how can I fix the P0420 error code on my Honda Accord 8th Generation (2008-2012)?

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench.
• Remove the upstream (pre-catalytic converter) oxygen sensor:
  1. Use the O2 sensor socket to unscrew the sensor from the exhaust.
  2. Apply anti-seize compound on the threads of the new sensor.
  3. Install the new sensor and torque it to manufacturer's specifications (typically around 30 ft-lbs).
• Inspect and replace the downstream (post-catalytic converter) oxygen sensor if necessary, following the same procedure.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust hangers tool.
• If the oxygen sensors are functioning correctly but the code persists:
  1. Raise the vehicle safely using jack stands.
  2. Remove the exhaust system components leading to the catalytic converter.
  3. Disconnect the catalytic converter from its flanges using a socket set.
  4. Install the new catalytic converter, ensuring proper alignment and sealing.
  5. Torque the bolts to the specified value (usually around 25-30 ft-lbs).
  6. Reinstall the exhaust components and check for secure connections.

4. Reset the ECU

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the ECU.