66 20 537 Removing and installing/replacing a rear middle right ultrasonic transducer (Park Distance Control)
WARNING: This page is about a different car, the 2010 BMW X5, 2009 BMW X5, 2008 BMW X5, and 2007 BMW X5. However, it is still accessible from the selected car via links, so may be relevant.
Operation is described in: Removing and installing/replacing rear middle left ultrasonic transducer