Electric Cooling Fan Problems

Updated on March 12, 2017
Testing a failed cooling fan circuit can be tricky at times.
Testing a failed cooling fan circuit can be tricky at times. | Source

Cooling fan problems can be hard to diagnose--and confusing--depending on your vehicle model and the type of failure. Still, you can avoid much of the confusion using a troubleshooting plan.

If your electric radiator fan isn't coming on after the engine reaches operating temperature--the key here is operating temperature (more on this later)--you can bet there's something wrong with the fan assembly itself, the circuit, or one of its components.

This guide walks you through some of the most common electric cooling fan problems to help you troubleshoot and identify the problem when the fan refuses to work, or works intermittently.

On older vehicle models, the fan circuit is simple, and you may not have trouble locating operating components or the fault itself.

Modern vehicles use the electronic control module (ECM-car computer), powertrain control module (PCM), or a dedicated fan control module (or both) to control the operation of the radiator fan, and can be little more complicated to troubleshoot sometimes.

So, with newer vehicle models, it's a good idea to have the vehicle repair manual for your particular make and model on hand, specially with fairly recent models. The manual explains the operation of the cooling system, how your cooling fan operates, and the sensors or switches your car computer reads from to operate the cooling fan. Besides, the manual can help you locate sensors, relays, switches and trace circuit wires as necessary.

If your engine is overheating and you suspect problems with the cooling fan, this guide gives you important troubleshooting tips, and the steps to diagnose the most common cooling fan failures you are likely to encounter on your car.

Before going into the necessary steps to troubleshoot the fan in your vehicle, though, a brief fan operation description follows.

I. Cooling Fan Operation
Troubleshooting Shortcuts
II. Cooling Fan Troubleshooting
A. Has Your Cooling Fan Actually Failed?
B. How to Test the Cooling Fan Motor
C. Checking Wires, Connectors and Related Components
D. Testing the Cooling Fan Temperature Switch
E. Testing a Cooling Fan Relay
Cooling fan helps control engine and other components temperature in the engine compartment.
Cooling fan helps control engine and other components temperature in the engine compartment. | Source

I. Cooling Fan Operation

If the cooling system in your vehicle uses an electric cooling fan, most likely you have a transversal (sideways) mounted engine. However, some longitudinal (front to rear) mounted engines use the electric fan as well, but they usually have an engine-powered cooling fan.

The electric cooling fan uses a direct current (DC) electric motor with a thermo switch, module or computer control to turn it on or off, depending on coolant temperature or AC operating condition.

On older fan circuits, the thermostatic switch connects to battery power on one side, and to the fan motor on the other. However, on most 90s and newer models the control was passed to the car computer or a dedicated module. For example, when coolant temperature changes, the thermo switch reports this change to the computer through a voltage signal, which the computer or module uses to activate the cooling fan through a fan relay(s).

An electric cooling fan not only helps save energy by running only when the system needs to remove excess heat away from the engine, but helps shield other sensitive circuits and electronic components from heat damage. During the winter months, your radiator fan saves even more energy when enough cool air flows through the radiator on the highway.

Even if your cooling fan doesn't have a complicated circuit, you still need to know where to look when your fan doesn't work as expected. Next are some fan circuit key points you need to check when diagnosing problems with your electric cooling fan.

A bad temperature gauge can mislead you.
A bad temperature gauge can mislead you. | Source

Troubleshooting Shortcuts

1. If you think the cooling fan isn't working because your temperature gauge is indicating overheating, open the hood, start the engine and let it idle for 15 to 20 minutes. If the fan comes on, you may have a bad temperature sensor or gauge.

2. A cooling fan temperature switch (or sensor in some vehicles) can also get stuck, which may cause the fan to run continuously any time your turn the ignition key on or start the engine. Troubleshoot the switch.

3. On some modern vehicles, an ambient air temperature sensor, vehicle speed sensor, and other sensors may provide input to the car computer to determine radiator fan operation. Consult your vehicle repair manual to check the required sensors and switches.


On a warm engine, the fan may come on even if the engine is not running. When working on a hot engine or testing running components in your engine, keep your hands and tools away from the fan blades and moving components when making diagnostics that require the engine to be running.

Locate cooling fan circuit components.
Locate cooling fan circuit components. | Source

II. Cooling Fan Troubleshooting

Troubleshooting a cooling fan that doesn't work can be a relatively straightforward task at times. Usually, the problem resides with the fan motor itself, a thermo switch, relay, wire, or (although not as common) the computer or module itself.

