Let me start by saying I have a 2004 Mazda 6 and a couple months ago I hit a deer. And my airbags were deployed .I had a mechanic replace the radiator and core support and coolant system plus the bumper fender and headlight ....I don't think he put the piece of plastic that goes under your bumper back on when he replaced it and there's been possibly mud and other debris getting up into my wiring ..I replaced my alternator 2 months ago but since he worked on it it has been overcharging my battery to like 18 To the point I've replaced the battery a week ago .. it has occasionally been going into limp mode and slamming me into 3rd gear ....but my alternator is good , could it possibly be a bad wire going to my pcm causing it to spit out a bad code which is making my alternator overcharge my battery ?? I do think it's a wiring issue but any help with this would be greatly appreciated .I love the little car and hate to get rid of it but if the repairs are going to be more than the car is worth I'd like to know .....Thanks

 

Alternator is controlled by the PCM.