While driving last evening at a fairly high rate of speed my car went over a small bump around a manhole cover on the newly paved road I was on. The bump was not very jarring but a few seconds later I heard a loud rubbing sound and pulled over. A large black plastic piece directly behind the front air dam had come loose and I was able to remove it from under the car. What is this piece? It looks like some kind of cover. Secondly, is this going to be expensive to fix? TIA for your help!