Coolant Temperature Sensor 101

Coolant Temperature Sensor 101

Sometimes, it’s the little things that can cause major issues.

What Does the Coolant Temperature Sensor Do?

The Coolant Temperature Sensor is about the size of a baby pacifier yet it is the main component in making sure your engine doesn’t overheat. It’s important job is to measure the temperature of your engine coolant and then send those results to the engine’s computer system or ECU. Depending on the car, the sensor can also be used to turn on the cooling fan when engine temperatures are too hot.

In Chicago, the above process is especially important with our inconsistent weather changes. When the ECU calculates the temperature of the engine from the Coolant Sensor, the ECU uses mathematical data to change the fuel injection or ignition timing. A cold engine requires different timing of fuel intake than a warm engine.

With all of these tasks happening several times a minute, it’s no wonder this little coolant sensor often needs replacing. Many times the coolant sensor will get corroded or will leak coolant through the wiring connector. These are common problems we see in the cars that come into our shop. Though, as the driver it can be very hard to spot the signs of a bad coolant temperature sensor.

Common Signs of a Bad Coolant Sensor

Check Engine Light

The most common sign, as with most engine problems, is the check engine light on your dashboard will turn on. Depending on the type of car, you may be able to read the check engine code to see if it is an engine coolant issue.

Decrease in MPG

Have you noticed that your gas mileage has been dropping? This could be due to a bad coolant sensor assigning too much fuel intake which uses up more gas. If you notice that you are driving the same amount of miles as usual but taking more trips to the gas station, you may need to have your coolant sensor checked. The cost of repairing the sensor could save you more money than the additional trips to fill your gas tank.

Trouble Starting or Black Exhaust

In extreme cases, your car may have trouble starting after the engine has warmed up. You may also notice black smoke coming out of your exhaust. This means that you should get your car serviced as soon as you can before it causes more damage to your engine.


As we mentioned in the beginning, the coolant sensor measures the temperature of your engine’s coolant. If you have a bad sensor, it can often misread the correct temperature which can lead to your engine overheating. Keep an eye on the coolant temperature gauge on your dashboard to make sure you are not experiencing any overheating. See what else could cause your engine to overheat.


Coolant Temperature Gauge

Coolant Temperature Gauge

If you have any questions about your car’s coolant sensor or other problems, give us a call and we will be happy to answer any of your questions. specializes in European auto repairs and maintenance. We strive to keep our service costs 40% less than dealerships. Schedule your next service or maintenance for your Audi, BMW, Land Rover, Mercedes, MINI Cooper, or Volkswagen with us.

Written by Spotlight Automotive