I have a 2001 STS that has been in twice for the very same reason. I could be doing 60 miles an hour and the car will completely turn off - no power steering, no brakes etc .. or I could be idling at a light and it does the same thing. Sometimes it just quits with the power windows or dash lights. I heard some STS's were recalled because of this. I don't want to get rear-ended because the car shuts off. Can anyone advise me?