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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and is safe to work on.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, multimeter
  • Remove the oxygen sensors (upstream and downstream) from the exhaust system.
  • Use a multimeter to check the resistance and voltage of each sensor. Replace any faulty sensors with new ones.
  • Install the new sensors, ensuring they are torqued to manufacturer specifications.

3. Examine and Repair Exhaust System

• Tools Required: Socket set, exhaust repair kit (if needed)
  • Inspect the exhaust pipes, gaskets, and catalytic converter for leaks or damage.
  • If leaks are found, repair them using an exhaust repair kit or replace damaged components.
  • Ensure all connections are secure and leak-free.

4. Test Catalytic Converter

• Tools Required: Backpressure gauge
  • Connect a backpressure gauge to the O2 sensor port.
  • Start the engine and observe the gauge reading. A reading above 2.5 psi at idle indicates a clogged catalytic converter.
  • If clogged, replace the catalytic converter following manufacturer guidelines.

5. Reassemble and Reset

• Reconnect the battery.
• Clear the error codes using the OBD-II scanner.
• Ensure all components are securely fastened and check fluid levels.