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

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, jack and jack stands, safety glasses, gloves.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent any electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Use a socket wrench to remove the upstream oxygen sensor.
3. Install the new upstream oxygen sensor and tighten to the manufacturer's torque specification (usually around 30 Nm).
4. Repeat for the downstream oxygen sensor if it was also found defective.
5. Reconnect the battery.

3. Check and Replace the Catalytic Converter (if necessary)

1. If the catalytic converter is damaged or clogged, lift the vehicle using a jack and secure with jack stands.
2. Remove the exhaust pipe connected to the catalytic converter using a socket set.
3. Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe.
4. Install the new catalytic converter, ensuring all gaskets and seals are in place.
5. Tighten all bolts to the specified torque settings (usually around 25-30 Nm for exhaust components).
6. Reconnect the exhaust pipe.

4. Final Checks

1. Reconnect the battery and start the engine.
2. Allow the engine to idle for a few minutes, then perform a test drive.
3. Monitor the vehicle for any check engine light reactivation.