how to fix P0420 catalyst inefficiency code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.
• Raise the vehicle using jack stands for safe access to the exhaust system.

2. Inspect Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Remove the upstream and downstream oxygen sensors using a socket wrench.
• Inspect the sensors for damage or carbon buildup. If damaged, replace them.
• Reinstall the sensors and ensure they are securely tightened to manufacturer specifications.

3. Check Exhaust System

• Tools Required: Exhaust leak detection fluid or soapy water
• Visually inspect the exhaust for any cracks or holes; apply leak detection fluid to suspect areas to check for bubbles.
• If leaks are found, repair or replace the affected sections of the exhaust system.

4. Test Catalytic Converter

• Tools Required: Exhaust backpressure gauge
• Insert the backpressure gauge into the exhaust manifold or use a test port after the catalytic converter.
• Start the engine and measure the backpressure; it should be below the manufacturer’s specifications (typically less than 2.5 psi at idle).
• If backpressure is high, replace the catalytic converter.

5. Clear Codes and Test Drive

• Tools Required: OBD-II scanner
• After repairs, reconnect the battery and use the OBD-II scanner to clear the P0420 code.
• Perform a test drive to ensure the vehicle operates normally and the check engine light does not reappear.