A coolant fan switch is a small and very simple switch comprised of typically two wires. This switch is configured to work based upon the temperature of the engine. As engine temperature rises to a specific threshold, the switch is activated powering on the coolant fan. The coolant fan will continue to run until the engine temperature cools down to a specific predetermined level. Once the temperature reaches this cooling stage, the coolant fan will shut off. Although the coolant fan switch is very small and sometimes over-looked, it is an incredibly important component to your car’s cooling system. Think of this switch as the “gate keeper” to the temperature regulation in your vehicle’s engine. There are many other engine systems which are also indirectly affected by the operation of this switch, but in the context of this article we will focus on its relation to the operation of the coolant fan. Several symptoms may point to a bad or failing thermo coolant fan switch.
1. Engine overheating
Engines generate an enormous amount of heat and as a result are subjected to very large temperature swings if this switch does not operate effectively. When this happens, the result can be extremely damaging, resulting in thousands of dollars in engine damage. A common sign of a faulty switch, which can also be alarming, is that the switch will simply not turn the fans on at the predetermined temperature level resulting in engine heat climbing above what it should be in order to run effectively. When temperatures exceed this threshold, many other components begin to fail, in addition to the performance of the engine declining.
2. Check Engine Light comes on
Fortunately, when this happens your Check Engine Light will be on and depending on the model of the vehicle, an additional “engine hot” symbol will also appear in your dash. This is a very critical time to get the car home or to a place where it will not be driven until it is looked at. In other cases, the switch will turn on and stay on well past the cooling temperature threshold, resulting in the fan running even when the engine is off.
3. Broken or shorter signal wire
As mentioned earlier, there are two wires inside the switch. When one of these is broken it can cause them to ground intermittently, which will cause the fan to also work intermittently. When either of the two wires short out, this can cause intermittent operation as well, again resulting in intermittent responses to the fan turning on or off unexpectedly.
Since this is an electrical component, when faulty there is often times not much predictability as to when it works and when it does not. As mentioned above, the thermo coolant fan switch is a very vital piece to your engine’s life and is a very inexpensive part to replace. As such, our recommendation would be to have an expert mechanic from YourMechanic come to your home or office to diagnose the problem.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Thermo Coolant Fan Switch and was authored by Jeff Engstrom.