The FSU isn't just an E53 failure point, the E38 and E39 have the same exact problem. When I bought my 540i Touring with 176k miles it needed an FSU really badly because the fan would literally run at max speed and it would turn the car into a refrigerator. Funnily enough the old FSU was from 2004, so it had already been replaced once before (the 540i is a 1999 build). According to the Carfax, my X5 4.6 also had the FSU replaced at the dealership at 80k miles in 2009.

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2003 X5 4.6 | 2000 540i Touring

Formerly owned:
2004 Range Rover | 2000 M5 | 2000 540i/6
1995 750il | 2003 Mercedes S500 | 2003 540i/6