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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on the vehicle.
• Allow the engine to cool down before starting the procedure.

2. Inspect and Replace Oxygen Sensors

• Inspect: Locate the upstream and downstream oxygen sensors. Remove them from their respective locations.
• Test: If testing indicated they are faulty, proceed to replace them.
• Install New Sensors: Apply anti-seize compound on the threads of the new sensors and install them, tightening to manufacturer specifications.

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

• Removal: Unbolt the exhaust pipes from the catalytic converter using a socket set. Ensure you have a replacement gasket ready.
• Inspect: Check the old catalytic converter for damage or clogging. If it appears damaged, proceed with replacement.
• Install New Converter: Position the new catalytic converter in place. Secure it with new bolts and gaskets, tightening to the specified torque.

4. Reconnect Battery and Clear Codes

• Reconnect the battery terminals.
• Use the OBD-II scanner to clear the P0420 code from the ECU.

5. Test Drive

• Start the vehicle and take it for a test drive to ensure the check engine light does not reappear and monitor for any unusual symptoms.