I thought the routine was to use the sea foam or b12 when the tank was low and run for a while. I also thought there was a series of posts on this some time back. The theory is the cats get hotter and burn off build up. I just got one of the codes on the SVT and cleared to see if it comes back. My car is up for inspect and in NJ if the check engine light is on you will fail. They actually plug in the OBD II port during inspection.
Rich S
