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

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, infrared thermometer, socket set, jack and jack stands.
• Safety Warnings: Disconnect the battery before working on electrical components, allow the engine to cool before performing any work on the exhaust system.

2. Oxygen Sensor Inspection

1. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Disconnect the electrical connectors from both sensors.
3. Use a multimeter to check the voltage output of the upstream sensor; it should fluctuate between 0.1 and 0.9 volts.
4. Repeat the check for the downstream sensor; it should have less fluctuation than the upstream sensor.
5. Replace any faulty sensors.

3. Catalytic Converter Replacement

1. If the oxygen sensors are functioning properly, prepare to replace the catalytic converter.
2. Lift the car safely using a jack and secure it with jack stands.
3. Remove the exhaust heat shield if applicable, using a socket set.
4. Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe, noting any gaskets that may require replacement.
5. Install the new catalytic converter, ensuring proper alignment and using new gaskets where necessary.
6. Torque the bolts to the manufacturer’s specifications (typically around 25-30 lb-ft but check the service manual for specifics).

4. Reassembly and Final Checks

1. Reinstall any heat shields removed earlier.
2. Reconnect the battery.
3. Start the engine and let it idle to check for leaks at the exhaust joints.
4. Drive the vehicle for a short distance to ensure the check engine light does not return.