I highly doubt that you'd be able to shoot a thief who is stealing someone else's car without receiving any negative legal repercussions. Heres how I see the law: If you use unreasonable and unnecessary force to stop or detain a burglar (or any criminal for that matter) you can be charged criminally and held civilly liable (i.e. he could sue you). What gets classified as "unreasonable and unnecessary" is in the hands of a jury and frankly, I wouldn't want my future in the hands of a jury.
However, the story changes if your life is in potential danger (i.e. a thief breaking and entering into your home or place of dwelling) because you can argue self defense in court. But then again, that doesn't eliminate the possibility of the thief still sueing you as seen here.
Burglar pursues suit against doctor who shot him | The Janesville Gazette | Janesville, Wisconsin, USA
Look up Joe Horn, he did it. DA didn't even try to prosecute.