Rear Object Alarm Sensor
WARNING: This page is about a different car, the 2010 Buick LaCrosse. 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 rear bumper. Each sensor emits an ultrasonic frequency which is reflected off an object located behind the vehicle. These reflections are received by the sensors. The time difference between when the frequency was emitted and when the reflection is received, known as sensor echo time, is used to determine the distance to the object. The sensors report this information to the parking assist control module.