CPU Fan Error Diagnostic
Determining if the CPU fan is defective
To prevent any overheating or damage to the CPU, you want to rule out the possibility of a failed fan as quickly as you can. While the system is running, possibly stuck at the CPU Fan error, you can remove the left side panel (when looking at the front of the case) by removing 2 small screws in the back of the case that hold your side panel. For detailed instructions, refer to your case manufacturers’ manual.
CPU fan is the central fan of the system. It is usually large, ranging between 80mm to 120mm. In some cases of aftermarket heatsinks or dual processors, they may be 2 or more fans that are labeled as CPU fans.
Your first clue would be to see if the fan is actually spinning. If it does spin, then the error is most likely false, and can be adjusted in the motherboard BIOS to prevent it from coming back up. If the fan does not spin, or it spins just barely, DO NOT CONTINUE TO USE YOUR COMPUTER. Doing so, may damage the processor from excessive overheating. Although most today’s motherboards have a safeguard in place that will shut the system down in case of excessive temperatures, it is still a bad idea to allow your CPU to even get there.
If you or someone else built the system for you, you will need to contact the manufacturer of the fan/heatsink to obtain replacement if it’s still under warranty, or purchase a new fan or heatsink. We at AVADirect provide assistance and guidance to our customers over phone, email or other preferred method of communications on how to perform these repairs themselves or simply have them done by our RMA staff. If you did not purchase your computer system from AVADirect, it’s possible that your manufacturer or system builder might be able to provide similar assistance with this problem.
What to do if the fan spins normally
If the fan spins fine, the next step is to find out exactly how fast it is spinning. Most fans range between 400RPM – 2500RPM. If your fan is spinning less than 400RPM, then it might indicate that it will be failing soon and should be replaced. Unless you have a dedicated fan control module in place, your fan should be usually in the range stated above.
You can obtain the speed information couple of different ways. Motherboard BIOS usually contains hardware information such as temperatures, voltages and fan speeds. Please refer to your manual for how to access BIOS on your system as well as find the information about fans. Usually they are located in a section called Monitor, Hardware Monitor, Health Status and similar.
Once you find the CPU Fan speed, and it reports the RPM somewhere in the 400-2500 range, then this means the fan is actually healthy and the trigger is probably coming from a low threshold of the motherboard’s alert system. If the CPU is significantly below range, for example 50-100RPM, then it should be replaced.
If your fan is running OK, but the board continues to report CPU Fan error, then the issue is most likely with the threshold setting of the “Low RPM” limit value. Most motherboards, Asus in particular, like to leave the Low RPM limit setting on 600RPM by default, when the fan control module is enabled.
The issue with this is that many fans out there during startup may only spin up to about 400-500RPM, and then pick up their speed later. The board will notice the difference and give you the error.
Therefore, in order to remedy the problem, you will need to adjust the limit down to something like 200-300RPM. This will help avoid the error message, while at the same time keep the system in place should the fan really begin to fail in the future.
To change this setting on an Asus board you must go into BIOS by pressing DEL key. Fan control is located in the Monitor section of the board. The item in question is usually referred to as CPU Low RPM Limit, and you will see the default speed of about 600RPM. Change this speed to 200-300rpm and press F10 to save and exit.
The error should no longer come up provided that the fan is actually healthy which you proved in the earlier steps in this guide.
Once you’ve changed the limit, the issue is gone. You’re all set. No need to panic as this was not an actual problem, but rather a discrepancy between what motherboard manufacturers consider a reasonable low limit, and how the fans are manufactured. Bottom line is that if your fan spins at healthy speeds, these errors are nothing but annoyance, so turning them off is the right thing to do. But, keeping them active is a good idea just in case of actual failures. While you can disable them altogether, we still recommend 200rpm as the best setting because it will continue to be a failsafe should the fan actually fail.
*Disclaimer: AVADirect and its Staff are not responsible for any damage to software/hardware, loss of data or personal injury by following our How-To guides. These guides are provided only as an aid to help you troubleshoot system problems. If you do not feel comfortable performing these steps its always best to send in your system to a local repair shop or contact an appropriate technical support line for additional assistance.