Car chasing is one of those behaviors that you see in movies and cartoons, but don't really think that dogs do it in real life. Unfortunately they do, and most that do actually chase cars don't live very long.
This is one of those things where using aversion therapy is just as dangerous as the behavior, since you would have to let him start to chase the car before attempting to turn him off of it. You really need to stop it altogether, by removing his ability to chase completely.
Dogs that chase cars should never be allowed off-leash. It really is that simple. If your dog is not under your complete voice control, he should be allowed loose unless he is a secure, dog-proof arena, like a dog park, or fenced-in yard.
