Isn't the legal situation the opposite here? Car manufacturers don't release schematics because they believe in "free as in freedom". In fact any interfaces you as an end-user or an independent garage can use and schematics that are released such as the protocol for the diagnostic port, are open primarily because govermnents made laws saying so.
I'm most familiar with the "right to repair" situation with John Deere, which occasionally pops up on HN. The spirit of someone who releases something under GPL seems the opposite of that?