Originally Posted by Focusedintntions
A warranty can't be voided period. However, if a part fails they can deny replacement of said part if they can prove that the aftermarket parts modification led to the failure. So if you swap in a catless DP and an o2 sensor goes you're probably sol, however, put in the catless dp and your maf or oil pump go they'll warranty the replacements. Make sense?
In a perfect world. In the real world they'll do whatever they want. They can ask you to pay for anything, claiming your warranty is voided for any part that isn't there's. You can Moss-Magnuson Act all you want, but they know that you aren't going to lawyer up over a $800 service bill.
It all comes down to how nice the dealership wants to be, or how inattentive they are to the fact that you even have non-OEM parts.