[titanomachy]

Actually that's an interesting point you raise. The automaker provides you with a finished car containing finished machine code. It doesn't provide you with the CAD files needed to reproduce the car, the techniques used to built it, or the source needed to reproduce the machine code. And maybe they shouldn't be required to.

That said, I think it's reasonable to reverse engineer the code, just like you could physically take apart the car to figure out how it works. As long as you don't disseminate the results of that work, it shouldn't be illegal in my opinion. Even dissemination should be legal in some circumstances, like whistleblowing.