A. Has Your Cooling Fan Actually Failed?

On many modern vehicles, if you want to confirm whether your cooling fan is in working order, you can start the engine and let it idle. Set your air conditioning to the MAX setting and turn it on. The cooling fan should come on immediately or within the next couple of minutes. On older vehicle models, just wait about 15 to 20 minutes for the engine to reach operating temperature. Then, the fan should come on.

* If the fan comes on when the AC is running at MAX, but doesn't run when the engine is hot, check the temperature sensor or switch that sends the signal to the computer or module to operate the fan. On modern vehicles, a bad sensor usually triggers the check engine light. Scan the computer for trouble codes, if necessary.

* If the fan fails to come on, first check for a fan blown fuse or triggered breaker. On older vehicle models, you may have a fusible link in the circuit. This is a piece of wire inside an insulated piece of marked block of rubber. You won't miss it. Grab the ends of the fusible link and try to stretch it. If it does, the wire link might be broken. Replace it.

CAUTION: If the fan fuse or fusible link is blown, or the breaker has been triggered, it is possible the fan motor itself may be bad and causing the fuses to blow. Replace the fuse, fusible link or reset the breaker and test the fan motor again. If the same problem appears and there's no wire causing a short circuit, replace the fan motor.

NOTE: if the cooling fan doesn't come on when the engine has been operating for 20 minutes or more, make sure that coolant is reaching operating temperature, around 220F (104C). You may be dealing with a stuck-open thermostat. Check the temperature of the engine block and radiator tank (the one that connects to the engine with the upper radiator hose) using a kitchen thermometer. Make sure that engine temperature reaches about 220F(104C) and the radiator tank temperature rises accordingly (meaning hot coolant is being transferred to the radiator). If temperature remains fairly steady around 200F (93C) or less, the temperature switch or sensor may fail to trigger the radiator fan on.

Connect fan directly to power for testing.
Connect fan directly to power for testing. | Source

B. How to Test the Cooling Fan Motor

If the fan fails to come on, you still can check the fan by connecting direct battery power to it (while working and making tests in the proximity of the fan, always stay clear and keep tools away from the fan).

1. Unplug the fan wiring connector. Closely examine the connector for corrosion or damage. If necessary, use electrical contact cleaner to clean the connector. Make sure the wires are firmly attached to the connector and not damaged.

2. Look at the polarity of the wires leading to the fan, identify power and ground (usually a black wire).

3. Using jumping wires, connect battery negative to the ground side of the fan connector and positive battery to the other wire. On some vehicles, the fan connector comes with three terminals, two for power (high and low speed, test both) and another for ground. Or a four wire terminal (high and low speed and two grounds, test each pair separately).

Consult your vehicle repair manual to identify each wire, if necessary.

4. Once you connect the fan to battery power, your fan should start running.

* If the fan doesn't work with direct battery power, examine the terminal that plugs to the radiator fan connector. Look for corrosion and damage. Then test for incoming voltage at the terminal with your digital multimeter (DMM). With the engine running and at operating temperature, touch the terminal positive and ground with the respective multimeter probes, you should get running voltage (about 14V), indicating the fan should be running. If your test proves incoming power, replace the fan motor.

* Check for any blown fuses or a tripping breaker. If your find a circuit blown fuse or tripped breaker, the fan motor might be pulling too much voltage, causing the fault. Check for a shorted wire or replace the fan motor.

* If the fan doesn't come on at all, or runs noisy or at an abnormal low speed, replace the fan motor.

Still, on some vehicle models, you can unplug the single wire connector from the coolant temperature switch to trigger the cooling fan on, or by grounding the wire using a jumper wire while the vehicle is running. Just keep in mind that your computer may set a trouble code for a malfunctioning temperature switch

The video at the bottom of this post gives you a visual guide to troubleshoot the temperature sensor and fan motor.

C. Checking Wires, Connectors and Related Components

When the cooling fan motor and fuses, breakers or fusible links seem to be in working order, it's time to check the circuit and related components. You may need to consult your vehicle repair manual to locate components and wires in the circuit.

Try to follow the fan wires back to the coolant temperature switch or cooling fan relay on modern vehicles. Closely examine the wires for cuts or damage.

Sensor(s) in the cooling fan circuit handles the signal to turn on the cooling fan.
Sensor(s) in the cooling fan circuit handles the signal to turn on the cooling fan. | Source

D. Testing the Cooling Fan Temperature Switch

Consult your vehicle repair manual to locate the switch, if necessary. On most modern vehicles (late 90s and newer), you are looking for the switch that connects to your car computer (powertrain computer), since there may be more than one switch.

You can test the cooling fan temperature switch using a test light.

