a method and system for detecting the presence of a carrier mounted on the rear of a motor vehicle or of an object carried by the carrier that may cause damage or a malfunction of a rear wiper system of the motor vehicle . if a potentially obstructing situation is determined to be present , the rear wiper system is deactivated to prevent it malfunctioning or being damaged by the obstruction . a user of the vehicle may be provided with a message that an obstruction has been detected and the user may control whether the wiper system is deactivated . the obstruction may be sensed by monitoring the amount of current drawn by a wiper motor , by an ultrasonic sensor , or by a rear - view camera .