Cooling fan comes on when the car is cold? Here’s why

The cooling fan of a car can sometimes act unbelievably regardless of whether it’s sound or faulty. For example, it may come on even when the engine is at normal operating temperatures where extra cooling isn’t necessary.

So, why does the cooling fan runs even when the car is cold?

A lot of issues(some minor, others major), can cause this problem. These include your climate control system. If it’s activated, your fan could misbehave a little bit. A failing coolant temperature sensor, not to mention, electronic engine control unit (ECU) problems could also be culprits.

What Are the Causes Of An Active Cooling Fan When the Car Is Cold?

Your Climate Control System

The climate control system is a special feature in modern cars that enables you to manage the cabin temperature of your vehicle with precision. It’s made up of multiple, smaller systems that work together to achieve this purpose.

Now, your fan relies on a control unit to turn on and off as need be. The unit sits above the radiator. It takes signals from two temp sender units(located on the engine and in the bottom radiator hose, respectively), thereby activating the fan when need be.

But, there is a temperature sender unit on the aircon system. Sometimes, this can also trigger your fan whenever the climate control is on, regardless of the engine’s temperature.

A Faulty Coolant Temperature Sensor

Did you know that your car(if modern) has between 15-30 sensors to keep the vehicle running seamlessly? Of these, one of the most important sensors is the coolant temperature sensor.

This temperature sensor monitors and sends engine temperature information to the ECU. The computer then decides whether to turn the fan on or off, depending on how hot or cold the engine is.

Now, a faulty coolant temperature sensor may not be able to monitor the engine’s temperature correctly. Consequently, it can send misleading information to the electronic control unit, which may unnecessarily turn on the fan based on that.

In other words, the fan may end up coming on despite the engine being cold.


Also known as “ECU”, the ECM is the computer that monitors the sensors of your car to trigger their corresponding functions accordingly.

This ensures that the car runs smoothly without any problems. For starters, ECU and ECM stand for “Electronic Control Unit” and “Electronic Control Module,” respectively.

Now, if the electronic control unit or electronic control module has gone rogue, it may turn on the fan even though the engine is cold or contrary to your expectations.

Just like a normal computer, the ECU/ECM can get corrupted by a virus because it relies on software code.

Solutions for the Above Causes

  1. Turn off your climate control system if it’s the culprit.
  2. Replace the coolant temperature sensor if it’s faulty and misleading the computer to turn on the fan even though the engine is not hot.
  3. Repair or replace your electronic control unit/electronic control module if you establish that it’s what’s causing your fan to come on despite the engine not being hot.

How Much Does It Cost To Fix These Problems

  1. Climate Control System

The good news is that you won’t need to spend money to resolve the problem if it’s caused by your turned-on climate control system. All you’ll need to do is turn it off and the problem will go away.

  1. A Faulty Coolant Temperature Sensor

It costs an average of $491 and $553 to replace a bad coolant temperature sensor. Labor costs are estimated between $92 and $116 while parts are priced between $307 and $320.

  1. A Bad ECU/ECM

The average cost of replacing an ECM/ECU is $900. This is inclusive of the hardware and parts, as well as labor. The average cost of repairing one, on the other hand, is $300 to $750. Again, this is inclusive of parts and labor.

When Should the Car Cooling Fan Come On?

The cooling fan should only come on when the engine’s temperature surpasses the normal operating temperature of 200 degrees Fahrenheit.

The fun should only kick off once the temperature rises beyond this. Usually, the engine is hotter when the car is idling or moving slowly since there’s not enough airflow across the radiator.


Is your radiator cooling fan kicking off when the engine is still within the normal operating temperatures? If yes, it could be an issue with your climate control system, coolant temperature sensor, or ECM/ECU.

The good news is that turning off the climate control system, replacing the coolant temperature sensor, and/or repairing or replacing the computer can help resolve the problem.

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