My understanding of the law (at least in California) is that if they determine the modification caused the problem work wont be covered under warranty, otherwise it has no negative affect.

Has anyone had bad experiences with mods and warranty repairs?

 

yeah thats pretty true...some crooked dealers will try and say that your mods caused the problem when they clearly didn't and most people will just go with it because they don't know any better

 

+1
I had a buddy of mine with a Ford F-150 that had tranny issues at two years and 31k miles.The dealer's service manager told him that since he had a cat back exhaust it constituted modifying his truck and that the estimated $1200 bill would not be covered under warranty.
He was so pissed he called me from his wife's car in the parking lot. I told him to go inside and tell the service mgr. that he just got off the phone with his atty, and his atty advised him that they would be getting a letter referring to the Magnuson/Moss Act whereby, a law suite would be filed. The service mgr. told him it would not be necessary, as he had "just" gotten off the phone with the regional rep, and they agreed, in the "essence" of good customer relations, to fix it under warranty. YEA, RIGHT!!!