Cooling Fan Comes On With Ignition [5 Easy Solutions]

The most common reasons behind the cooling fan comes on with ignition are a faulty temperature switch, damaged fan relay, faulty fan clutch, broken wire, and damaged ECU.

Keep reading this article to know more about these problems and find out the solution to each of these common problems. Let’s begin!

Cooling Fan Comes On With Ignition [5 Easy Solutions]

Cooling fans are essential to keep the engine at the optimum temperature. Any problem with the cooling fan shouldn’t be overlooked. We’ll look at the most common reasons car cooling fan keeps coming on in this section.

1. Faulty Temperature Switch

Before you try changing a bunch of parts or your fan, the first thing you should do is diagnose and replace the coolant temperature switch of your car. This is almost always the main reason that causes the cooling fan to come on when you start your engine.

The cooling fan is designed to come on when the engine reaches a temperature of more than 200 degrees. But if the temperature switch is faulty, it could cause the fan to come on whenever the engine starts.

That’s because the temperature switch is responsible to trigger the cooling fan to come on once the engine starts to become overheated. If it sends the signal even when the engine is hot, the cooling fan is designed to come on.


The temperature switch has to be replaced if it’s the culprit that’s causing the cooling fan comes on when the car is cold issue. It’s an easy job when you can locate the sensor. You have to take out the old one and replace it with a new one. The temperature sensor is inexpensive and easy to replace.

It’s easier to locate the temperature switch in older vehicles. But modern vehicles use Electronic Car modules (EDM) and Power Control modules (PCM). It’s a little more difficult to access the temperature switch in these modern cars.

Once you locate the temperature switch, it’s time to replace it. A lot of people recommend draining the coolant to avoid leaking. But if you can do the replacement quickly, you don’t have to drain the coolant as the leakage will be very small and it won’t bother your engine.

As a precaution, place a plastic bag under the temperature sensor so that the coolant falls on it and doesn’t stay in your vehicle. You’d need a socket wrench to unscrew the sensor. Spray it with some DW40 if you’re having difficulty unscrewing it.

Make sure that the new temperature sensor you’re installing has a thread lock and washer on it. If it doesn’t have these things, it might leak the coolant liquid.

2. Damaged Fan Relay

The fan relay is responsible for controlling the power supply of the fan. If you’re wondering why is my cooling fan always running, a damaged fan relay could very well be the reason behind it.


Before replacing a damaged fan relay, it’s important to diagnose and confirm if the fan is actually damaged. The process to do this fan relay troubleshooting is quick and easy.

Pull off the fan relay and place it in place of another relay. The other relay you choose should be one that you know is working properly and it’s non-critical to the function of the engine. Match the part numbers before you switch the relays. Both relays should have the same part number.

If the other part still works, that means the relay is okay. If it doesn’t work, you need to replace the fan relay. Fan relays are easily available and you can change them on your own.

3. Faulty Fan Clutch

In some of the older vehicles that don’t have an electrical system, the fan clutch could be the issue that keeps the fan constantly running. The motor of the fan is attached to the clutch such that the clutch can use the fan when needed.

But if the clutch has gone bad, it can start the fan at any time whenever you start the engine. If the fan starts and stops intermittently, the fan clutch can also be the reason behind this problem.


The clutch has to be replaced when it is damaged. Otherwise, you’d have no control over the fan. It takes expertise to access the clutch. You need to take off the engine cover and unscrew the manifolds to access the fan shroud. It’s a good idea to call in a technician if you don’t feel comfortable taking this on yourself.

4. Broken Wire

It doesn’t happen always but your fan could come on when you start the car due to broken wiring issues. You should check the wiring of your car if you’re sure that the temperature switch and the fan relays are okay.


You can replace the wiring harness of the fan if you see any broken wire. It’s up to you if you want to do it yourself or hire a mechanic to do it.

5. Damaged ECU

If the radiator fan turns on when the key is turned on, the problem could be with the ECU. If the temperature switch, fan relays, and wiring are okay, there’s a chance that the problem is the ECU.


It’s expensive to replace a damaged ECU. So, get your ECU diagnosed by a mechanic before you do anything drastic. In some cases, you can salvage the ECU and get it repaired at a much cheaper cost than having it replaced.

Why Cooling Fan Stays On When Engine Is Turned Off?

The cooling fan can come on in an overheating engine even if it’s not on. Cooling fans are designed to keep the engine at an operating temperature where the components and the engine are safe.

Some vehicles are designed to keep the cooling fan on even after the engine is shut off to get the engine back to the operating temperature. If the cooling fan in your vehicle stays on after turning off the engine, this is the most likely reason behind it.

There’s nothing to worry about if this is happening to you. All you have to do is wait for the engine to cool down. The fan will automatically turn off when the engine reaches the desired temperature.

Now that you know that fans can come on in a warm engine at any given time, always work with caution on a running engine. Keep your hands away from the fan blades when you’re working on an active engine to protect yourself from an injury.


When should the cooling fan come on?

The cooling fan should come on when the engine gets too hot. The fan assists the engine to operate at an acceptable temperature. If your fan comes on earlier than that, there’s something wrong.

What is the problem if the cooling fan keeps coming on?

If the cooling fan stays on or keeps coming on, it can drain the battery. The fan motor and blades can also get damaged due to overuse. The fan’s lifespan will be shortened if it keeps coming on.

Should the radiator fan come on when the car starts?

No, your radiator fan should start only when the engine gets hot and starts to go beyond the operating temperature.

Is it normal if the car fan keeps turning on and off?

Yes, the car fan is responsible to keep the engine at the right temperature. The fan will turn off when the engine reaches the desired temperature and it’ll turn on again once the engine gets overheated.

Can low coolant cause the fan to stay on?

Yes, the engine will be overheated if the level of coolant is too low. The fan will turn on and stay on much longer than it usually would to keep the engine temperature to normal.


Temperature control is an important part of a healthy engine. If it’s too hot, the components can be damaged. If it’s too cold, the engine becomes inefficient. That’s why the function of the cooling fan is essential to protect the engine.

Now you know the typical reasons behind a cooling fan coming on with the ignition and what you can do to solve this problem. We hope the tips we shared will help you get your engine back to the optimum temperature. Drop a comment if you have any questions about cooling fans.

Note: You can also read how to fix the blower motor speeds up and slows down the problem.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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