Why is my cooling fan not kicking in?

When a cooling fan won’t turn on, it’s usually a power or control issue: the fan itself may be dead, its cable loose or blocked, or the system’s temperature/BIOS settings are preventing spin-up.

Cooling fans appear in desktops, laptops, and servers to keep CPUs, GPUs, and chipsets from overheating. If one fails to spin, you may see rising temperatures, throttling, or system instability. This guide explains common causes and how to diagnose and fix the issue, with practical steps you can try safely.

What usually goes wrong

Common causes fall into hardware failures, connection problems, firmware/software controls, and airflow issues. Review the items below to identify what could be stopping your fan.

• Dead or failing fan bearing or motor



• Dust, lint, or debris obstructing the fan blades or heatsink


• Incorrect or mismatched fan control (PWM vs DC) or misconfigured BIOS/UEFI fan curve


• BIOS/UEFI or software settings that disable or delay spin-up at current temperatures


• Faulty temperature sensors or monitoring software giving erroneous readings


• Insufficient power supply or a failing motherboard header to drive the fan


• Damaged or faulty motherboard fan controller or header


• In laptops, blocked vents, degraded thermal paste, or a clogged cooling module

After checking these potential causes, you can proceed to targeted tests to confirm the root problem.

Troubleshooting steps

Use these step-by-step checks to diagnose and fix the issue, starting with safe, noninvasive actions and moving toward more involved tasks.

1. Power down, unplug, and ground yourself. If you’re on a laptop, disconnect the power adapter and remove the battery if possible.


2. Inspect physical connections. Look for loose or unplugged fan cables at the motherboard or power supply connectors. Re-seat any connectors securely.


3. Clean the fan and heatsink. Use canister compressed air to blow dust out of vents and blades. Hold the fan blades steady while you blow to prevent damage.


4. Test the fan on a known-good header or with a different fan. If you have a spare 3/4-pin connector or a different fan, swap connections to determine whether the issue is the fan or the header.


5. Enter BIOS/UEFI and check fan controls. Reset to defaults or set to automatic/Smart Fan. Save and reboot, then observe whether the fan spins up with increased temps.


6. Monitor temperatures and fan behavior with software. Use a hardware monitor utility (e.g., HWiNFO, HWMonitor) to see temps and fan speeds as the system loads. If temps rise and the fan still doesn’t spin, the control path may be faulty.


7. Update firmware and drivers. Update your motherboard BIOS/UEFI and any system management or chipset drivers from the manufacturer’s site. Some issues are caused by older firmware that misreads sensors or miscontrols fans.


8. Test power supply and motherboard health. If other devices on the same supply are unstable or you notice inconsistent voltages, you may have a power issue or a failing motherboard.


9. For laptops, reset the embedded controller (EC/SMC). Vendors provide specific procedures; consult your model’s manual. A reset can restore proper fan control in many cases.


10. Decide on next steps. If the fan works on another header or with another fan, replace the faulty component. If nothing works, professional diagnostics may be required.

If the fan still refuses to spin after these steps, a professional diagnosis may be needed to check for motherboard or power supply issues, or to replace the faulty fan or controller.

When to seek professional help

If you’re uncomfortable opening your PC, laptop or server, or if the issue persists after following the troubleshooting steps, contact a qualified technician. They can perform hardware checks, test power rails, verify sensor readings, and safely replace faulty components without risking damage to your system. For laptops, a service center can also heat-paste the CPU/GPU if thermal performance has degraded over time.

Prevention and best practices

Preventing fan and cooling problems involves routine maintenance and sensible usage habits. Consider the following:

• Regularly clean dust filters, vents, and fans to maintain unobstructed airflow


• Keep the computer environment cool and well-ventilated; avoid placing devices on soft surfaces that block vents


• Use quality fans with appropriate airflow (CFM) and keep a spare on hand for quick replacements


• Monitor temperatures and set sensible fan curves in BIOS/UEFI; avoid overly aggressive, noisy profiles unless needed


• Update BIOS/firmware from official sources and avoid unofficial tweaks that may destabilize fan control


• Replace thermal paste on aging desktops when temperatures rise or CPUs/GPU have degraded cooling

Desktop-specific tips

For desktops, pay attention to case airflow. Ensure intake and exhaust fans are balanced, cables are tidied to improve airflow, and dust buildup in power supplies or radiators is minimized.

Laptop-specific tips

Laptop care focuses on avoiding blocked vents, using the device on hard surfaces, and performing routine EC/SMC resets when recommended by the manufacturer. Consider using a cooling pad to improve airflow during heavy workloads.

Summary

A non-kicking cooling fan is usually caused by a combination of hardware faults, loose connections, firmware settings, or airflow problems. Start with a careful physical inspection and cleaning, verify power and headers, adjust BIOS/firmware controls, and test with known-good components. If problems persist, seek professional help to avoid damaged hardware and ensure reliable cooling for your system.

How do I know if my fan relay is blown?

