Cadillac 20852979 Mirror Assembly, Outside Rear View *Service Primer

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Most electric rear view mirrors use two motors to move the glass; one for up-and-down adjustments and one for left-to-right adjustments. In addition, some models have electrically-heated glass defroster circuits, which are usually powered through the rear window defogger relay. The control switch usually has a selector portion that sends voltage to the left or right side mirror. With the ignition ON but 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. If the mirrors don't operate and no sound comes from the mirrors, check the fuse. If the fuse is OK, remove the mirror control switch from its mounting without disconnecting the wires attached to it. On models where the power mirror switch is in the instrument panel, remove the switch from the instrument panel to probe the wires behind it. On models where the switch is in the driver's armrest, just pull up the switch panel. Turn the ignition ON and check for voltage at the switch. There should be voltage at one terminal. If there's no voltage at the switch, check for an open or short in the wiring between the fuse panel and the switch. Locate the wire going from the switch to ground. Leaving the switch connected, connect a jumper wire between this wire and ground. If the mirror works normally with this wire in place, repair the faulty ground connection. If the mirror still doesn't work, remove the cover and check the wires at the mirror for voltage with a test light. Check with ignition ON and the mirror selector switch on the appropriate side. Operate the mirror switch in all its positions. There should be voltage at one of the switch-to-mirror wires in each switch position (except the neutral "off" position). If there's no voltage in any switch position, check the wiring 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 fails this test.

Start by disconnecting the negative cable from the battery.