Brap84
The heated mirror is usually what fails. Befor replacing it, remove the mirror and check for corroded contacts. Operate the mirror such that it is at a severe angle to let your fingers get in behind it. Pull the mirror straight out. It is held to the motor mount by four plastic tabs. Some force may be required. If after cleaning and re-seating the contacts the problem persists. Purchase a new heated mirror from the dealership. The are not expensive and install by now straighting out the angle of the motor and simply snapping in the new mirror applying equal force to all four corners of the mirror.