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

Solution

1. Preparation

• Ensure the vehicle is parked on a level surface with the engine off and cool.
• Disconnect the battery to prevent any electrical issues during repairs.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, torque wrench
• Remove the upstream (pre-catalytic) oxygen sensor using the O2 sensor socket.
• Inspect the sensor for carbon buildup or damage. If defective, replace it with a new OEM or quality aftermarket sensor.
• Reinstall the new sensor and torque to manufacturer specifications (typically around 30-40 ft-lbs).
• Repeat for the downstream (post-catalytic) oxygen sensor if it shows signs of malfunction.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, cutting torch or saw (if necessary), exhaust gasket
• Inspect the catalytic converter for physical damage or signs of clogging.
• If replacement is needed, disconnect the exhaust pipes from the catalytic converter.
• Unbolt any mounting brackets or supports.
• Remove the old catalytic converter and replace it with a new OEM or quality aftermarket part.
• Reattach exhaust pipes and brackets, ensuring all connections are secure and leak-free.
• Use a new gasket where necessary and torque bolts to manufacturer specifications.

4. Clear Codes and Test

• Reconnect the battery.
• Use the OBD-II scanner to clear the P0420 code from the ECM.
• Start the engine and allow it to reach normal operating temperature.
• Perform a test drive to ensure the check engine light does not reappear.