I have had this happen with 2 different doors (Drivers and rear). It is the power lock control unit. I don't know what happens to it, mine just stopped working in the rear door case. For the drivers door it broke because it was slimjimmed (don't ask).

The unit costs less than $100 (make sure you get the right one for the right side). Pretty easy to fix, just pull off the door panel undo the two hex bolts that hold it in and unplug the two power cables that go to it. You will then have to unbolt the interior handle to remove/replace the cable as it is attached to the power lock unit. The hardest part is physically wiggling the unit out. For the rear door I had to loosen the window channel to get it out.

Not a bad job at all in my estimation.

db