I think I didn't expand my comment enough. In this context (of software running a car), the manufacturer needs to provide a way of getting the GPL'd source code

I think I didn't expand my comment enough. In this context (of software running a car), the manufacturer needs to provide a way of getting the GPL'd source code to anyone that owns a vehicle with the relevant binary running in the car. Basically you don't lose your GPL software right if you've bought the car from someone else other than the manufacturer.