"There are a number of things that could be causing this p0420 catalyst efficiency code. The most common thing is the catalytic converter itself is no longer functioning properly. The other likely thing is the rear O2 (oxygen) sensor is no longer working properly. Other things could include exhaust leaks, damaged exhaust pipes, damaged O2 sensor wiring/connectors, plugged catalytic converter, etc." got that from this link P0420 DTC Code - Catalyst System Efficiency Below Threshold (Bank 1) hope that helps
I have the same car and code. I'm currently on vaca for my bday but I would assume if you have the stock converters they are shot. They need to be replaced.
First a quick look at the rear o2 sensor on the passenger side to ensure its plunged in tight and not burned up.
I'm going to uninstall mine and shake it and listen if any piece is lose it rattles. If so I'm either going to bust out the remaining catalyst and get a tune to delete the rear o2 sensors or but new ones. I had already replaced mine a few years back with high flow cats but with my mods they didn't last long.