My mechanic ran the OBD test. Came up with the 0420 code...O2 senosors are working..it's the cats. He recommended trying the Cataclean before replacing them. I've seen people clean them with laqueur thinner, but don't think it's safe. Many people seem to have used the product with decent results.You probably don't need new cats.
What makes you think you do? Search P0420 if that is your code. Our cats RARELY fail, but they are expensive to replace so repair folks like to suggest that is what needs to be done.