All x5's were may 99MY or higher, they are all equipped with a Final Stage Unit controled by a control module, and this control unit is controled by pulse width from the Engine Control Unit. There were several re-calls on early bmws for these catching on fire. On every startup, The DME checks the operation of the Aux fan by sending a signal to the Control unit to turn the fan on momentarily. It then reverses the signal line into a listening line to measure the amount of amperage being generated by the fan as its moving. The aux fan should operate at 10hz when the temperature is 120°C