1. Connect your test light to battery ground.

2. Start and idle the engine, and backprobe the connector terminals with the test light. One of them should turn on the test light.

3. Wait for the engine to reach operating temperature.

4. Now backprobe the other wire at the connector. Your test light should come on. Otherwise, the switch is not working.

NOTE: If your vehicle repair manual gives you the cold and hot Ohms (resistance) values for your temperature switch, you can test it with a digital multimeter. Test switch resistance with the engine cold, and after idling the engine for 15 minutes. Turn off the engine and test again. Compare values to the ones on your manual. If you don't have the cold and hot values for your switch, you still may want to test the switch and compare the difference in values. This will tell you the switch is still working somehow.

Also, on newer vehicles the coolant temperature sensor to operate the A/C and the cooling fan. If your vehicle repair manual gives the Ohms values at cold and hot condition, use your voltmeter to test the temperature sensor, if necessary. If you don't have the sensor's resistance values but you notice that Ohms remains pretty much the same at cold and hot, replace the sensor.

Test the fan relay for operation.
Test the fan relay for operation. | Source

E. Testing a Cooling Fan Relay

* The easiest way to know whether your relay is causing trouble is to replace it with another relay in your vehicle you know it's working fine. Look at the power center under the hood for a similar relay that won't interfere with the correct operation of your engine if swapped, like a window or wiper relay.

* If you can't find a suitable relay, you still can test the relay. Go ahead and read the steps described in How to Test a Fuel Pump Relay. The steps are the same for your relay. Most fan relays come in one of three different configurations. Make sure to correctly identify the prong terminals on your relay. See the schematic printed on the relay itself or consult your the schematic on your vehicle repair manual, if necessary. The schematic will help you also when checking the fan cooling circuit.

* If swapping relays still doesn't operate your cooling fan, make sure the relay is receiving power from the computer.

* Consult your repair manual to identify the wire that sends power to the relay. Usually, there's power to the relay even if the engine is off. You can use a test light to check for power here. Connect the test light wire to a good ground and probe the power terminal on the relay socket. Turn the ignition key to On, if necessary. The test light should come on. If there's no power, there may be a fusible connector hooked to the power wire that is at fault, or the computer is not sending power to the relay. Consult the circuit schematic on your repair manual to follow the wire back and keep checking for voltage as necessary.

* If the relay is working, check the wire(s) and fan connector for damage.

When checking for cooling fan problems, a modern vehicle may present a challenge. Many modern vehicle models have a much more complex cooling fan circuit that the ones described here. Refer to your vehicle repair manual to locate wires, components, and modules, if necessary. Still, in some cases, you need to make a diagnosis using a professional scan tool to check for voltage values and power inputs to the cooling fan to locate the source of the problem.

Questions & Answers

  • My cooling fan is not working on overheating, but it works with A/C. Why is this?

    You may want to check the coolant temperature sensor.

  • Why does my 2012 Silverado volt gauge drop from 14+v to about 12v when the electric fan is running?

    Electric fans draw quite a bit of amperage and it's possible for some alternators to lack a sense of such high draw if it is not designed for it. Still the alternator should be putting out over 13 volts, even if your meter says otherwise. Check the alternator and battery with a Voltmeter. Regardless of the type of charging system, there's always a drop in voltage. So most likely there's no problem with your alternator.

  • my cooling fans start immediately when I plug the battery on switch off stats again until the battery is dead. What could be faulty?

    There seems to be a short in the circuit. You may need the diagram for your model to check for voltages.

  • My 2006 G35 is not overheating, but when the car gets up to operating temperature, both fans come on high and do not turn off until I shut the car off. What should I look into to remedy this?

    Check the coolant fan relay and coolant temperature sensor.

  • I have a 2008 Mercedes GL 450. The cooling fan doesn't run even at a high temperature. Turned on the Airconditioner but still doesn't run. What is the problem?

    Check the fan switch (coolant temp sensor) and the circuit. You may need the vehicle repair manual for your model to I.D. the wires.


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    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      2 months ago

      Check for power to the relay with the ignition On first. Other possibilities is a defective or disconnected module. If there's no problem with the AC, you may use the diagram to trace for voltage. You can find the diagram in the repair manual for your vehicle. Use an aftermarket manual, if necessary.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      2 months ago

      Check the temperature sensor. If the sensor is fine, check the wires. Make sure they are well connected, not loose.

    • profile image


      2 months ago

      I have a 2006 Dodge caravan, I had the radiator replaced about 6 months ago my recent problem is the fan comes on when it's not even warmed up, once it comes on it seems to stay on until I turn my van off.

