reply to Anonymous_
Re: catalytic converter? P0420 The OP would be wise to listen to the advice of mattmag. I too decided against paying $1200 for the OEM Buick cat and went to Rockauto and paid $200. Exactly a week after the 12 mos warranty expired I started getting a PO420 about every other week. Googled the problem and there is a lot of issues with PO420 and cheap replacement cats. Replacing the cat is the only answer.
I will add that I replaced the original OEM cat at 100k miles due to it being blocked.