how to diagnose 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 level surface and the engine is cool.

2. Clear Codes

• Connect the OBD-II scanner and clear the P0420 code.
• Start the engine and let it idle to check if the code reappears after a short drive.

3. Replace Defective Components

• Oxygen Sensor Replacement:

  1. Locate the upstream and downstream oxygen sensors.
  2. Disconnect the electrical connector from the sensor.
  3. Use a socket wrench to remove the old sensor.
  4. Apply anti-seize compound to the threads of the new sensor.
  5. Install the new sensor and reconnect the electrical connector.

• Catalytic Converter Replacement (if necessary):

  1. Raise the vehicle safely using jack stands.
  2. Remove the bolts securing the catalytic converter to the exhaust pipes using a socket set.
  3. Disconnect any hangers or brackets holding the converter.
  4. Remove the old catalytic converter.
  5. Install the new catalytic converter, ensuring proper alignment.
  6. Torque the bolts to the manufacturer's specifications.

4. Reassemble and Check

• Reinstall any components removed during the diagnostic process.
• Lower the vehicle and ensure all connections are secure.
• Start the engine and monitor for any exhaust leaks.