When you power on your PC you get a black screen with the message “CPU Fan Error! Press F1 to Resume” or “CPU FAN Error” and the system refuses to boot into Windows until you press a key. The fans may be spinning loudly, slowly, or not at all, and the error returns every cold boot even after you press F1. On some ASUS, MSI, and Gigabyte boards the system will immediately shut down after a few seconds to protect the processor.
This is a protection mechanism, not a random glitch. Your motherboard cannot detect a reliable RPM signal from the CPU cooler, so it assumes the CPU is uncooled and halts startup to prevent thermal damage. You should not ignore or permanently bypass it without fixing the root cause, but it is usually fixable in under 30 minutes without new parts. As of 2026, most modern UEFI BIOS versions still enforce the same CPU fan detection logic as older boards, so the steps below apply to both legacy BIOS and current UEFI systems.
Likely Causes
| Cause | How to confirm | Fix difficulty |
|---|---|---|
| CPU fan plugged into wrong header (CHA_FAN, SYS_FAN, or AIO_PUMP instead of CPU_FAN) | Open case and trace cable from CPU cooler to motherboard header label printed on PCB | Easy |
| Loose or partially seated fan connector | Fan spins intermittently or RPM reads 0 or N/A in BIOS under Monitor or Hardware Monitor | Easy |
| BIOS fan speed warning threshold set too high | Fan spins at 400-600 RPM on boot but BIOS lower limit is 600 or 800 RPM | Easy |
| Dust buildup or obstructed fan blades | Fan struggles to start, makes grinding noise, or stops after a nudge | Easy |
| Outdated or corrupted BIOS failing to read PWM signal | Error started after hardware change, BIOS version is several releases behind on support page | Moderate |
| Failing fan motor or damaged RPM wire | Fan does not spin at all even when set to 100 percent in BIOS, or spins but reports 0 RPM | Moderate |
Fix 1: Reseat the CPU Fan Header Connection
What causes it
Vibration and case movement can work the 3-pin or 4-pin connector slightly out of the CPU_FAN header. Even one millimeter of lift can break the RPM sense pin connection while still delivering power, so the fan spins but the motherboard reads 0 RPM.
How to check
Shut down Windows via Start > Power > Shut down, switch the power supply off with the rear 0/1 switch, and unplug the power cable. Remove the side panel and locate the cable coming from the top of the CPU cooler. Follow it to the motherboard. The header should be labeled CPU_FAN and is usually located directly above or to the right of the CPU socket. If it is connected to CHA_FAN1, SYS_FAN1, CPU_OPT, or AIO_PUMP, that is the problem.
What to do
Pinch the fan connector by its plastic housing and pull straight up to disconnect it. Inspect the header pins for bending. Align the plastic guide tab on the connector with the notch on the header and press firmly until the connector sits flush with the header base with no gap. Route the cable so it does not pull taut when the side panel is closed. Plug the power cable back in, switch the PSU on, and boot. Enter BIOS to verify the fan is detected.
How to undo it
If the error persists, power off and return the connector to its previous header. No BIOS setting was changed, so no further undo is needed.
Fix 2: Verify the Fan Spins and Clear Dust Obstruction
What causes it
A thick layer of dust on the heatsink fins and fan hub increases startup friction. The fan may need a higher voltage to start than the BIOS supplies during the initial POST check, so it fails the RPM test even though it would spin a second later.
How to check
With the case open and power on, watch the CPU fan during the first 5 seconds after pressing the power button. If it twitches, rocks back and forth, or starts only after you give it a light tap with a finger, it is obstructed. Listen for a buzzing or clicking sound that indicates the bearing is struggling.
What to do
Power off, switch off the PSU, and unplug the cable. Use compressed air in short 2-second bursts to blow dust from the fan blades, heatsink fins, and the hub center. Hold the fan blades with one finger to prevent overspinning. For caked dust, use a soft brush or cotton swab. Do not use a vacuum directly on the motherboard. Reconnect power and boot.
How to undo it
This is a cleaning step with no settings to revert. If you removed the fan from the heatsink for cleaning, remount it in the same orientation with the airflow arrow pointing toward the rear exhaust.
Fix 3: Lower the CPU Fan Speed Low Limit in BIOS
What causes it
Many high-efficiency 120mm and 140mm coolers idle at 300 to 500 RPM. If the BIOS setting called CPU Fan Speed Low Limit or CPU FAN Fail Warning is set to 600 RPM or 800 RPM, the BIOS will trigger a CPU Fan Error even though the fan is healthy and cooling normally.
