"""They work like a check valve in that they have a rubber flap that opens to let air out if pressure builds inside the cabin enough to kick the flap up. But the flap keeps any dust, water, etc. from coming into the cabin from outside. Not real complicated, simple, but I don't see any reason anyone would want to block these off. ""
I torn out my interior plastic panels and blocked those 2 vents, they are mounted behind the rear wheels inside the wheel wells.
I have a really bad dust problem when driving down desert or mountain roads, everything in the rear area was getting covered in dust, blocking those rubber flap vents in the wheel wells dramatically reduced the dust problem.
poor design on the placement of those vents, they are designed to open up when the vehicle is moving, and being located behind the rear wheels, a lot of the road dust kicked up by the tires comes directly inside the vehicle thru these vents.
~Lewis