how to fix the P0420 code on my Toyota Highlander Fourth Generation (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 battery terminal to prevent electrical shocks.

2. Inspect and Replace Oxygen Sensors (if faulty)

• Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
• Use an O2 sensor socket to remove the upstream sensor.
• Install the new upstream oxygen sensor and torque it to the manufacturer’s specifications (typically around 30 lb-ft).
• Repeat the process for the downstream oxygen sensor if it is also faulty.

3. Inspect and Replace Catalytic Converter (if necessary)

• Raise the vehicle using a jack and secure it with jack stands.
• Remove the exhaust system components connected to the catalytic converter, noting the position of each part.
• Unbolt the catalytic converter from the exhaust manifold and the downstream exhaust pipe.
• Replace with a new catalytic converter, ensuring proper alignment and sealing.
• Reinstall all exhaust system components and torque to specifications.

4. Check for Exhaust Leaks

• Start the engine and listen for any hissing sounds around the exhaust system.
• Use a smoke machine or soapy water to identify any leaks.
• Repair any leaks found in the exhaust system.