GMC 20873491 Mirror, Outside Rear View (Reflector Glass & Backing Plate)

These models are equipped with a Body Control Module (BCM). Several systems are linked to a centralized control module that allows simple and accurate troubleshooting, but only with a professional-grade scan tool. The Body Control Module governs the door locks, the power windows, the ignition lock and security system, the Interior lights, the Daytime Running Lights system, the hom, the windshield wipers, the heating/air conditioning system and the power mirrors. In the event of malfunction with this system, have the vehicle diagnosed by a dealership service department or other qualified automotive repair facility. The electric rear view mirrors use two motors to move the glass; one for up and down adjustments and one for left-right adjustments. The control switch has a selector portion which sends voltage to the left or right side mirror. With the Ignition in the ACC position and the engine OFF, roll down the windows and operate the mirror control switch through all functions (left-right and up-down) for both the left and right side mirrors. Listen carefully for the sound of the electric motors running In the mirrors. If the motors can be heard but the mirror glass doesn't move, there's probably a problem with the drive mechanism inside the mirror. Power mirrors have no user-serviceable parts Inside a defective mirror must be replaced as a unit. If the mirrors don't operate and no sound comes from the mirrors, check the fuses. If the fuses are OK, remove the mirror control switch. Have the switch continuity checked by a dealer service department or other qualified shop. Check the ground connections. If the mirror still doesn't work, remove the mirror and check the wires at the mirror for voltage. If there's not voltage in each switch position, check the circuit between the mirror and control switch for opens and shorts. If there's voltage, remove the mirror and test it off the vehicle with jumper wires. Replace the mirror if it falls this test.

If the mount plate has come off the windshield, you can use adhesive kits available at auto parts stores to resecure it. Follow the instructions included with the kit and make sure to position the flanged part of the mount away from the glass and the narrower part pointing up.