I had my CEL read at Autozone today and it was P3040. I searched the forums and a lot of people say its related to the alternator but I've been driving with this CEL for the past 2 months or so(I know I shouldn't have waited this long) and the cars been driving 100% normal during city driving interstate driving and highly spirited driving so I'm thinking it can't be the alternator because if it started dieing months ago I think it would have went out by now, anybody experience this problem?

 

https://themustangsource.com/f637/tr...-p0349-494953/

Might help

 

Had the same code come up for me and drove the car for sometime, I was even able to clear the cel until it permanently stayed on.. I took it to Autozone to have the charging system checked out and sure enough it was the alternator going bad.

Replaced the alternator and the cell went away.