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BIOS "CPU fan error" message on a two-week-old gaming build

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March 3, 2012 5:16:37 PM

I'm a novice builder, and I've got my brand-spanking-new gaming machine up and running really well...almost. Several days ago when I booted up, I got an American Megatrends message ending with "CPU fan error! Press F1 to enter setup." So I hit F1, which took me to my Asus motherboard's BIOS and showed CPU temperature and fan speed readings that looked familiar from over the past week (~31 degrees C and 1100 RPM). Pulling off the side panel I could see that all the fans were spinning away just fine. I let it sit for a while and finished booting, and things seemed okay.

I downloaded RealTemp and SpeedFan to monitor my temperatures and fan speed within Windows. (One thing I noticed right away is that SpeedFan doesn't seem to report my "CPU temperature" correctly; most of the time it's pegged at -60 C and occasionally I see other wacko values like 124 C. The Core 0 - Core 3 temperature readings agree nicely with RealTemp and the BIOS, though.) I also googled around a bit, and saw opinions on this error ranging from "it's nothing, turn the warnings off" to "the CPU is about to melt." I'd like the Tom's community opinion on the subject.

The first time I got the error, I reset the motherboard CMOS memory and the issue went away. I monitored temperatures while gaming a few times and they seemed consistently south of 55 C. However, I just saw the American Megatrends message appear again, same as before. The temperature trends seem to be fine, again - about 50-55 with ~60% CPU load, and then cooling down to under 35 C pretty quickly when the load dropped to a few percent.



After all that, I'm leaning towards the "ignore it" solution. But this build is very new and I want to make sure I clear out any serious bugs. Would I be right to disable the CPU fan alarms? Or are there other optimal alarm settings for my system?

My computer:
  • Motherboard: ASUS P8Z68-V PRO/GEN3
  • CPU: Intel Core i5-2500K (stock Intel cooler plugged into CPU_FAN)
  • Case: Antec Three Hundred Illusion Black Steel (four fans, plugged into CPU_FAN_OPT, PWR_FAN1, PWR_FAN2, and CHA_FAN2)
  • Power: COOLER MASTER Silent Pro M700 RS-700-AMBA-D3 700W
  • Graphics: Sapphire Radeon 7950
  • RAM: G.SKILL Ripjaws F3-12800CL9D-8GBRL 4GB 1600 x2
  • Optical Drive: Samsung SH-222AB CD/DVD Burner
  • Storage Drive: Western Digital Caviar Black WD1001FALS 1TB (x2 in RAID1)
  • System Drive: Crucial M4 CT064M4SSD2 Solid State 64GB

    In general I'm fantastically happy with this thing...it seems to eat Skyrim for breakfast all while cool air blows out of the case. Silently. I would just like to make sure I'm not about to kill my CPU!

    Thanks, everyone!
    a b B Homebuilt system
    a b 4 Gaming
    a c 97 à CPUs
    March 3, 2012 7:05:31 PM

    Make sure that the CPU heatsink fan is plugged into the CPU_FAN header on the motherboard. After that is checked, physically observe the CPU heatsink fan for any faulty rotation.

    If the fan is defective, you could see temp fluctuations based on intermittent fan operation.
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    March 3, 2012 7:22:36 PM

    Ubrales said:
    Make sure that the CPU heatsink fan is plugged into the CPU_FAN header on the motherboard. After that is checked, physically observe the CPU heatsink fan for any faulty rotation.

    Okay, to clarify, yes the CPU fan is connected to CPU_FAN on the motherboard. I can't see any obvious "faulty rotation" - it's spinning, fast, and appears to be rotating smoothly.

    If the fan is defective, you could see temp fluctuations based on intermittent fan operation. said:
    If the fan is defective, you could see temp fluctuations based on intermittent fan operation.

