Rear Object Alarm Sensors
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 object alarm 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 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 echo time, it is used to determine the distance to the object. The sensors report this information to the parking assist control module.