Whilst I hate to tell the factory they're wrong about something...
The ECU didn't control the fan until the "Black Top" Zetec or Focus engine was fitted in late 2001/early 2002
Chances are it's the otter switch (bottom right of the radiator) throwing a wobbler or as Colin pointed out, the relay may have fused in in its "on" position
Simon @ SiFab.co.uk