well check for corrosion around the wiring, if that's ok, turn the PDC on and touch the sensor and see if you can feel the sonar, if that's ok it's probably the module

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2006 BMW X5 4.8is Lemans Blue/Beige/Dark Maple
-Nav, Comfort Seats, Heated Steering Wheel,
Rear Airbags, AUX Input
2009 BMW M3 Space Grey/Black/Carbon
-all options