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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Raise the vehicle securely on jack stands.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream oxygen sensor by using the O2 sensor socket and ratchet.
• Install the new upstream oxygen sensor by threading it into place and tightening it to the manufacturer’s torque specification (usually around 30 lb-ft).
• Repeat the process for the downstream oxygen sensor if it is suspected to be faulty.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if necessary).
• Remove the bolts securing the catalytic converter to the exhaust system using a socket set.
• If applicable, cut the exhaust pipe using an exhaust pipe cutter to detach the catalytic converter.
• Install the new catalytic converter by aligning it with the exhaust system and securing it with bolts, torquing to the manufacturer’s specifications.
• Ensure all gaskets and seals are replaced to prevent leaks.

4. Reconnect the Battery and Clear Codes

• Reconnect the battery terminals.
• Use the OBD-II scanner to clear the P0420 code from the ECM.
• Start the engine and let it idle to ensure the check engine light does not reappear.