    What do you mean by "intermittent fan operation?" Like...stopping and starting, or variable-speed operation? I am looking at my temperature vs time charts, and I see occasional singleton data points that spike up (you can see it in the picture above, towards the end of the trace). That looks to me like it's just sensor noise spikes, but are you saying it could be a sign my fan is defective?
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    a b B Homebuilt system
    a b 4 Gaming
    a c 97 à CPUs
    March 3, 2012 7:36:07 PM

    perinigricon said:
    ...... What do you mean by "intermittent fan operation?" Like...stopping and starting, or variable-speed operation? I am looking at my temperature vs time charts, and I see occasional singleton data points that spike up (you can see it in the picture above, towards the end of the trace). That looks to me like it's just sensor noise spikes, but are you saying it could be a sign my fan is defective?

    Yes, intermittent problems are the most difficult to solve because when you are looking at it, the fan seems to be operational and spinning.

    Check the CPU_FAN setting in the BIOS. It may be set to a high CPU temp. - change this if necessary and then check the performance.
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    March 3, 2012 8:09:36 PM

    Mine started to do it occasionally as well - its coz it getting old and I think it just not start up as quickly as it used to
    (and at my age... I know that feeling!!! :ouch:  ) so the BIOS pops up the warning.
    By the time I check it ... its spinning just fine.

    Ill replace it when I next passing my local PC shop.

    Cheers
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    March 3, 2012 8:55:04 PM

    Ubrales said:
    Yes, intermittent problems are the most difficult to solve because when you are looking at it, the fan seems to be operational and spinning.

    Yeah, that's why I wanted to look at graphs. :) 
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    a b 4 Gaming
    a c 126 à CPUs
    March 3, 2012 11:36:40 PM

    Have you updated the BIOS? That mobo (same as mine) comes with 0402 but they have 3202 out already.

    Try that and see if it helps as that sometimes solves a lot of issues.
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    March 4, 2012 2:48:26 AM

    Will do!

    Since you've got the same board, maybe you can comment on my latest theory: I realized that I had one of my big, slow fans connected to CPU_FAN_OPT, and it was running around 700 RPM. The CPU fan warning is set to 600 RPM (default). I thought the warning would only be triggered by CPU_FAN, but if the same limit applies to CPU_FAN_OPT, then maybe I was occasionally falling below the 600 RPM line on boot-up. I've already swapped around my fan connections just in case, leaving CPU_FAN_OPT empty.
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    a b B Homebuilt system
    a b 4 Gaming
    a c 97 à CPUs
    March 4, 2012 1:47:52 PM

    600 RPM is too slow for any fan. If you look at the RPM Vs CFM curve you will find that the air flow at low RPMs is disproportionately low. Set the default low RPM to around 1,000 RPM.
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    March 7, 2012 7:26:18 AM

    jimmysmitty said:
    Have you updated the BIOS? That mobo (same as mine) comes with 0402 but they have 3202 out already.

    Try that and see if it helps as that sometimes solves a lot of issues.


    Hi guys, I appologise if this is a thread hijack but i have the same motherboard and i just got the exact same fan warning. Jimmy would you mind explaining how to update the Bios?

    Also did you end up finding a fix.

    I have the same mobo and cpu except i have a coolermaster 212 evo on mine.

    Sorry for jack but it seems like my problem is exactly the same as yours. Hope yours is all fixed up!
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    March 7, 2012 8:32:36 PM

    So here's where I am, right now:

  • All my chassis fans came with speed switches. Since I'm not overclocking and am apparently not having temperature problems, I've left those at the manufacturer-recommended "low" settings.
  • I moved the fan connections on the motherboard around. Now CPU_FAN_OPT is the unoccupied one.
  • I updated the BIOS.

    So far, no CPU fan errors on boot...

    Here's how I updated the BIOS, mattheuu:

    1. Go here, select your OS, and download the BIOS update .rom file to a flash drive.
    2. With the flash drive inserted, boot your computer into BIOS.
    3. Go into the "Tool" tab and select "EZ Flash."
    4. Select the flash drive and .rom file and click through the update/OK buttons.
    5. Let your computer reboot itself. Remember to go into setup and fix any settings you changed (like SATA RAID configurations)!
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    !