Air Fan Won't Switch Off Even With Engine Off

[X50 LFC]

Hi there, I recently bought an X5 Jan 02 and the day I drove it home the fan stopped working. I took the motor to a BMW Service/Showroom for a service and to sort the fan problem. Im was told the AUC sensor was flagged up as faulty - they found it had become disconnected? They plugged it back in but still no fan opperation. Then they managed to get a hand to the fan and told me they had manually freed it off and it started working again.

Last week it just stopped again - they tell me it may need a new fan - £575 to replace as it means taking out the full dash.

This morning whilst driving it came back on in full force and will not switch off with the controls or even when I shut the engine off and remove the key.

I have had to disconnect the battery to save it being run down - is it a faulty resistor? I would like some experienced views on the problem before I let a so called expert charge me hundreds of pounds to replace a perfectly good fan.

Thanks in advance to anyone who can shed any light on the matter.

Carl