View Full Version : CPU Fan RPM problem

21-12-2010, 09:40 AM
I recently built my first computer, and everything worked brilliantly, with the exception of one issue -

For some reason, the computer is not properly reading my CPU fan RPMs. When looking at the indicator in BIOS, it seems like it will read the proper fan rpms for a few seconds, then will generate a nonsense number like 17,000 rpms (obviously wrong), or will simply read N/A. It will cycle through these 3 different readings every few seconds.

When booting the computer, when it checks for a cpu fan, and it just "happens" to be reading the correct rpm, the computer will boot with no problems. However, if during the fan check, it is getting the N/A or nonsense number, it will stop the booting process with a "CPU Fan Error, press F1 to Continue" message. Note, that I am NOT using the stock cpu fan.

Here is my build:
M4A89GTD PRO Motherboard
AMD Phenom II x4 955
Hawk Radeon HD 5770
WD Caviar Black 1TB
Arctic Cooling Freezer 7 Pro, v.2 CPU Fan
G.SKill Ripjaws 4GB
Corsair 750W Powersupply
Windows 7 64-bit

If anyone can give me some advice as to what is going on, that would be greatly appreciated. I'm not sure if it's a compatibility issue between the MB and the cpu fan, or if I simply bought a faulty fan or MB. Remember, this is my first build, and while I'm certainly computer literate, I'm by no means an expert. Thanks in advance for any input!

21-12-2010, 09:48 AM
Welcome to PressF1. You're right - it basically sounds like either the aftermarket fan just isn't sending the right signals to the motherboard, or the motherboard has an issue.

Have you double checked the fan is plugged in correctly? How many pins is the plug for the new fan? Same as the old one?

As long as you know the fan is spinning properly and the CPU temp is good, you should be able to disable the fan warning in the BIOS.

Do you still have your old fan around? Easiest way to diagnose weather it's a motherboard fault or a fan fault would be to plug in the old fan and see what the BIOS reads.

21-12-2010, 09:51 AM
maybe the aftermarket fan just wont work properly with your motherboard. Is it a 3 or 4 pin fan ? You could look in the BIOS for fan control settings like Q FAN or speed fan etc - it varies by brand - and disable the onboard speed control as it may be messing up with a non standard fan, this should make the fan run at full speed.

One Idea might be to plug a case fan into the CPU header to "fool" the BIOS and power your CPU fan from the case fan header or an adapter. The problem of course is the system wont be able to control the CPU fan speed correctly.

21-12-2010, 10:03 AM
Both the stock fan and the aftermarket fan are 4-pin fans, and believe me, I've checked and double-checked to make sure that it is seated properly. The asus board does have a "cool 'n quiet" fan monitoring application, not sure if that would cause the problem.

Couple questions based on your guy's responses:

- If I disable any kind of on-board fan control, will this make the cpu fan run at full rpm's at all times? Even with the rpm issue, I've never seen the cpu get over 41C, and that was during an extended time of gaming, so it's obviously doing its job.

- I do still have the stock fan. Are you suggesting plugging in the stock fan without actually mounting it on the cpu? Sorry if this seems like an ignorant question - like I said, i'm new to this. While this would immediately tell me whether its the fan or motherboard, it seems to me that would be a bit risky for the cpu.


21-12-2010, 10:19 AM
Doh, pushing escape apparently deletes everything you just typed!

anyway, plug the aftermarket fan into a case fan header or molex adaptor so the cpu is still being cooled then plug the stock fan or a case fan into the cpu fan header to see if it is recognised properly.

3 & 4 pin fans should plug into each others sockets and still work, the 4th wire is for PWM fan speed control but is not required to make the fan spin. (2 wires for power, 1 for RPM reporting and 1 for PWM speed control)

EDIT: cool & quiet also alters CPU clock and voltages dynamically so it's not just fan control. Yes disabling fan speed control will run CPU fan at full RPM, but it's worth trying as a test to see if the fan speed is read properly.

21-12-2010, 10:26 AM
Okay, thanks for the reply.

I will first attempt turning off all on-board fan control, and see what happens there. That is an easy and quick thing to do. Following that, i'll go ahead and attempt your suggestion with slaving in the cpu stock fan. I'll let you know how it goes.

21-12-2010, 10:42 AM
I'd update the BIOS first, shouldn't matter if it's 3rd party or not

21-12-2010, 10:45 AM
Well, I went into my BIOS settings, and sure enough, my motherboard had the asus "Q-Fan function," which, if I'm correct, monitors and regulates fan speed. I turned it off, and voila, it immediately started to give a consistent and correct reading of my fan rpms. Oh, and yeah, I already have updated the BIOS to its current version.

Of course, my fan is now running at a constant 2000 rpms, but it still generates hardly any noise, and since i use my comp mostly for gaming, having it constantly run at full speed certainly isn't a bad thing. I have no idea why the fan and the mb weren't able to "talk" to each other to regulate fan rpms. The fan I bought certainly isn't the newest one on the market (though it is still a very popular one, according to Newegg), so perhaps that is the reason.

Hopefully this provides a permanent fix for this issue. Thanks for all the help everyone. If anyone else has any more to add to this topic, feel free to post anyway!