my Toyota Highlander XU70 (2020-Present) has a check engine light with code P0420

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the battery to ensure safety while working on the electrical components.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, penetrating oil.
• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors in the exhaust system.
  2. Apply penetrating oil to the sensor threads and let it sit for a few minutes.
  3. Use the O2 sensor socket to carefully remove the sensors and inspect the connectors for damage.
  4. Replace any faulty sensors with new, OEM equivalent parts.
  5. Torque the new sensors to the manufacturer’s specifications (usually around 30 lb-ft).

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if applicable), gasket scraper.
• Sub-steps:
  1. If the catalytic converter is damaged or clogged, raise the vehicle securely on jack stands.
  2. Disconnect the exhaust pipes from the catalytic converter using the socket set.
  3. Remove any mounting brackets securing the catalytic converter.
  4. Replace the old catalytic converter with a new one, ensuring all gaskets and seals are in good condition before reinstallation.
  5. Reconnect the exhaust pipes and torque to manufacturer specifications.

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code and any other related codes.