how to diagnose P0420 code in my Toyota Highlander XU70 (2020-Present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative terminal of the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream (pre-catalytic) oxygen sensor using the O2 sensor socket.
• Inspect the sensor for damage and replace if necessary.
• Install the new O2 sensor and torque to manufacturer specifications (typically around 30 ft-lbs).
• Repeat the process for the downstream (post-catalytic) oxygen sensor if it shows signs of failure.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool
• Remove the exhaust bolts securing the catalytic converter to the exhaust manifold and the exhaust pipe.
• Carefully lower the catalytic converter from the vehicle.
• Inspect for any physical damage or blockage.
• If damaged, install a new catalytic converter, ensuring to use OEM or high-quality aftermarket parts.
• Torque all bolts to the specifications provided in the service manual.

4. Reconnect Battery

• Reconnect the negative terminal of the battery.
• Ensure all tools are removed from the engine bay.

5. Clear Error Codes

• Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.