It’s unlikely but possible for an over the airway connection to actually be inherently secure. One example is an isolated system that could monitor say engine temperatures and oil pressure and nothing else.
Most are. GM OnStar systems & Tesla I know for sure are designed in a way that a malicious hack of HQ computers + research into car firmware could lead to a push that would kill potentially millions of people simultaneously. If I really dived into the others, I wouldn't be surprised if ford, VW, toyota and others had similar system design issues.
We are just lucky we live in a world where even 'hackers' don't go that low. I hope future regulation will mandate remote access airgaps. I don't think it's a big price to pay for non-entertainment / GPS software updates to require a physical connection
