This guide covers the CPU Fan Error message (often followed by Press F1 to Run SETUP or Press F1 to Resume) displayed at startup, before Windows. It is issued by the motherboard during POST (the startup checks). According to ASUS, it means the motherboard does not detect the rotation speed of the processor fan. The fan may be badly connected, plugged into the wrong header, too slow to be detected, or absent because the processor is cooled by liquid cooling.
The steps below follow ASUS documentation. On motherboards from other brands, the BIOS menus often exist under similar names: check your motherboard manual for their exact names.
Problem
- CPU Fan Error message when the PC is switched on.
- Windows only starts after pressing F1, or the PC opens the BIOS directly.
- The problem often appeared after building the PC, changing the CPU cooler or liquid cooler, or cleaning the PC.
Before you start
- Note the exact motherboard model (on the board itself or in the BIOS) to find its manual on the manufacturer's website.
- Note the type of processor cooling: stock cooler, third-party cooler or liquid cooling.
- Before opening the case, shut down the PC and unplug the power cable.
| Observation | What to check |
|---|---|
| The processor fan doesn't spin | Step 1 |
| The fan spins but the message remains | Step 2 |
| Third-party cooler, slow or silent fan | Step 3 |
| Liquid cooling or no fan on the CPU_FAN header | Step 4 |
| The message appears after overclocking or a battery change | Special cases |
Step 1: check that the fan spins
When to use it: always first. If the processor fan doesn't spin, the message signals a real risk of overheating.
Suggested solution
- Open the side panel of the case (PC shut down and unplugged), then switch the PC on briefly while watching the fan mounted on the processor.
- If it doesn't spin, shut the PC down immediately.
- Check that no cable or dust build-up is blocking the blades.
- Check, as ASUS asks, that the fan is firmly fixed in place and that its screws are tight.
Expected result: the fan spins freely as soon as the PC is switched on. If it still doesn't spin once correctly connected (step 2), it is probably faulty and must be replaced.
Warning: don't use the PC while the processor fan isn't spinning. Don't disable the alert (step 4) in that case: it is there precisely to warn you.
Step 2: plug the cable into the CPU_FAN header
When to use it: if the fan spins but the message remains. ASUS states that the cable must be plugged into the CPU_FAN header and not into a CHA_FAN header (case fans).
Suggested solution
- With the PC shut down and unplugged, follow the processor fan cable to the motherboard.
- Find the label printed next to the header: it must be CPU_FAN (the exact name is in the motherboard manual).
- If the cable is plugged into CHA_FAN, SYS_FAN or a fan hub, reconnect it to CPU_FAN, pushing the plug in firmly.
- Switch the PC back on.
Expected result: the message no longer appears, and the BIOS shows a speed in RPM for the processor fan.
Step 3: adjust the detection threshold for a slow fan
When to use it: if you installed a third-party cooler, or a silent fan that spins slowly. According to ASUS, the motherboard may then fail to detect it correctly.
Suggested solution
- Switch on the PC and enter the BIOS (often with Del or F2 on ASUS boards).
- Switch to Advanced Mode if needed, then open Monitor (or your board's fan control tool).
- Set CPU Fan Speed Low Limit to 200 RPM.
- If the option doesn't appear, ASUS specifies that it is only visible when CPU Q-Fan Control is set to [DC Mode], [PWM Mode] or [Auto] (on older BIOS versions: [Enabled], [Advance Mode] or [Auto]).
- Save with F10 and restart.
Expected result: the fan is detected at low speed, and the message disappears.
Step 4: ignore the header speed if liquid cooling is installed
When to use it: only if the processor is cooled by liquid cooling whose pump or fans are connected elsewhere, or if no fan is meant to be on CPU_FAN. ASUS states that the option can then be set to [Ignore].
Suggested solution
- First check that the pump and fans of the liquid cooler work (speed shown in the BIOS, fans spinning).
- In the BIOS, open Monitor.
- Set CPU FAN Speed to [Ignore].
- Save with F10 and restart.
Expected result: the PC starts without the message, and you keep an eye on cooling yourself (normal temperatures in the BIOS).
Special cases
- The message comes with other errors (CMOS, overclocking): ASUS lists these cases in its page about pressing F1 at startup. A CMOS checksum error often points to a worn motherboard battery, and an overclocking failure requires going back to the BIOS default settings.
- Disabling the F1 wait: ASUS states that the Boot > Wait For 'F1' If Error option can be disabled, but the manufacturer doesn't recommend it: the error would then be hidden without being fixed.
- The message persists despite correct wiring and a spinning fan: as a last resort, ASUS suggests updating the BIOS using the manufacturer's method. Follow its procedure to the letter, without cutting the power during the operation.
- The PC runs hot or is very noisy: see PC qui chauffe trop et ventilateurs très bruyants (French guide).
Final check
- ☐ The processor fan spins as soon as the PC is switched on.
- ☐ Its cable is plugged into CPU_FAN.
- ☐ The BIOS shows a speed in RPM for the processor fan (or [Ignore] only with working liquid cooling).
- ☐ The PC boots to Windows without the message or pressing F1.
Sources
- ASUS: Why I see the error message "CPU FAN Error" in POST?
- ASUS: The error says to press F1 to enter the operating system (French page)
- ASUS: How to update the motherboard BIOS (French page)
Still seeing the message?
Reply to this topic with:
- The brand and exact model of your motherboard.
- The model of the CPU cooler or liquid cooler, and the header it is plugged into.
- The fan speed shown in the BIOS (in RPM).
- The full message displayed at startup.
- What was changed in the PC just before the message appeared.