Actually, I have the unit un-potted and found two MOSFETs, a single IC and quite a few SMD discrete components. It could be a PWM, but so far I can not find a datasheet on the component. I also found several BMW forums that had un-potted their failed fan controllers as well. Same component IC and part number. They are clueless as to it's specifics as well and have not been able to create a proper schematic.

I will be tracing all the components and reverse engineering a schematic during the week. More to come... stay tuned!