The application for the car wash here was actually recommended for approval, and the committee still turned it down. So don't be too despondent just yet.
If they don't have permission, you can contact the council on Monday and report that they're operating a car wash without change of use permission, they will then need to send out a planning enforcement officer.
If they wish to continue operating as a car wash, they will need to apply for permission, at which point you and your neighbours need to start putting forward objections. A petition and letters are the way to go, also get your local councillors on board.
In fact, if I were you I'd be getting a phone number for one of your ward councillors and calling them today to ask if they are aware of the car wash and any change of use application (they should be aware of any applications in their ward).
A long shot also, is there any wildlife nearby? One of the grounds the neighbours of our pub used in their objection was newts nesting in their garden. Other reasons for objections are obviously noise (machinery and shouting/car noise), waste water run off and traffic.
I'm happy to help you in any way I can based on how we stopped the application for the pub near us. PM if you want to :)