MoovnOn

One of the ports on this transducer is labeled (in Mercedes service manual) "Air admission". The 2 inch rubber hose that connects to this port has a round plastic object at the other end, but this plastic object doesn't seem to connect to anything; it's simply open to ambient air. Does anyone know it this plastic part is supposed to connect to something?

I've attached a picture and the circle indicates the piece I'm asking about.