"I've been stranded on the road a couple of times in my old clunker, so I have some idea what that's like. Of course, I didn't have any control over any of the systems in my own car, so if my test vehicle dies, maybe I am further ahead than usual! If I'm lucky, the car died in a place where I can get it far enough off the road for me to safely check out a few obvious things. Maybe I can read the diagnostic codes to get some idea what might be wrong. I mean, fuel, air, spark, right? Which one am I not getting? Of course, I know that it is more complicated than that now, but that's a way to organize my thinking. I would ask myself what has changed on the car. Is there any new hardware? If I didn't install any, maybe someone else did. I would call back to the garage technician and ask. If I could identify any changes that might cause the car to quit running, I would check and see if a wire fell off somewhere. I'd ask myself if the software changes I had made could have caused this problem. Hopefully, the answer is no, because hopefully I tested the software on a bench before I put it in the vehicle. But I can't exclude this possibility. If the car isn't completely dead, if I get battery power when I turn the ignition on, then I would try to reinstall the last known good software, see if that helps. I don't like to admit defeat, but the wisest thing to do may just be to call the towing company and go back and deal with the problem at the lab or garage."