I've been researching this very problem...the fan will not respond to the signal sent from the dme.
Simply put is that fan has an internal component (second stage unit) im sure it can be repaired but with all the trouble one would have to go through, best to simply purchase another fan. Fans are not cheap$$$. Aftermarket fans are hit or miss...I'm sending one back today ($187). I read a lot of posts, general solution...purchase new fan!
I've even tried the boneyard, no luck there -for me-. I've inquired at an electrical repair shop...they were familiar but they informed me the parts can't be purchased and is unique only to bmw.
Haven't called the dealer yet..
we know whats there$$$$!
However, I could inquire with the indy repair shops.

My e83 has been down for a month now...with work and no time for experiments and trials, ive got to bite the bullet....$280 plus bucks...however, I take solace in the fact I've been meeting the bmw repair challenges over the last 6 years successfully. I've saved a considerable amount of money on my own ingenuity.