Abstract: An undercarriage carwash system for use in a self-serve carwash bay includes a housing, a conduit with a plurality of nozzles, and a control. The bay has a support surface at which a vehicle is parked during the washing of the vehicle, and has a pressurized fluid system for discharging pressurized fluid via at least one spraying device of the bay to wash the vehicle. The housing is positioned on the support surface of the bay and entirely above the plane of the support surface. The conduit is positioned within the housing and is connected to the pressurized fluid system of the carwash bay. The nozzles are directed to discharge fluid from the pressurized fluid system of the carwash bay to an underside of a vehicle at the support surface of the bay. The control selectively provides pressurized fluid to the conduit for discharging the fluid by said nozzles.