I really can't imagine why that would ever happen. What car would ever use a clock for anything essential, instead of a timer? Maybe I'm overestimating the intelligence of car developers, but it seems like the obvious, simple solution.
Engine won't start, service due 300 years ago. I'd be willing to bet $10 there's at least a few floating around with real time clocks, no idea what they'd be used for though. If nothing else there's always in-car navigation and entertainment which are definitely candidates, although I suppose less likely to result in a brick.
I'm engaging in what is commonly known as using one's imagination to make educated guesses at the possible electronic devices within an average motor vehicle (you know, that thing with wheels on it) where a real time clock susceptible to wraparound or overflow might be found, thus resulting in potential malfunction, or in plainer words, "the car won't start, the tuner won't play music, the GPS won't get a signal, this thing is about as useful as a brick".
What car would ever use a clock for anything essential, instead of a timer?
You could say the same thing about the futex option that caused this issue in Linux in the first place. If the futex call specified a timeout in duration rather than an absolute time, this bug wouldn't have been hit (I observed the two different kinds of futex use during the leap second event).