Originally Posted by
pkellner
thanks. Someone already told me that earlier today. I wonder if having a hole like that should have something in it if I don’t have the sensor.
There is normally a rubber cover plugging the hole when there is no sensor is installed.
If this is a used bike then they may have removed the sensor to sell it separately and lost the cover.
You can buy this cover from Trek to close the hole if you do not intend to add a sensor.