    • profile image


      2 months ago

      My Hyjndai Azera 2009 fan wont start, fan tested okay, relay tested okay, module tested okay. There seems to be no power to the relay and module. Been battling for 3days now

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      2 months ago

      Hi RR,

      It's possible. If you think the fan is running when it shouldn't check for possible DTCs, even if your engine light is not on. You may need your repair manual to check on some sensors.

    • profile image

      Rick Brooks 

      2 months ago

      On 2009 GMC with 5.3 L . Can the ambient temperature sensor cause electric radiator fan to run even when engine is overnight cold when AC is on for several minutes as I drive ?

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      3 months ago

      Hi RH

      Follow the voltage using a diagram. Both fans should come on at the same time - they're wired in parallel. Check where the voltage is stuck for that side.

      Sorry can't be of any more help.

    • profile image

      R Harris 

      3 months ago

      I have a 2006 Pontiac Grand Prix 3.8 Supercharged. I have replaced: Coolant temperature sensor, thermostat, PCM, Both fans (complete unit), Wiring from the fans to the relays and plugs oh and the relays yet the driver side fan still wont come on. Fans have been tested both the old and new (and they worked), but I can't get this fixed. Any suggestions?

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      3 months ago

      Yes. If the engine starts to overheat, you can end up with an expensive repair. So it's better to take a look at it now that can be much cheaper.

    • profile image

      shannon dillon 

      3 months ago

      it is a good idea to get someone to check it out if you have a problem with the fan cooling system

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      3 months ago

      It's possible there's a failing pressure switch in the AC. If you have a capable scanner, the circuit may be monitor to check the switches.

    • profile image


      3 months ago

      Hi, I have Mitsubishi gallant v6 2004. My cooling fans does come on and with AC on they do increases speed but not to the max speed even when the engine is overheating. They stay on same speed without AC even if the needle is going above the middle. Only increases speed with AC on, but not very fast just little difference. If I unplugged the ECU wire from the module main connector they run full speed all the time and no heating issue.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      6 months ago

      Hi RW,

      Sorry, I don't have the wiring diagram for this model but look for the fuse box, either under the dashboard or in the engine bay, ---firewall, driver's side possibly.

      Hope this helps

    • profile image

      Ray Waldin-Walker 

      6 months ago

      I have a 1992 Volkswagen Hatchback 1Lt petrol, "the old bread van", boils when reaches over temp, ok when air cools eng on a run till i stop. fan motor ok, checked with 12v source separate, changed rad sensor, no go where is rad motor relay?

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      8 months ago

      Hi Prasit,

      You need the wiring diagram for the cooling fan of your particular vehicle make and model. Recheck the connections you made and the fuses. It seems that somewhere you created a short. If you replaced the cooling fan, make sure it's the right one for your model. If you don't have the manual for your car, check the reference section of your local public library.

      Good luck

    • profile image


      8 months ago

      My Toyota Soluna 1997 5A-FE 2 ECM's Resistor, Diode and transistor burnt out , after replaced plug into Car Cooling Fan running immediately and Magnetic Clutch of AIR Cond not be operated then ECM burnt in same position excluded Diode (Engine can be start and running)

      Would you please diagnoses the major shorts.

      Thank you

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      8 months ago

      Hi Mike,

      Basically the black wire is ground and the blue one is positive. I don't have the wiring diagram for your model, but I'm assuming you are connecting to the control module. Check the fuse and make sure there's power. If you don't have the service manual for your particular model, stop by your local public library. The reference section might have the manual for your model.

      Good luck.

    • MikeN70 profile image


      8 months ago

      I recently purchased a new Universal 120w cooling fan for my BMW 318iS. The wires from the car are brown, blue, another colour with a stripe in. The universal fan has only 2 wires, one black & one blue. Which wires need to be connected to allow the fan come on when the car gets hot.

      Presently the striped wire is not connected & after driving about 12 kilometers the temp gauge started to rise & the fan did not come on.

      Please help!

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      8 months ago

      Hi murlly

      It's possibly there's a short circuit or a problem in the cooling system. Try scanning for trouble codes, if necessary.

      Good luck

    • profile image


      8 months ago

      Tkz for good information ...my car problem model chevrolet nabira 1.8 sport cooling fan sometimes non stop run 30 minit sumting and aircond automaticly cut off.. after 30 minit normal running cooling function

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      13 months ago

      Glad it helped.

      Thanks for the comment.

      Good luck

    • profile image

      Adam O. 

      13 months ago

      Man, this helped out a lot!! Well written / explained! Thank u.


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