What can't you do? Everytime I dig into this I discover someone wants to violate emissions laws. Sure you can change your throttle response without that, but the only people who want to are trying to break emissions.

I'm still waiting for an example of where DRM stops a normal repair

Well, first off, DMCA 1201 is part of copyright law; it's not a generic prohibition on removing any code that enforces a law. It's only for code or mechanisms that checks if you paid for a creative work. If you want a law that makes it illegal to tell people how to roll coal, pass a separate law that does just that. Bending copyright law to serve every imaginable prosocial benefit has inherent harms to it.

The example of DRM stopping normal repair is serialized parts: lots of vehicles, farm equipment, and phones are designed to refuse to work if you swap certain parts on them. The only way you are supposed to be able to swap parts is to pay the manufacturer's branded repair firms to make the swap for you, and then send some kind of signature to the computer in that vehicle that says the repair was authorized. Bypassing these schemes requires tampering with DRM code, which trips DMCA 1201. Yes, it may be legally unenforceable, but to get there requires a decade's worth of expensive litigation to prove that something that was legal before you put a computer in a car should be legal after you put a computer in a car. And even then you almost certainly can't distribute the tools you made to do what should be a legal repair because those tools might be used by someone else to pirate the ECU firmware or something.

Car owners like that as it means stealing a car for parts isn't worth it

The classic example is anything that's signed by crypto. So, often, pieces of the security systems or infotainment systems on a vehicle. But I was thinking more broadly, about other types of consumer products, once I started talking about Magnuson–Moss above.