how to fix P0420 code in Toyota Highlander Fourth Generation (2020-present) when it keeps returning?

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the vehicle battery to ensure safety.
• Allow the engine to cool down if it has been running.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
• Remove the oxygen sensors using the O2 sensor socket.
• Inspect the sensors for signs of wear or contamination.
• If faulty, replace the sensors with OEM or quality aftermarket parts.
• Torque the new sensors to the manufacturer’s specifications.

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

• Tools Required: Socket set, jack and jack stands, exhaust sealant
• Elevate the vehicle and support it securely.
• Detach the exhaust pipes connected to the catalytic converter.
• Remove the catalytic converter from its mounting brackets.
• Inspect for any damage; if damaged, replace with a new catalytic converter.
• Reinstall the new catalytic converter, ensuring a proper fit.
• Use exhaust sealant on joints to prevent leaks.

4. Clear Codes and Test Drive

• Reconnect the battery and use the OBD-II scanner to clear the P0420 code.
• Start the vehicle and allow it to reach operating temperature.
• Conduct a test drive under various conditions to ensure the code does not return.