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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery to prevent electrical shorts.
• Allow the engine to cool completely before starting the work.

2. Inspect and Replace Oxygen Sensors (if necessary)

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors (typically near the exhaust manifold and after the catalytic converter).
  2. Disconnect the electrical connectors from both sensors.
  3. Use an O2 sensor socket to remove the sensors from the exhaust system.
  4. Install new oxygen sensors, tightening them to the manufacturer’s torque specifications (usually around 30-40 ft-lbs).
  5. Reconnect the electrical connectors to each sensor.

3. Inspect and Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if needed)
• Sub-steps:
  1. Remove any heat shields or covers obstructing access to the catalytic converter.
  2. Disconnect the exhaust pipes from the catalytic converter using a socket set.
  3. If necessary, cut the exhaust pipe with an exhaust pipe cutter to remove the old catalytic converter.
  4. Install the new catalytic converter, ensuring proper alignment.
  5. Reconnect the exhaust pipes and secure with appropriate hardware, torquing to manufacturer specifications.
  6. Reinstall any heat shields or covers that were removed.

4. Clear Error Codes and Test Drive

• Tools Required: OBD-II scanner
• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
  3. Start the engine and let it idle for a few minutes.
  4. Take the vehicle for a test drive under various driving conditions to ensure the check engine light does not reappear.