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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace O2 Sensors

• Tools Required: O2 sensor socket, wrench set
• Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
• Use the O2 sensor socket to carefully remove the sensors from the exhaust system.
• Inspect the sensors for carbon buildup or damage.
• If faulty, replace them with OEM or high-quality aftermarket parts.
• Reinstall the new sensors and reconnect the electrical connectors.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if necessary)
• Raise the vehicle using jack stands for access to the undercarriage.
• Inspect the catalytic converter for physical damage or excessive carbon buildup.
• If necessary, unbolt the catalytic converter from the exhaust system and remove it.
• Install a new catalytic converter, ensuring proper alignment with exhaust flanges.
• Torque the bolts to the manufacturer’s specifications (usually around 25-30 lb-ft, but verify in service manual).

4. Clear Codes and Test

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear any stored codes.
• Start the vehicle and allow it to reach operating temperature.
• Monitor the exhaust gases and engine performance during a test drive.