Under US federal law auto makers in particular aren't allowed to deny warranty coverage to a car due to aftermarket modifications unless they can prove that tho

Under US federal law auto makers in particular aren't allowed to deny warranty coverage to a car due to aftermarket modifications unless they can prove that those specific modifications caused the problem. https://en.m.wikipedia.org/wiki/Magnuson–Moss_Warranty_Act https://en.m.wikipedia.org/wiki/Magnuson–Moss_Warranty_Act