Most modern vehicles use electric cooling fans to help pull air through the radiator so that it can keep the engine cool. Most cooling fans use electric motors that have a moderate to high current draw, and as a result are commonly controlled using relays. The cooling fan relay is the relay that controls the engine’s cooling fans. When the correct parameters are met, a temperature switch or the computer will activate the relay, which will allow power to the fans. The relay will usually be activated once it is detected that the vehicle’s temperature approaches excessively high temperatures. Usually a faulty cooling fan relay will produce a few symptoms that can alert the driver that service may be required.

1. Engine running hot

One of the first symptoms commonly associated with a bad or failing cooling fan relay is an engine that runs hot or overheats. If you notice that your engine is running at higher temperatures than normal, that may be a sign that the relay is not functioning properly. If the relay shorts or fails, it will not be able to supply the power for the fans to operate and keep the engine running at normal temperatures. Abnormally high temperatures can also be caused by a variety of other problems so it is recommended to have the vehicle properly diagnosed to be sure of the problem.

2. Cooling fans do not function

Non-functional cooling fans are another common symptom of a potential problem with the cooling fan relay. If the relay fails, it will be unable to supply power to the fans, and as a result they will not operate. This can lead to overheating, especially when the vehicle is at a stop, where there is no forward motion by the vehicle to pass air over the radiator.

3. Cooling fans stay on at all times

If the cooling fans are staying on at all times, this is another (less common) symptom of a possible problem with the cooling fan relay. If the relay shorts internally, it may cause power to be permanently switched on, which will cause the fans to run at all times. Depending on the wiring setup of the vehicle, this may cause them to stay on even when the vehicle is off, which will drain the battery.

The cooling fan relay essentially functions as the switch for the engine’s cooling fans, and is therefore an important electrical component of the vehicle’s cooling system. For this reason, if you suspect that your cooling fan, or relay, may possibly be having issues, have the vehicle diagnosed by a professional technician, such as one from YourMechanic. They will be able to look over your vehicle and replace your cooling fan relay if necessary.

This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Cooling Fan Relay and was authored by Ed Ruelas.


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