Symptoms of a bad fan relay include engine overheating, a cooling fan that doesn't turn on, runs constantly, or cycles on and off inconsistently. You might also notice a non-functional air conditioner, blown fuses, the check engine light, or clicking and buzzing sounds from the control panel. 
Common symptoms

• Engine overheating: If the fan doesn't turn on when the engine is hot, especially at low speeds or while idling, it can cause the engine temperature to rise. 
• Inconsistent or non-functional fan: The fan may not turn on at all, or it might operate erratically, turning on and off at random times. 
• Fan runs constantly: A relay stuck in the "on" position will cause the fan to run continuously, even after the engine is shut off. 
• Poor A/C performance: A non-functioning fan can prevent the air conditioning system from cooling properly, particularly at low speeds. 
• Blown fuses or melted relays: A short in the relay can cause the fuse to blow, and a continuously running fan can cause the relay terminals to melt or burn due to excessive heat. 
• Check Engine Light: In many modern vehicles, a malfunctioning cooling fan relay can trigger the "Check Engine" or "Malfunction Indicator" light. 
• Unusual noises: You may hear clicking or buzzing from the control panel or relay, or the fan itself may make unusual sounds. 

What to do if you suspect a bad relay

• Safety first: Always turn off power to the system at the circuit breaker before inspecting any electrical components. 
• Visual inspection: Look for signs of damage, such as burning, melted plastic, or corrosion on the relay and wiring connections. 
• Test with a multimeter: Use a multimeter to test for continuity and proper voltage to the relay. 
• Rule out other issues: Check the thermostat and other control components to ensure the problem isn't originating from them. 
• Professional diagnosis: If you are not comfortable working with electrical systems, have a professional technician diagnose the issue to avoid potential injury or further damage. 

How to fix cooler fan not working?

Here's what to check for and how to fix it.

1. Damaged Electrical Fuse: The unit may not be receiving power because of a broken fuse.
2. Circuit Breaker Inspection: If the fuse is intact, look for the circuit breaker.
3. Power Cord Damage: Another possible issue could be with the power cord.

What tells the radiator fan to turn on?

The radiator fan is turned on by a signal from the engine's computer (ECU) or a dedicated control module, which is triggered primarily by the coolant temperature sensor. When the engine coolant becomes too hot, the sensor sends a signal to the ECU, which then activates the fan to force air over the radiator and cool the fluid. On most vehicles, the fan will also automatically turn on when the air conditioning is activated.
 
This video explains how the radiator fan works and why it's important for cooling the engine: 1mOnline Mechanic TipsYouTube · Apr 18, 2025
Key triggers for turning the fan on:

• Coolant temperature: This is the primary reason. The coolant temperature sensor detects that the engine is getting too hot and sends a signal to the vehicle's computer to turn on the fan. 
• Air conditioning (AC) system: When you turn on the AC, the system's compressor engages, and this also triggers the radiator fan to turn on, even if the engine is cold. This is because the compressor creates an additional load and heat on the engine. 
• Heavy traffic: When the vehicle is stationary, there isn't enough airflow from driving to cool the radiator, so the fan turns on to compensate for the lack of air movement. 
• Fan control module: Some vehicles have a separate fan control module that receives input from the temperature sensor to manage the fan's operation, sometimes with multiple speeds. 
• Faulty sensor: A malfunctioning coolant temperature sensor can send incorrect readings to the ECU, which may cause the fan to turn on when it shouldn't or not at all. 

This video demonstrates how to test a radiator fan switch: 52sCarsNToysYouTube · Jan 25, 2021

How to check if a radiator fan is working?

You can check if a radiator fan is working by seeing if it turns on when the engine gets hot and the AC is on, or by directly testing the motor with jumper wires connected to a 12-volt battery. A failing fan may also indicate other issues like a bad fuse, relay, or temperature sensor, which can be tested as well. 
Method 1: Check with the engine running 
This video demonstrates how to check your radiator fan with the engine running: 52sArty's GarageYouTube · May 22, 2015

• Start the engine and let it idle, or drive the car until it reaches normal operating temperature. 
• Turn the air conditioner to its highest setting. 
• Observe the engine temperature gauge to ensure it doesn't get too hot. 
• Listen for the radiator fan to turn on. It should activate when the engine is hot, even with the AC off, to help cool the engine. 
• If the fan turns on, it's likely working correctly. If it still doesn't, the problem is likely not the fan itself, but another component in the cooling system. 

Method 2: Test the motor directly 
You can watch this video to see how to directly test the fan motor with jumper wires: 58sCarsNToysYouTube · Sep 23, 2014

• Safety first: Make sure the engine is off and cool before you begin. Wear safety glasses and gloves. 
• Locate the fan's electrical connector, unplug it, and identify the two terminals. 
• Use jumper wires with alligator clips to connect the fan's terminals directly to a 12-volt power source, like the car battery. Connect the positive and negative wires to the corresponding terminals on the fan's harness. 
• The fan should spin at full speed. If it does, the motor is working and the issue is likely with the fan's control system, such as a fuse, relay, or sensor. 
• If the fan does not spin, the motor is likely bad and needs to be replaced. 

Method 3: Check fuses and relays 
This video explains how to check your radiator fan relay: 56sCB7 MediaYouTube · Jul 10, 2022

• Locate your vehicle's fuse box, usually under the hood. 
• Find the fuse and relay specifically for the cooling fan. 
• Visually inspect the fuse to see if it's blown. If it is, replace it. 
• If the fuse looks okay, try swapping the fan relay with an identical one from a non-critical circuit (like the power windows) to see if the fan starts working. 
• If the fan works after the swap, the original relay was bad and needs to be replaced. 

What to do if the fan isn't working

• If the fan motor is working but it's not turning on when needed, check the fuses, relays, and wiring for any damage. 
• If the fan is functional, the problem could be a faulty thermostat, temperature sensor, or water pump. 
• If you've tested the fan directly and it doesn't spin, it is the source of the problem and needs to be replaced.