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

Solution

1. Preparation

• Gather all necessary tools and parts for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool completely before starting work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, OBD-II scanner
• Remove the upstream (pre-cat) and downstream (post-cat) oxygen sensors using the O2 sensor socket.
• Inspect the wiring and connector for damage; replace if necessary.
• Install new oxygen sensors and ensure they are properly torqued according to the manufacturer's specifications.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if needed)
• Remove the exhaust pipes connected to the catalytic converter, ensuring to support the exhaust system.
• Inspect the catalytic converter for blockages or damage.
• If replacement is necessary, install a new catalytic converter, ensuring all gaskets are in good condition.
• Reconnect the exhaust pipes and torque to the manufacturer's specifications.

4. Clear Error Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.