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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle's battery to prevent electrical shorts or shocks during repairs.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Steps:
  1. Locate the upstream (pre-cat) and downstream (post-cat) oxygen sensors.
  2. Use the O2 sensor socket to carefully remove the faulty oxygen sensors.
  3. Install new oxygen sensors, ensuring they are torqued to manufacturer specifications (usually around 30-40 ft-lbs).
  4. Reconnect the battery.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if needed), gasket scraper, high-temperature exhaust sealant.
• Steps:
  1. Safely lift the vehicle using a jack and secure it with jack stands.
  2. Remove the exhaust pipe connections to the catalytic converter using a socket set.
  3. Cut the exhaust pipe if it is rusted or damaged and cannot be removed.
  4. Remove the catalytic converter and inspect it for signs of damage or clogging.
  5. Clean the mating surfaces with a gasket scraper.
  6. Install a new catalytic converter, ensuring proper alignment.
  7. Reconnect all exhaust pipes, securing them tightly and using high-temperature exhaust sealant as needed.
  8. Lower the vehicle back to the ground.

4. Clear the Codes

• Tools Required: OBD-II scanner.
• Steps:
  1. Use the OBD-II scanner to clear the P0420 error code from the vehicle's computer.
  2. Start the engine and let it run for a few minutes to ensure no codes reappear.