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

Solution

1. Preparation

• Gather tools and parts required.
• Disconnect the negative battery terminal to prevent electrical shock.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Steps:
  1. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use the O2 sensor socket to remove the sensors from the exhaust manifold and catalytic converter.
  4. Install the new oxygen sensors by threading them into place and tightening to the manufacturer's torque specification (typically around 30 lb-ft).
  5. Reconnect the electrical connectors to the sensors.

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

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if applicable).
• Steps:
  1. Raise the vehicle securely using jack stands.
  2. Inspect the catalytic converter for damage or clogging.
  3. If replacement is needed, disconnect the exhaust pipes from both ends of the catalytic converter.
  4. Cut the exhaust pipes if they are welded.
  5. Install the new catalytic converter, ensuring proper orientation and fitment.
  6. Reconnect the exhaust pipes using clamps or welds as needed.

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner.
• Steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle’s system.
  3. Test drive the vehicle under various conditions to ensure the issue is resolved and the check engine light does not reappear.