Diagnosing Electric Cooling Fan Failure – Symptoms & Troubleshooting

An electric cooling fan, also commonly referred to as a radiator fan, is an important component of an engines cooling system. The cooling fan helps keep coolant temperatures down, preventing the engine from overheating. Overheating is a serious problem that can lead to dozens of issues from cracking intake and exhaust manifolds, to blowing head gaskets, to damaging crucial internal engine components like the valves and pistons.

Ultimately, having a properly functioning cooling fan is essential for ensuring engine reliability. However, diagnosing a failing radiator fan can be a bit tricky. And if your fan isn’t working properly there are a number of things that might be the reason for this, making it difficult to pinpoint the reason it isn’t working.

This guide is going to discuss what the electric cooling fan is and how it works and the importance of it on an engines cooling system. Furthermore, we will discuss the symptoms of a bad cooling fan and provide troubleshooting steps to help diagnose the reason it isn’t working. Some older vehicles do have mechanically-driven cooling fans, however, this guide will focus specifically on electronic fans.

How Does an Electric Cooling Fan Work?

An electric cooling fan is also commonly called a radiator fan because it’s primary function is to supply the radiator with air. Coolant flows through the radiator to be cooled down, keeping coolant and engine temps low and within operating specs. The radiator has small fins and air passages in it so that when you are driving outside air passes through the radiators passages, supplying cooler outside air to help cool down the coolant temperatures.

However, when your car is not moving there is no air being passed through the radiator to help it function properly. This is where the cooling fan comes in. The cooling fan, which is a normal blade-style fan will kick on and blast moving air through the radiator to help it keep coolant temperatures low.

When the fan fails it no longer supplies the radiator with moving air which in turn causes higher coolant temperatures and ultimately leads to the engine overheating.

Symptoms of Radiator Fan Failure

• Engine Overheating
• Fan Motor Not Running
• Air Conditioning is Warm
• Check Engine Lights

Engine Overheating

When the cooling fan fails it will prevent the radiator from receiving the air that it needs to adequately cool the engine coolant. This will ultimately lead to the engine overheating. When your engine overheats you will notice the temp gauge is reading very high and you will get an engine warning light for overheating.

Overheating can also be caused by a number of other problems such as a bad water pump, thermostat, low coolant levels, or electrical problems. So overheating alone isn’t enough to diagnose the radiator fan as the problem.

Fan Motor Not Running

The easiest way to tell if the fan is not working is by listening and looking. The cooling fans are powered by an electric motor that makes a whirring noise while it is running. You should also be able to hear the fan blowing air.

If you don’t hear the motor running or the fan blowing then the fan isn’t working. You will have to make sure the engine gets up to operating temperatures before checking this since the fan won’t always kick on immediately when the engine is turned on if the engine is cold.

Air Conditioning is Blowing Hot

In addition to helping the radiator, the cooling fan also works with the AC condenser to remove heat from the air conditioning system. If the cooling fan isn’t working properly it will cause the condenser to become overloaded with heat, causing the air conditioning to blow hot.

Another possible air conditioning related symptom is the air conditioning not running at all. Sometimes you will get an “Engine Hot AC Off” warning light. The AC condenser puts additional load on the engine so when an engine gets too hot and starts overheating it will shut off the AC system to reduce load on the engine to help reduce temps.

Check Engine Lights

If your engine is overheating you will most certainly get an engine light that is notifying you of this. However, there are a number of other check engine lights that you could have. The cooling system has a number of sensors and electrical components that will throw engine codes when they fail.

One of the best first steps in diagnosing engine overheating or a bad radiator fan is to check for any engine codes. This might be able to point you to a sensor or component that is causing the issue with the fan or with overheating.

Causes of Radiator Fan Failure

Understanding the symptoms of a bad radiator fan is important to first diagnose that the radiator fan isn’t working. However, once you figured this out you now have to troubleshoot why the fan isn’t working. Cooling fans are driven by electric motors so the problem could be with the fan itself or it could be with an electrical component too.

• Blown Fuse
• Bad Coolant Temp Sensor
• Fan Motor Failure
• Faulty Fan Relay or Control Module

Blown Fuse

All electrical components in an engine have a fuse. The fuse helps regulate the amount of electricity sent to the unit and is meant to break, or blow, if too much electricity is sent to the component so that the $1 fuse fails and not the $300 cooling fan, for example.

A blown fuse is one of the most common reasons for the cooling fan not working. Fortunately, it is also one of the easiest to fix. Check your owners manual for the fuse box location and fuse number. The fuse box is usually either in the engine bay, under the driver or passenger dashboard, or in the trunk.

Bad Coolant Temperature Sensor

A coolant temp sensor, as the name suggests, monitors the temperature of the engine coolant. As we mentioned previously, the cooling fan doesn’t kick on when an engine is cold but instead kicks on once it has warmed up to it’s normal operating temperature.

Therefore, the cooling fan uses the reading from the coolant temp sensor to determine when it should turn on. If the sensor is sending bad readings to the fan then it might not kick on at all, or in some cases it might always be running and never shut off.

Fan Motor Failure

The electric fans are powered by electric motors. As with anything motor-related or electric, it is prone to failure. An issue with the fan motor will usually require the whole fan assembly to be replaced as the motor is integrated into the fan. However, on some vehicles the moto can be removed and replaced separately.

The easiest way to tell if the motor is the issue is by ticking through the other items on this list and confirming it isn’t a fuse, relay, or sensor related issue.

Faulty Relay or Control Module

A lot of cooling fans also have a relay in the fuse box in addition to having a fuse. Just like a fuse the relay can break which will cause the fan to not work. Additionally, most fans have a control module that controls the speed of the fan. The control module usually sits within the engine bay or is attached to the fan itself. The control module is electronic as well and can fail over time or from dirt and debris gunking it up.

Cooling Fan Failure Summary

An engines cooling fan is one of the most important components for keeping engine temperatures low and preventing the engine from overheating. Electric cooling fans are driven off of the battery instead off of an accessory belt like mechanical fans are.

A lot of things can cause an engine to overheat, or display similar symptoms as a bad cooling fan. Therefore, diagnosing a cooling fan issue requires you to understand where to look and what to check. A bad fan will usually cause overheating, some check engine lights, and cause hot air conditioning. The easiest way to tell if a fan is bad is to listen for it.

Once you determine that the fan isn’t blowing then you must determine why. A cooling fan can fail because of a fuse, relay, its control module, a bad temp sensor, or the fan’s motor itself can fail. Understanding what might cause the fan to fail is important in troubleshooting how to fix it. Ultimately, having a properly functioning cooling fan is important for reliability.