If the vent is working properly,,, and you bend down next to it, you should smell an aroma, if the conditions are right.
The next thing I would do is have someone flush a toilet, if the vent is within a few feet of the toilet ( like it's supposed to be )
You should be able to hear water flow,,,
So if you get an aroma and you hear water flow, the vent is working,,,
Then you have a different problem,,,