what should I do if my Honda Accord 8th Generation (2008-2012) shows P0420 code?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the exhaust system to cool before proceeding.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, penetrating oil.
• Remove the upstream oxygen sensor:
  • Apply penetrating oil to the sensor threads to ease removal.
  • Use the O2 sensor socket to unscrew the sensor.
• Replace with a new sensor, ensuring it is torqued to manufacturer's specifications (typically around 30 lb-ft).
• Repeat the process for the downstream sensor if needed.

3. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool.
• Remove the exhaust pipe or section containing the catalytic converter:
  • Loosen and remove the bolts or clamps securing the exhaust sections.
  • Support the exhaust system to prevent strain.
• Remove the catalytic converter from its mounting brackets.
• Install the new catalytic converter:
  • Position the new converter and secure it using the original or new bolts.
  • Torque the bolts to the manufacturer's specifications.

4. Final Checks

• Reconnect the negative battery terminal.
• Clear the trouble codes using the OBD-II scanner.
• Start the engine and allow it to reach operating temperature.