the police can't impound your ride for "probable cause". if that happened, that woul be grounds for a lawsuit. you need to take a look at your 4th amendment right. the right against illegal search and seizure. now, if you are pulled over for a felony stop, like dui, going 150, something like that, then they can search whatever, whenever they want. you do have the right to refuse anything and your ride won't be impounded unless it's a dui stop. that's about the only stipulation.