WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View Of Rear Object Sensor
Courtesy of GENERAL MOTORS CORP.
Disconnect electrical from the rear object sensor.
Lift the locking tabs on the housing and remove the rear object sensor.