The contact owns a 2016 GMC Sierra 1500. The contact stated that while driving at 20 MPH with the defroster engaged, she noticed smoke on the rear electric sliding glass window and smelled a burning odor. There were no warning lights illuminated. The contact veered to the side of the road, disengaged the defroster and the smoke gradually faded away. The contact continued to drive the vehicle. The contact notified the dealer of the failure and scheduled an appointment for diagnosis. The manufacturer was not notified of the failure. The vehicle was not diagnosed or repaired. The failure mileage was approximately 64,000.