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

Solution

1. Preparation

• Gather all 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. Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Sub-steps:
  1. Locate the upstream (before the catalytic converter) and downstream (after the catalytic converter) oxygen sensors.
  2. Unplug the electrical connectors from both sensors.
  3. Use the O2 sensor socket to remove the sensors from the exhaust system.
  4. Apply anti-seize compound to the threads of the new sensors.
  5. Install the new sensors, tightening to the manufacturer's specified torque (usually around 30 lb-ft).
  6. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, jack and jack stands, exhaust gasket kit.
• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Locate the catalytic converter in the exhaust system.
  3. Remove any heat shields or brackets obstructing access.
  4. Unbolt the catalytic converter from the exhaust pipes, taking care to catch any exhaust gaskets.
  5. Inspect the converter for signs of damage or clogging.
  6. Install the new catalytic converter using new gaskets and tighten the bolts to specifications (typically around 25 lb-ft).
  7. Reinstall any heat shields or brackets removed earlier.

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
  3. Start the engine and allow it to reach operating temperature.
  4. Take the vehicle for a test drive under various conditions (city and highway) to ensure the code does not return.