Need some advise 2021 Expedition 33,800 miles P0430 code dealer has replaced the cat and the code came right back after driving off the lot. Now they are going to replace the same cat again. But what could actually be causing the issue. The only code is the P0430 could there be a miss fire that the computer is not detecting I know in older fords they would not show a miss fire code unless it did it a lot. The driver side turbo waste gate sounds like it has a rattle at cold start which they are saying is normal. It seems to drive fine. If the cat is replaced again and the light still comes on what is normally the root cause at that point? There was a P0316 code that was stored in the memory that could have been old but was not causing the light to come on it was cleared and hasn't shown up since but the P0430 code has stayed constant even after replacement it has come on now 3 times with in 40 - 50 miles of it being cleared even after the cat replacement. Currently the dealer is saying the new cat could be bad that they just replaced yesterday.