I'm such a paranoid that when I got my 1971 VW Superbeetle, I took the AM radio out.
...but true.
This is fascinating. From the 30th Chaos Communication Conference, this guy just wanted to add his own menu to the dashboard of his VAG car.
It's an hour long, but from 22:11 to 23:43 there is a good CAN Bus Crash Course. There are dominate and recessive bits; collisions aren't detected, they are arbitrated.
After that there is a lot of hackers laughing in the audience and it goes right down the rabbit hole.