what does it mean if my Toyota Highlander has a code P0420

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety during repairs.
• Ensure the vehicle is on a flat surface and use jack stands for safety if lifting the vehicle.

2. Inspect and Replace Oxygen Sensors

• Remove the upstream (pre-catalytic converter) oxygen sensor using an O2 sensor socket.
• Install the new oxygen sensor and torque to manufacturer's specifications (typically around 30 lb-ft).
• Repeat the process for the downstream (post-catalytic converter) oxygen sensor if necessary.

3. Catalytic Converter Inspection and Replacement

• If the catalytic converter is suspected to be damaged or clogged, proceed with removal:
  • Disconnect any heat shields and exhaust pipes connected to the catalytic converter.
  • Remove the mounting bolts securing the catalytic converter to the exhaust system.
  • Carefully lower the catalytic converter.
• Install the new catalytic converter:
  • Position the new catalytic converter and secure it with mounting bolts, torquing to specifications (usually around 25-30 lb-ft).
  • Reconnect any heat shields and exhaust pipes.

4. Final Checks

• Reconnect the battery.
• Start the vehicle and let it idle to check for any exhaust leaks.
• Clear the P0420 code using the OBD-II scanner and take the vehicle for a test drive to ensure the check engine light does not reappear.