Ok, I know this isn't the original thread (Asus Matrix GTX580 - PWM Fans Won't Turn Off) , but I was not allowed to post further there?!
[*]
'Sie sind nicht angemeldet' is the message.... well thankyou.
[*]
Anyway, thanks 'hrmes' , I had not heard of that, but it fits with what is happening. I can only think that PWM has problems controlling the fans at low rpm, ie they have to have 20%+ duty cycle to work properly.
[*]It would certainly explain what is happening.
[*]In light of all that, hrmes request in the original post ...' If fan channel 4 is in PWM mode and is given a fan speed value of 0 then turn off the 12V line. Could this be done Shoggy ? '
[*]is the only possible solution.
[*]2 other things:
[*]Shoggys reply indicated that he, unfortunately, hadn't understod the question.
[*]Hrmes idea ('Aquaero sets the +12V line to 0V when the lower limit reached') MUST be implemented by AC, at least if they want the PWM channel to be anything else than a marketing ploy.

Well it's a hack alright, but don't see why it wouldn't work - not for me tho' 'cos I'm using all 4.

The PWM 50% rotation works fine for me, but only if the 'Minimum Fan Power' is set to zero in the Fans Tab Settings. For some reason a positive MFP here will cause a 2/3 percentage when it should be 1/2.

I agree, what is the point of a fan, specifically designed to save power at low rotations, that will not turn off?!? I thought it was an Asus 'safety feature' or something for their graphic card fan, but if it's universal then maybe there's a technical reason that makes PWM unreliable between 0-20%. But it cannot be unreliable at 0%, so it is really up to AC to cough up a firmware alteration that solves this - it could be made as an option at least.

Sorry about the late reply - never noticed.