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

Solution

1. Preparation

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

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Remove the upstream (pre-catalytic converter) oxygen sensor using a socket wrench.
• Connect the multimeter to the oxygen sensor signal wire and ground.
• Start the engine and let it idle. Check for a switching voltage between 0.1V and 0.9V. If the sensor is not functioning properly, replace it.

3. Check Catalytic Converter

• Inspect the catalytic converter for any physical damage or signs of overheating (e.g., discoloration).
• If damage is found, replace the catalytic converter.
• If no visual issues are present, perform a backpressure test to check for blockage.

4. Replace Components (if necessary)

• If the upstream oxygen sensor or catalytic converter is faulty, replace with OEM or equivalent parts.
• Ensure all gaskets and seals are replaced to prevent exhaust leaks.
• Reinstall the new components securely.

5. Reassemble and Reconnect

• Reinstall any removed components in reverse order of disassembly.
• Reconnect the negative battery terminal.
• Clear the P0420 code using the OBD-II scanner.