Symptoms of a Bad or Failing Thermo Coolant Fan Switch

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.


Next Step

Schedule Vehicle Engine Cooling Inspection

The most popular service booked by readers of this article is Vehicle Engine Cooling Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Vehicle Engine Cooling Inspection reviews

Excellent Rating

(150,066)

Rating Summary
140,528
5,206
1,056
753
2,523
140,528
5,206
1,056
753
2,523

Joseph

33 years of experience
540 reviews
Joseph
33 years of experience
Hyundai Sonata - AC is not working - Rowlett, Texas
Joseph was very professional and definitely knows his stuff! Highly recommend them unless it’s a hybrid. I also recommend staying away from a hybrid.
Toyota Camry - Control Arm Assembly Replacement (Front Lower Left, Front Lower Right) - Frisco, Texas
Joseph did a great job.

Glenn

21 years of experience
38 reviews
Glenn
21 years of experience
Pontiac Grand Prix - Vehicle Engine Cooling Inspection - Indianapolis, Indiana
Ok

Brock

32 years of experience
28 reviews
Brock
32 years of experience
Hyundai Sonata - Fuel Gauge Sender Replacement - San Jose, California
Showed up early for me and got the job done. First time was wrong part but second time went smooth with the right part.

Joe

43 years of experience
780 reviews
Joe
43 years of experience
Chrysler PT Cruiser - Camshaft Position Sensor - Largo, Florida
wonderful, thank you!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

P0198 OBD-II Trouble Code: Engine Oil Temperature (EOT) Sensor High
P0198 P0198 code definition Engine Oil Temperature (EOT) Sensor High What the P0198 code means This code indicates there is higher voltage than expected in one or all of the circuits involving the EOT system (low oil engine temperature). What...
How to Calculate the Concentration of Coolant in a Car
A car cooling system works to transfer heat from the engine. Check antifreeze level and condition, and mix coolant with water to prevent overheating.
How Do I Look Up What Different Codes Mean?
You’re You’re driving your car and everything is going fine when, suddenly, the Check Engine Light comes on. You head home and get out your trusty code reader. You connect it to the OBD II connection under the dash, and...

Related questions

I have a lighting bolt icon on my dashboard

When you overheated the engine the check engine light came on most likely for the engine is hot and the lightning bolt comes on indicating the throttle limit control is on. This means the engine is in failure mode and...

Can you have a bad PCM but have no check engine light on?

Hello and thank you for contacting YourMechanic. PCM's typically fail for one of two reasons: voltage overloads (often due to a short in a solenoid or actuator circuit) or environmental factors (corrosion, thermal stress or vibration). If water gets inside...

My car has high miles and tonight it began "missing" and the engine does not seem as "smooth" as usual.

Hello. The symptoms you describe can be caused by a wide variety of issues. If the Check Engine Light has come on, then I would recommend retrieving the trouble codes as the possibilities could be many. Issues with the fuel...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com