A CPU fan speed detection error is a common issue that many PC users see when turning on their computer. This error usually appears on the BIOS screen before the operating system loads. It tells you that the system cannot detect proper fan speed from the CPU fan header. While sometimes it can be a small issue like wrong connections, other times it can mean serious cooling problems. In this guide, we will explain causes, solutions, and advanced fixes step by step.
Causes of CPU Fan Speed Detection Error
This error can appear for several reasons. The most common cause is that the CPU fan is not connected to the correct header on the motherboard. Many motherboards expect a signal from the CPU_FAN header, and if they do not get it, they throw an error. Another cause is when the fan spins too slowly (low RPM) or when an AIO cooler pump is connected but does not send a signal. BIOS misconfiguration, outdated firmware, or even a faulty fan header can also trigger the error.
CPU Fan Speed Detection Error AIO
If you are using an AIO (All-in-One) liquid cooler, you may often see this error. This happens because many AIO pumps are designed to connect to the AIO_PUMP header, not the CPU_FAN header. If the CPU_FAN header does not detect a spinning fan, the BIOS will assume there is no cooling and will stop the boot. The solution is to connect one of your radiator fans to the CPU_FAN header or adjust BIOS fan monitoring. Also, make sure the pump is powered properly from the right header or SATA connector.
CPU Fan Speed Detection Error ASUS / ASUS AIO
ASUS motherboards are known for showing this error frequently. ASUS BIOS has strong monitoring features, and if the CPU_FAN header is not used correctly, the error appears. For ASUS AIO users, the best way is to connect at least one radiator fan to CPU_FAN, while connecting the pump to AIO_PUMP. In ASUS ROG, Z790, and B650 boards, you can also go into BIOS > Monitor > Q-Fan settings and disable CPU fan speed monitoring or set it to “Ignore” if you know the cooler is working.
CPU Fan Speed Detection Error Corsair AIO
Corsair AIO coolers use special connectors and often rely on the iCUE software for full monitoring. However, the motherboard BIOS still needs to see a signal. If you only connect the pump through USB or SATA without plugging anything into CPU_FAN, you may get the error. The fix is to connect one Corsair fan cable to CPU_FAN or use a splitter. Some users also report that setting the BIOS monitoring to “Ignore” removes the error safely when the pump is connected properly.
CPU Fan Speed Detection Error BIOS / AMI / AMIBIOS
BIOS is responsible for checking fan speeds at startup. AMI BIOS and AMIBIOS systems often display “CPU Fan Speed Error” if no RPM signal is detected. In these cases, entering BIOS and adjusting the fan monitoring settings is the key. You can also reset BIOS to default settings or update to the latest version. Some motherboards have advanced options where you can select the minimum RPM level for the CPU fan. Lowering this limit can stop false errors.
CPU Fan Speed Detection Error After BIOS Update
Sometimes, after a BIOS update, users see this error for the first time. This happens because the update may reset fan monitoring to default, expecting a CPU fan signal. If you use an AIO pump, the settings may not match anymore. To fix this, you should re-enter BIOS, check the fan configuration, and set the correct headers. In rare cases, reflashing or downgrading the BIOS might be required if the update caused bugs.
CPU Fan Speed Detection Error Ignore / Set to Ignore
Most BIOS systems have an option to “Ignore” the CPU fan speed error. This can be useful when using AIO pumps or non-standard cooling systems. To do this, you enter BIOS > Monitor > CPU Fan Speed and set it to Ignore. However, this should be done carefully. Ignoring the error means your system will not warn you if the fan actually fails. Use this only if you are 100% sure that your cooling system is working properly.
How to Fix CPU Fan Speed Detection Error
Here is a step-by-step fix:
- Turn off the PC and check if the CPU fan or AIO pump is connected to the right header.
- Connect at least one fan to CPU_FAN header.
- Enter BIOS and check monitoring settings.
- Adjust Q-Fan or fan control to match your cooler type.
- Update BIOS if the issue started after hardware upgrades.
- Replace cables or fans if faulty.
- As a last option, set fan monitoring to “Ignore” if using AIO.
Community Insights (Reddit & Forums)
On Reddit and other forums, many PC builders report this error, especially with ASUS and Corsair AIO coolers. The most common solution shared is connecting at least one fan to CPU_FAN even if the pump is on AIO_PUMP. Some users also recommend BIOS updates or simply setting the option to Ignore. The main mistake people make is ignoring the error without checking cooling first, which can cause overheating.
Best Practices to Prevent CPU Fan Errors
To prevent this problem in the future, always connect the cooling system correctly during installation. Check your motherboard manual for CPU_FAN and AIO_PUMP headers. Keep BIOS updated and review fan monitoring after updates. Regularly clean fans and ensure they spin freely. Using reliable brands for AIO and fans also reduces the chance of detection errors.
Conclusion
CPU Fan Speed Detection Error is a common but fixable problem. Most of the time, it is caused by wrong connections or BIOS settings, especially with AIO coolers. The key is to make sure the CPU_FAN header always gets a signal. If everything is working but the error still shows, using the Ignore option in BIOS is safe. However, never ignore the risk of overheating. Proper installation, regular monitoring, and updated BIOS are the best ways to keep your system safe.
FAQs on CPU Fan Speed Detection Error
What causes CPU Fan Speed Detection Error?
It happens when the BIOS does not detect a proper signal from the CPU fan header, often due to wrong connections or low RPM.
How do I fix CPU fan error on ASUS BIOS?
Connect one fan to CPU_FAN, put the pump on AIO_PUMP, and adjust Q-Fan settings in ASUS BIOS.
Can I ignore CPU fan speed detection error safely?
Yes, if your cooler is working properly and you are sure the pump or fans are powered, you can set the error to Ignore.
Why does my AIO cooler cause this error?
Because many AIO pumps do not send RPM signals to CPU_FAN, leaving the BIOS to think no cooling exists.
Does BIOS update affect fan detection?
Yes, BIOS updates may reset monitoring settings, which can trigger the error even if the cooler is fine.