It could be the o2 sensor but 99% of the time a new cat will fix this dtc. I've been told that you can put a spark plug antifouler from autozone on the rear o2 sensors and even without cats this dtc won't set but I don't know if thats true or not. It wouldn't cost much to test the theory out and if it did then removing the cat would be possible if you don't have an emissions test to pass. Don't put an aftermarket cat on because they will create this code as well since most don't clean the exhaust as well as what the computer expects.