My Hampton Bay ceiling fan (controlled by it's companion remote) isn't responding to the remote control commands. I changed the batteries in the remote, still no response. Is it possible that the sensor in the fan is dirty and is therefore causing this problem? Where is this sensor located?

Its RF or current carrier, not likely IR. If it is a handheld remote and not IR, their should be an antenna at the receiver, just a piece of wire.
The codes have to match.