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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle's battery to ensure safety.
• Raise the vehicle securely on jack stands if working underneath.

2. Inspect and Replace Oxygen Sensors

• Remove the upstream (pre-catalytic) oxygen sensor by disconnecting its electrical connector and using a socket wrench.
• Install the new oxygen sensor, ensuring it is tightened to manufacturer specifications (usually around 30 Nm).
• Repeat the process for the downstream (post-catalytic) oxygen sensor if it shows signs of malfunction.

3. Replace Catalytic Converter (if necessary)

• If the catalytic converter is damaged or clogged, remove it by loosening the bolts or clamps securing it to the exhaust system.
• Install the new catalytic converter, ensuring a proper fit and sealing.
• Torque the mounting bolts to the specifications provided by the manufacturer.

4. Clear Codes and Test Drive

• Reconnect the battery and use the OBD-II scanner to clear the P0420 code from the system.
• Start the engine and allow it to reach operating temperature.
• Conduct a test drive to monitor for any recurrence of the check engine light.