Code P0420?

The P0420 code means the catalyst system efficiency below threshold (Bank 1). So, this means the catalytic converter could be worn out or if the throttle has been wide open too long it will cause this code as well. I would clear the code and drive the car normally to see if it comes back. If it does here is a generic guide to help walk you through the catalytic converter replacement with instructions for your car in the diagrams below:

https://www.2carpros.com/articles/catalytic-converter-replacement

The catalytic converter is part of the exhaust manifold on your car. Check out the images (below). Please let us know what happens.