Same problem here, very inconsistent or doesn't work at all.
Picked up my 2014 X5 with active blind spot.
90% of the time no matter what speed, the passenger side doesn't flash at all. 50% of the time driver side will blind if the car is coming from behind, If I pass a car or a car merged into the lane next to me it would not flash.
i'm going to have the dealership look at it, coming from Mercedes and Toyota, they work 99% of the time and this just isn't right.
one more question... does the blind spot warning just flashing? does it suppose to have audible tone? beep? vibration? anything else beside the flashing light?
Thanks
still trying to learn everything about this car