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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Allow the exhaust system to cool before working on it.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench, penetrating oil.
• Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
• Apply penetrating oil to the threads of the sensors if they are rusty or difficult to remove.
• Disconnect the wiring harness from each O2 sensor.
• Remove the sensors using the O2 sensor socket.
• Compare the old sensors with new ones; replace if they are faulty.
• Install new sensors and torque them to the manufacturer's specifications (typically around 30 lb-ft).

3. Inspect or Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, gasket scraper.
• Inspect the catalytic converter for physical damage or signs of clogging.
• If replacement is necessary, unbolt the catalytic converter from the exhaust system.
• Use a gasket scraper to remove old gasket material from the flanges.
• Install the new catalytic converter, ensuring that the exhaust gaskets are in place.
• Torque the bolts to manufacturer's specifications (usually around 30 lb-ft).

4. Clear Fault Codes

• Reconnect the battery and use an OBD-II scanner to clear the P0420 code from the system.
• Start the engine and allow it to reach operating temperature.