How to check
Enter BIOS by tapping Delete or F2 repeatedly during boot. On ASUS boards go to Monitor > Fan Speed Monitor > CPU Fan Speed. On MSI go to Hardware Monitor > CPU Fan. On Gigabyte go to Smart Fan 6 > CPU_FAN. Look for the current RPM reading and the field labeled CPU Fan Speed Low Limit, Fan Fail Warning, or Minimum Speed Warning. If current RPM is below the limit value, this is your cause.
What to do
In the same menu, change CPU Fan Speed Low Limit from 600 RPM or 800 RPM to 200 RPM or 300 RPM. If your BIOS offers an Ignore option, do not use it yet. Instead set it to the lowest numeric value. On ASUS you can also set CPU Fan Speed from N/A to a numeric value. Press F10 to Save and Exit, confirm Yes, and restart. The error should disappear if the fan now exceeds the lower threshold.
How to undo it
Re-enter BIOS with Delete or F2, return to Monitor > Fan Speed Monitor, and set CPU Fan Speed Low Limit back to 600 RPM or its original value. Press F10 to save.
Fix 4: Set Correct Fan Control Mode and Disable False Pump Detection
What causes it
A 3-pin DC fan running in PWM mode or a 4-pin PWM fan running in DC mode can report an incorrect RPM signal. All-in-one liquid coolers connected to CPU_FAN can also confuse detection if the board expects an air-cooler RPM curve.
How to check
In BIOS under Monitor > Q-Fan Configuration on ASUS, Fan Control on MSI, or Smart Fan 6 on Gigabyte, check the mode for CPU_FAN. It will show Auto, PWM, or DC. Check your fan cable: 4 wires means PWM, 3 wires means DC. Mismatched mode is common after a BIOS reset.
What to do
Set CPU Fan Control Mode to match your hardware. For a 4-pin fan choose PWM Mode. For a 3-pin fan choose DC Mode. Set CPU Q-Fan Control or Smart Fan Control to Enabled or Auto. If you use an AIO, the radiator fans should be on CPU_FAN and the pump on AIO_PUMP or PUMP_FAN1, not the reverse. For AIO setups, set AIO_PUMP header to Full Speed or Disabled monitoring. Press F10 to save and exit. Boot and confirm RPM is stable between 600 and 1500 RPM depending on temperature.
How to undo it
Return to the same Q-Fan or Smart Fan menu and set CPU Fan Control Mode back to Auto. For AIOs, set the pump header back to its previous control mode.
Fix 5: Update the Motherboard BIOS
What causes it
Early BIOS versions may misread low-RPM fans from newer coolers or have a bug in the Super I/O fan detection routine. This often appears after you install a new CPU cooler that was not available when the board shipped.
How to check
In BIOS, note the BIOS version on the Main or Information page, listed as BIOS Version or UEFI Version, for example 1402 or F10. In Windows, press Windows Key + R, type msinfo32, and press Enter to confirm BIOS Version/Date. Compare it to the latest version listed for your exact motherboard model on the manufacturer’s support site. If you are two or more revisions behind, an update is warranted.
What to do
Download the latest BIOS file to a FAT32 formatted USB drive. Rename it if the manufacturer requires it, such as CREATIVE.ROM for ASUS USB BIOS Flashback. Restart and enter BIOS. Use the built-in tool: EZ Flash 3 in Tool > ASUS EZ Flash 3 Utility, M-Flash on MSI, or Q-Flash in BIOS on Gigabyte. Select the file on the USB drive and start the update. Do not power off during the process. The system will reboot automatically when complete. Re-enter BIOS and recheck the fan RPM reading.
How to undo it
BIOS downgrade is rarely needed and can be blocked on some boards. If the new BIOS causes issues, use the same EZ Flash, M-Flash, or Q-Flash tool to flash the previous version file you saved on the USB drive. Load Optimized Defaults in Exit > Load Optimized Defaults after downgrading.
Fix 6: Test With a Different Fan Header or Replace the Fan
What causes it
The RPM sense wire inside the fan cable can break internally while the power wires remain intact. The fan spins normally but never sends a tachometer pulse, so every header reads 0 RPM and the motherboard always throws the error.
How to check
In BIOS Hardware Monitor, set CPU Fan to Full Speed or Manual > 100 percent. If the fan spins at full speed but the RPM field still shows N/A or 0 RPM, the tach wire or motor board has failed. To confirm the header is not dead, temporarily connect a case fan to the CPU_FAN header. If the case fan reports an RPM, the CPU cooler fan is faulty.
What to do
Power off and switch off the PSU. Unscrew the fan from the heatsink – usually four Phillips screws in the corners – and disconnect it. Install a replacement PWM fan of the same size, typically 92mm, 120mm, or 140mm, with a 4-pin connector. Secure it with the original screws with airflow pushing through the heatsink toward the rear exhaust. Plug the new fan into CPU_FAN. Boot and verify RPM reads 800 to 1800 RPM and the error is gone. If you need an immediate boot, you can connect the working case fan to CPU_FAN as a temporary test.
