CPU Fan doesn't start on boot, eventually starts when CPU reaches 50degs or so. Same with 2 fans.

I have an Asus z97-M Plus motherboard. When booting from cold, I get a CPU fan error as the CPU fan doesn't run to start with. Eventually, once the CPU reaches about 50 to 53 degrees, it will spin up. After which I can boot normally. This takes about 5 to 10 mins. I assumed it was a problem with the fan, and bought a brand new Noctua PWM fan to swap out with - and to my surprise, I get identical behaviour. So I suppose the fans are fine!

The CPU fan profile checks out ok - it is set to run at 25% from zero degrees, and should be running over 50% by the time it reaches 45degrees or so. (the standard profile out of the box on this mobo).

Not sure if this helps, but this PC is a self-build, and behaved immaculately for some months before developing this issue. I'm not aware of any particular change made that coincided with this issue...

I can override the error in BIOS by telling the PC to ignore the CPU fan, but that doesn't seem sensible. And I don;t like not understanding these things.

Suggestions very welcome...

Reply to geoff1.nicholson
2 answers Last reply
More about cpu fan start boot eventually starts cpu reaches 50degs fans
  1. Are you positive your fan is plugged into the labelled "CPU FAN" header?
    Reply to Tyler Paul_1
  2. Yep. Checked that too.
    Reply to geoff1.nicholson
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