Ask Joe Mechanic - Rear Parking Assist

Rear parking assist is a feature that has been around for about ten to twelve years on select higher end vehicles and slowly became more popular on many SUVs and other vehicles.  However, back-up cameras are gradually replacing it. The system is designed to give warning of any object behind the vehicle while the car is backing up, and to give a more frequent warning as that object is being approached.  There are basically two types of systems in use. Both are considered proximity sensors, which will give off an audible and sometimes a visible warning while backing up. The two types are either electromagnetic or ultrasonic sensors.

            Ultrasonic proximity sensors are the more common of the two types and also the most recognizable. These systems usually have about four or five approximately one-inch diameter round sensors installed in the rear bumper cover. These sensors detect the distance between the object and the sensor by emitting acoustic pulses. A control unit measures the return interval of each reflected signal and calculates the distance. The system then warns the driver by emitting an audible tone inside the passenger cabin with the frequency of the tone signaling the distance. It emits a faster tone as the vehicle approaches the object until as it is very near it will emit a continuous tone.  Some vehicles have incorporated an LED or LCD indicator to provide a visible as well as the audible warning. A portion of the newer vehicles using this system even show the location and size of the object as a colored block on the vehicles’ infotainment system.

           

Generally, rear sensors are automatically activated when the vehicle is placed in reverse. One drawback of ultrasonic systems is that they rely on the reflection of sound waves, which may not be reflected off a flat object or a flat object that is set at an angle that prevents the return signal from reaching the sensor. The other drawback that I have personally witnessed is the pickup of false readings from heavy rainfall. A third, but minor drawback is that this type of sensor must be externally mounted, usually in the bumper fascia.

Mauro Del Signore patented electromagnetic parking sensor systems in 1992. These sensors rely on the vehicle moving slowly and smoothly toward the object to be detected. Once noticed, the signal will continue even if the vehicle stops moving. Once the vehicle resumes motion, the signal will become more frequent and intense until the vehicle stops moving and changes direction. The advantage to this system is that it can be mounted on the inside of the rear bumper without requiring any holes to be drilled or the cover to be defaced. It is also now possible to order a camera to work in conjunction with this system.

Next week we will cover backup cameras and blind spot monitors as these two systems utilize the same technology.  Some information for this article was sourced from Wikipedia.org.