I had this problem, only it was the drivers side rear window. I tested the door switches for continuity, (front and back) while it was not working and found them to test good. Then tested for voltage all the way to that door window motor. Voltage at the motor, but no joy. I removed the motor and disassembled it, cleaned the comm and reassembled it. It then worked fantastic, and has been for about 8 months now. I think it has to be lack of use on these windows and the comms get oxidized. Just running them once a month should keep them clean. Hope this helps.