What Does a Coolant Temperature Sensor Do in Your Car?

What Does a Coolant Temperature Sensor Do in Your Car?

The coolant temperature of your vehicle is essential when determining whether or not your engine needs repairs. The coolant temperature reading should be checked at least once per month. When the coolant temperature drops too low, it could mean that the engine is overheating. This could lead to severe damage if left untreated for long enough. To prevent this, you should keep track of the coolant temperature every time you drive your vehicle.

A coolant temperature gauge will allow you to check the coolant temperature without opening up your hood.

If the coolant temperature has dropped below average, you need to take your vehicle to a mechanic immediately. It may be necessary to replace the radiator or other components depending on the severity of the problem.

What is Coolant Temperature Sensor?

A coolant Temperature Sensor (CTS) is an electronic device used to measure the coolant temperature inside an engine block. It is located at the bottom of the radiator tank. The CTS sends signals to the Engine Control Module (ECM), which adjusts the air/fuel mixture accordingly.

The CTS is connected to the ECM via wires and has a connector plug. The CTS plugs into the vehicle’s electrical system and receives power from the battery.

Location of Coolant Temperature Sensor

The overall design of the car defines the location of the coolant temperature sensor. The coolant temperature sensor is most frequently located on the right side of the engine block or cylinder head. It is installed on the coolant’s inlet plastic hose.

Even in some cars, there are more than one coolant sensors to send the signals for different components such as cooling fan control, dashboard and engine system control unit. In the case of more than one coolant temperature sensor, the sensor transmitting signals to the control unit is often considered the coolant temperature sensor.

 What is the role of the Coolant temperature sensor?

Coolant temperature sensors monitor the coolant temperature inside the engine compartment. The CTS measures the temperature of the coolant and sends this data to ECU.

The ECU uses this data to determine when to open or close the radiator fan. When the coolant reaches a specific temperature, the ECU will send a signal to the fan control module, which then opens the fan blades.

The ideal coolant temperature should be between 195 degrees and 220 degrees.

When the coolant temperature drops below its average level, here are some possible common reasons:

  • A locked fan clutch
  • The engine coolant temperature sensor is turning bad
  • the thermostat is stuck open

When the coolant temperature is higher than the average temperature, some of the possible reasons can be:

  • Closed or clogged thermostat
  • Water pump malfunction
  • Engine running hot
  • A failed head gasket

What are the symptoms of a Bad Coolant sensor?

Some of the prominent symptoms of a Bad Coolant Sensor are:

1.     Poor Idling

The inappropriate air-fuel mixtures due to faulty sensor results in shaking or vibrating engine. Engines are susceptible, and a defective coolant temperature can affect your engine’s health.

2.     Poor Fuel Economy

The faulty coolant sensor transmits a false signal that unbalances the timings and the fuel calculations. The coolant temperature sensor may fail without warning and permanently sends the cold signal to the engine. In this case, even if the engine is hot, the computer mistakenly assumes that the engine is cold, resulting in abnormal fuel use and reduced engine performance.

3.     Problem with Electrical Cooling Fan

In some vehicles, the coolant temperature sensors control the electrical cooling fans. Any fault in the coolant sensor will hamper the functioning of the electrical fan. An experienced mechanic should fix it.

4.     Smoke From Engine

The vehicle exhaust emitting the black smoke is another crucial indicator that the coolant temperature sensor is faulty as the coolant sensor sends false signals to a computer, leading to excessive fuel mixture stimulation. As the chamber cannot burn all the fuel mixture in time, it burns back in the exhaust pipe, emitting black smoke. It is also associated with excessive air pollution.

5.     Check Engine Lights Turn On

Any unwanted development with the sensor signal turns on the ‘Check Engine Light. It will not turn off unless an expert intervenes and resolve the issue.

How often should I check my coolant temperature?

You should check your coolant temperature at least once per month, ideally twice weekly. If you notice that the temperature of the coolant has dropped below normal levels, then you should call a professional immediately.

How to Diagnose the Malfunctioning of Coolant Temperature Sensor?

Although we recommend getting your coolant temperature sensor checked with a certified professional, you can also check it in case of an emergency to identify the root cause.

  1. Check the owner manual to locate the coolant temperature in your car.
  2. Check the repair manual to find the measurement value for the proper coolant temperature readings.
  3. For a sensor with two pins, determine the ohm measure between these two pins.
  4. Now compare this value with the ohm value mentioned in the repair manual.
  5. If there is a vast difference in the value, it reflects a faulty coolant temperature sensor.
  6. However, if the value matches, there could be a problem with sensor wirings or the engine’s control module.

Note: OBD2 is a valuable tool that helps read the data value of related trouble codes.


The coolant temperature sensor is one of the most critical components in the engine system. It monitors the engine’s internal temperature and transmits the correct information to the engine control unit (ECU).

It is essential to keep the coolant temperature sensor working correctly. If the coolant temperature sensor fails, it can lead to issues like poor fuel economy, high emissions, engine overheating, etc. So, it is recommended to have it checked regularly.

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