Just opened up the panel inside the driver's wheel well, and saw the sensor wires had been cut. Actually, I believe that wear and vibration caused them to break. I removed the wheel, removed a few screws from the wheel well shroud, bent it up and back out of the way, and spliced the wires back together.

I was able to reach into the air duct enough to unplug the sensor connector, but I have no idea how I would have removed the sensor, if needed. I think I might have had to remove the bumper!

Anyway, the sensor is now working again. Thanks all!

Gary