I have an 04 X5 also and the same problem. My light came on about 3 weeks ago. I looked at AutoEnginuity and had a little sticker shock. The scan tool is $249.95 and then you have to get the BMW specific software for an extra $229.95. After searching around I found Bavarian Technic for $287.

The Technic includes hardware where one side connects to the car and the other end connects to a PC to run the software. It is a good deal if you have access to a laptop or can move your computer to be near the car.

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[Sold] 2004 X5 4.4i - Sterling Gray - Truffle Brown, Sport, Preminum, Rear Climate, DSP, Sirius, PDC, 132's (19 inch wheel), Comfort Seats
Dynavin, JL Audio Stealthbox, Alpine PDX-5 Amp