This is a bit simplistic. By now, most cars will have multiple CAN buses, not least to separate the infotainment crap from the safety-critical subsystems like t

This is a bit simplistic. By now, most cars will have multiple CAN buses, not least to separate the infotainment crap from the safety-critical subsystems like the ECU, steering, ABS braking and others. Chances are the mandated diagnostic part you can access will not be able to control these subsystems (or even receive their messages). Of course a hardware air-gap is inconvenient when you are trying to ship subpar hardware and software on a shoestring budget, so the industry invented smart CAN "switches" and it's possible to escalate the access the diagnostic port provides, or tunnel from the infotainment network to the safety one. In newer cars, you can also possibly substitute CAN in this post with Ethernet.