GPLv3 contains the "Anti-TiVo" clause which requires that GPLv3 software be able to be swapped out with its equivalent from-source build by the end-user.
Most car manufacturers are very hesitant to give users access to swap out their car's software, often for warranty and safety reasons.
I can take a car to a repair shop of my choice, and replace the breaks. This is not illegal, nor does it invalidate some kind of "warranty". If the break is found to cause safety risk, it is not the car manufacturer that is going to get into trouble.
Why would there be a special warranty or safety concern replacing the software that control the break, but no warranty or safety concern replacing the physical breaks with custom ones?
I agree that there should be nothing illegal about modifying software, and that modifying software can't (or at least shouldn't) blanket-void a warranty.
My point was that since the burden is on the manufacturer to prove that they're denying a warranty claim due to a user's negligence or damage, manufacturers hate users modifying control software.
It's a lot easier to make a software change, damage a car, and reverse the change than it is to make a physical change, damage the car, and swap the part back before taking the part back to the dealer.
Plus, errors in software are much harder to spot. If I get a brake caliper bracket with a giant crack in it, I see the issue while I'm installing it and can send it back. If I download BillyJoe's Flash V1.65, I have to go to a lot more work to figure out if it's going to hurt me.
If the car crashes, I don't see how it would be easier to replace the offending physical part, or replacing the offending digital part.
However, its true that you might have a easier time to see a giant crack, but would you see material fatigue? would you see improper engineered breaks? Would you notice if instead of using steel in a critical point, they happened to use a more weaker metal like aluminum?
I guess the big difference is in user behavior. No one would go and buy BillyJoe's breaks from some alleyway, especially if it looked like they manufactured the stuff out of paste. However, some people might happily install breaks from an email attachment, sent by fishy Joes Nigeria email service. Especially if it said "Cheep UpGrade to the car braks!".
Im not sure if that should matter in the long run. It shouldn't require that government create a new law, like a Motor Vehicle Owners' Right to Repair software Act.
Most car manufacturers are very hesitant to give users access to swap out their car's software, often for warranty and safety reasons.