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

Solution

1. Preparation

• Gather tools and parts necessary for the repair.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to avoid electrical issues during repairs.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet and extension, torque wrench.
• Remove the upstream oxygen sensor (pre-catalytic converter) by:
  1. Using the O2 sensor socket to unscrew it.
  2. Installing the new oxygen sensor, ensuring to torque it to the manufacturer's specifications (usually around 30 ft-lbs).
• Repeat the process for the downstream oxygen sensor (post-catalytic converter) if necessary.

3. Inspect and Replace Catalytic Converter (if faulty)

• Tools Required: Socket set, cutting tool (if necessary), gasket scraper.
• Remove the exhaust manifold bolts and/or any bolts securing the catalytic converter:
  1. Disconnect any sensors attached to the catalytic converter.
  2. Remove the catalytic converter from the exhaust system. If it is welded, you may need to cut it out.
• Install the new catalytic converter:
  1. Position it in place and secure it with bolts.
  2. Reconnect any sensors removed during disassembly.
• Use a gasket scraper to clean the mating surfaces to ensure a proper seal.

4. Reconnect Battery and Clear Codes

• Reconnect the battery terminals securely.
• Use the OBD-II scanner to clear the P0420 error code and any other stored codes.