compound to the threads if recommended.
6. Tighten the sensors to the manufacturer’s specified torque.

3. Inspect and Replace the Catalytic Converter

1. Inspect the catalytic converter for physical damage or blockages.
2. If replacement is needed, first disconnect the exhaust pipes connected to the catalytic converter.
3. Remove any heat shields if necessary.
4. Unbolt the catalytic converter from its mounting points using the socket set.
5. Install the new catalytic converter by reversing the removal steps, ensuring all gaskets are replaced.
6. Tighten all bolts to the recommended torque specifications.

4. Clear Codes and Test

1. Reconnect the battery and use the OBD-II scanner to clear the P0420 code.
2. Start the engine and allow it to reach operating temperature.
3. Take the vehicle for a test drive under various conditions to ensure the check engine light does not reappear.