Rear Object Sensors
WARNING: This page is about a different car, the 2013 Chevrolet Spark. However, it is still accessible from the selected car via links, so may be relevant.
The Rear Object Sensors are located in the rear bumper of the vehicle. The sensors are used to determine the distance between an object and the bumper. Each sensor emits an ultrasonic frequency which is reflected off any object located in front of or behind the vehicle. These reflections are received by the sensors. The time difference between the emission of the frequency and when the reflection is received is known as sensor ring time, it is used to determine the distance to the object. The sensors report this information to the Rear Parking Assist Control Module.