how to fix P0420 code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety during repairs.
• Allow the vehicle to cool down if the engine has been running.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench, multimeter
• Remove the upstream oxygen sensor (pre-catalytic converter) using an O2 sensor socket.
  • Check the wiring harness for any damage or corrosion; repair as necessary.
  • Install the new oxygen sensor and torque it to the manufacturer’s specification (usually around 30 ft-lbs).
• Repeat the process for the downstream oxygen sensor (post-catalytic converter) if it shows signs of failure.

3. Examine and Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust gasket
• Remove any heat shields or brackets securing the catalytic converter.
• Disconnect the exhaust pipes from the catalytic converter. Use penetrating oil if the bolts are rusted.
• Inspect the catalytic converter for any signs of blockage or damage such as dents or leaks.
• Replace with a new catalytic converter if it is damaged or clogged.
  • Ensure that the new converter is compatible with the model.
  • Reinstall using new gaskets and torque the bolts to manufacturer specifications.

4. Clear Codes and Test Drive

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