Nearly all the back mirror systems are hinged with two motors to shift the glass; one for vertical and the other for lateral movement. There is a control switch consisting of a selector portion connected to transmit voltage to either left or right sided mirror. While the ignition is on and the engine is off, open the windows and move through all functions of the mirror control switch for both left side and right side mirrors. The mirrors are also powered by electric motors whose sounds should be heard when they are operating. Should only the motors be audible while the mirror glass remains still, there is an issue with the drive mechanism within the mirror. If they do not work and there is no sound coming from them, whether they are the old manual ones that need a tiny coin to be pushed to get them work or the new automatic ones, look for the
Fuse. If the fuse is tested as good, the mirror control switch is next removed and the switch continuity should be taken to a dealership service department or a qualified automobile repair shop. Ensure that the mirror has been well earnd. If it is not working then attempt to disconnect the wires at the mirror and if there is voltage then the mirror has to be replaced. That is, if there is no voltage in each switch position, go around the circuit between mirror and control switch with an ohm meter and check for opens and shorts. If there is voltage present the mirror should be removed and testing done off the car with jumper leads and if faulty, it should be replaced.