Ditto upallnight..the variable speed aux fan used after 9/1998-up (like in the M54/M52TU/M62TU/M57/M57N/N62) is controlled by the ECU/ECM/DME which sends a PWM signal to the aux fan to turn on under specific circumstances (approx 4-5 criteria).

The aux fan is not like the 2 & 3 stage aux fans used in earlier BMW models with the M62/M52/M50/M30 engines.

And at start up...the aux fan will turn on briefly as a test for the DME to know that the aux fan is okay:

__________________
Become a BMW CCA member! Click HERE to join and feel free to use my BMW CCA member #191509 as a referral.

• 2015 f06 650ix GC (Moonstone exterior/Cohiba brown Merino Leather interior)
• 2014 f15 X5 50i (Space Gray exterior/Mocha Nappa Leather interior)