How to undo it
Power off, reinstall the original fan, and plug it back into CPU_FAN. If you moved a case fan, return it to its original CHA_FAN or SYS_FAN header so case airflow is restored.
Fix 7: Reset CMOS and Reconfigure Warning Settings
What causes it
A corrupted CMOS setting from a failed overclock, power loss, or dead CMOS battery can lock the CPU Fan Error state on even when hardware is fine. The BIOS may also be stuck with Halt On All Errors enabled.
How to check
If all previous fixes show a healthy RPM in BIOS but the error still appears on every cold boot and disappears on warm reboot, the CMOS settings are suspect. Also check if the system clock resets to a wrong date after being unplugged overnight, which indicates a weak CR2032 battery.
What to do
Power off, switch off PSU, and unplug. Press and hold the case power button for 10 seconds to drain residual power. Remove the silver CR2032 coin battery from the motherboard for 5 minutes, or short the CLRTC or JBAT1 pins with a screwdriver for 10 seconds as labeled near the battery. Reinstall the battery, plug in, and power on. Enter BIOS with Delete or F2. Go to Boot > Boot Configuration or Boot > Wait for F1 If Error and set Wait for F1 If Error to Disabled only after confirming the fan reports a valid RPM, and set CPU Fan Speed Low Limit to 200 RPM. Go to Exit > Save Changes and Reset. Set the correct date and time in BIOS or Windows Settings > Time and Language.
How to undo it
Re-enter BIOS and set Wait for F1 If Error back to Enabled so future fan failures will halt the system safely. If you disabled Halt On Error, re-enable it. No hardware removal needs to be undone beyond reinserting the battery.
If Nothing Works
If the error remains even though a known good fan reports RPM on CPU_FAN, the header’s sense pin may be physically damaged. Inspect the CPU_FAN header with a flashlight for bent pins or blackening. Try booting with the CPU cooler fan connected to CPU_OPT or CHA_FAN1 and then in BIOS set Monitor > CPU Fan Speed to Ignore and set Chassis Fan 1 Speed Low Limit to 200 RPM so that header provides monitoring. This lets you boot safely while you plan a repair.
For motherboards that still refuse to POST, check for a failing pump if you use an AIO. A dead pump will read 0 RPM on AIO_PUMP and trigger the same halt. Replace the CMOS CR2032 battery with a new one, rated 3 volts, if voltage is below 2.8 volts. If the board is under warranty, document the BIOS version, fan model, and RPM readings with photos and contact the board manufacturer for RMA, as a damaged Super I/O controller requires board-level service.
FAQ
Can I just set CPU Fan Speed to Ignore to bypass the error
You can in BIOS under Monitor > CPU Fan Speed > Ignore, which lets the system boot without CPU fan detection. Only do this as a temporary test after you have visually confirmed the fan or pump is actually spinning and CPU temperatures are normal. Running long term on Ignore hides a real cooling failure. Under Settings > Monitoring, keep temperature warnings enabled and check core temperature with HWMonitor or HWiNFO to ensure idle stays below 45 degrees Celsius and load below 85 degrees Celsius.
Why does the error only appear on cold boot and not on restart
On a cold boot the BIOS checks RPM within 1 to 2 seconds of power on. A dusty or low-speed fan may not reach the 600 RPM threshold in that window but will after 5 seconds. On a warm restart the fan is already spinning and passes the test. Lowering the low limit to 200 RPM as described in Fix 3 usually resolves this without hiding the warning.
I have an AIO liquid cooler, which header should I use
Connect the pump’s 3-pin or 4-pin cable to AIO_PUMP or PUMP_FAN1, and connect the radiator fans to CPU_FAN. In BIOS set AIO_PUMP to Full Speed or 100 percent duty, and set CPU_FAN to PWM or Auto depending on the radiator fans. If your board has no dedicated pump header, connect the pump to CPU_FAN and the radiator fans to CPU_OPT, then set CPU_FAN to Full Speed so the pump never slows. The error appears when the pump is on the wrong header and the BIOS sees 0 RPM on CPU_FAN.
What RPM should my CPU fan show in BIOS
Expect 600 to 1000 RPM at idle for most 120mm air coolers and 800 to 1800 RPM under load when set to Standard or Balanced curve. In BIOS under Q-Fan Configuration or Smart Fan 6 you can set the curve with points such as 40 degrees Celsius at 30 percent, 65 degrees Celsius at 60 percent, and 75 degrees Celsius at 100 percent. If RPM is consistently below 300 RPM or shows N/A, reseat the header or replace the fan.
