it is the alternator for sure. i already posted what happened when my wife was driving home and all of the suddent everything went dead but ABS, Faisafe, battery symbols all lit up. she was too scared to continue driving it, she pulled off the shoulder and it couldnt start again. i went to the dealer and had them estimated the cost of replacing the alternator, it was $1200. i decided not to have it replaced, i went to another dealer and they estimated $850, i still thought it was too much for just the alternator. went home bought from pepboy for $200 and have the local indy shop did it for $180 including 2 belts, alternator belt and ac belt. done. the x started fine again and drive like a champ. good luck.

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2002 X5 3.0 Siena Red
Premium, Cold Weather, Rear Climate Packages, 19" Wheels
Aluminum Running Boards, Clear Tail Lights, Clear Side Markers
Titanium Kidney Grills, Titanium Trunk Lid, Xenon Headlights
4.6is X5 exhausts, 35% Tint, Aluminum Pedals
2005 530I Mystic Blue
Premium Package, Sport Package, Xenon Headlights
18" Sport Wheels, 35% Tint all around
Mods to come: M-Tech Front Bumper, M5 Side Skirts, M5 Rear Bumper
Quad Exhausts, Style 172 19" Wheels