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

(171,627)

Rating Summary
161,099
5,644
1,174
834
2,876
161,099
5,644
1,174
834
2,876

Glenn

21 years of experience
38 reviews
Glenn
21 years of experience
Pontiac Grand Prix V6-3.8L Turbo - Vehicle Engine Cooling Inspection - Indianapolis, Indiana
Ok

William

34 years of experience
517 reviews
William
34 years of experience
Mazda 3 L4-2.0L - Vehicle Engine Cooling Inspection - Phoenix, Arizona
Earlier than expected! Diagnosed car within an hour and had an estimate for repairs quick

Matt

15 years of experience
111 reviews
Matt
15 years of experience
Jeep Wrangler L4-2.4L - Pre-purchase Car Inspection - Tempe, Arizona
Highly recommend Matt. He performed a pre-purchase car inspection for me. I am not local and the buyer was late meeting him. After waiting a half hour to start the inspection, Matt still performed an extremely thorough review with a long list of identified items, and followed up the report w a call and detailed commentary. Would definitely use him again.

Brian

23 years of experience
658 reviews
Brian
23 years of experience
Ford Expedition V8-5.4L - Oil Change - Jacksonville, Florida
Brian was polite, professional, and did a terrific job.

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

P0846 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch "B" Circuit Range/Performance
P0846 means there's a malfunction relating to the transmission fluid pressure sensor circuit, due to a faulty component relating to the transmission.
P0882 OBD-II Trouble Code: TCM Power Input Signal Low
P0882 means low voltage is coming from the transmission control module circuit, caused by low battery voltage or an open or short circuit.
B2104 OBD-II Trouble Code: Door Passenger Key Cylinder Switch Failure
B2104 trouble code means there's a failure in the passenger door key cylinder switch, caused by a failed component in the switch.

Related questions

Check engine light is on with codes P2063 and P2064
Hello. The codes you are getting are for the exhaust fluid injection system. Most of the time, this is the result of a failure in the fluid sensor. In some cases, the tank and sensor can be cleaned but most...
Oil leaks into coolant & coolant leaks into oil
If the engine is not overheating or running badly, then yes an oil cooler is most likely the issue as it it will allow oil and coolant to mix. Other possibilities are a bad cylinder head gasket or cracked block,...
Car keeps running hot even after i put in a new thermostat
The brown substance coming from the radiator may suggest a more serious problem, such as a blown had gasket. When this happens, the cylinder head gasket between the engine block and the cylinder head fails due to excessive heat. This...

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