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

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream (pre-catalytic) oxygen sensor:
  • Locate the sensor, disconnect the electrical connector, and use the O2 sensor socket to unscrew it.
• Install the new oxygen sensor:
  • Apply anti-seize compound to the threads of the new oxygen sensor.
  • Torque to manufacturer's specifications (typically around 30 ft-lbs).
• Repeat the process for the downstream (post-catalytic) oxygen sensor if necessary.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, penetrating oil (if needed).
• Remove the exhaust system components leading to the catalytic converter:
  • Use penetrating oil on bolts if they are rusted.
  • Disconnect any hangers or clamps.
• Remove the old catalytic converter:
  • Unscrew the bolts connecting the converter to the exhaust manifold and the exhaust pipe.
• Install the new catalytic converter:
  • Position the new converter and secure it with bolts.
  • Torque bolts to manufacturer's specifications.
• Reattach any exhaust components and hangers.

4. Clear Codes and Test

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Start the vehicle and allow it to reach operating temperature.
• Conduct a test drive to monitor for any reoccurrence of the check engine light.