Without saying you shouldn't rely on PDC/backup camera alone... I have to ask, you have the park distance control feature correct ? That is a separate option from the backup camera (even though you get both in the tech pkg). The PDC is the one that beeps. Also, did the camera display in the idrive at all?

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr