how to fix P0420 code in Honda Accord 8th Generation (2008-2012)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, multimeter
• If the oxygen sensors are faulty:
  1. Locate the upstream (pre-cat) and downstream (post-cat) oxygen sensors.
  2. Disconnect the electrical connectors for both sensors.
  3. Use the O2 sensor socket to unscrew the faulty sensors from the exhaust manifold and catalytic converter.
  4. Install new oxygen sensors, ensuring they are properly torqued to the manufacturer's specifications (typically around 30 ft-lbs).
  5. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, gasket scraper
• If the catalytic converter is confirmed to be faulty:
  1. Raise the vehicle and secure it on jack stands.
  2. Remove the heat shield (if applicable) by unscrewing the bolts.
  3. Disconnect the exhaust pipes from the catalytic converter using a socket set.
  4. Remove the catalytic converter from its mounting brackets.
  5. Clean the mating surfaces on the exhaust pipes with a gasket scraper.
  6. Install the new catalytic converter, ensuring it is properly aligned and secure.
  7. Reattach any exhaust pipes and torque to the manufacturer's specifications.
  8. Reinstall the heat shield if removed.

4. Clear Codes and Test

• Tools Required: OBD-II scanner
• After repairs:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code.
  3. Start the engine and let it reach operating temperature.
  4. Take the vehicle for a test drive to ensure the check engine light does not reappear.