engine coolant temperature sensor

Symptoms of a Bad Engine Coolant Temperature Sensor & Replacement Cost

In Coolant by Magnus Sellén3 Comments

engine coolant temperature sensor

A coolant temperature sensor is especially important for the optimal performance of your vehicle.

While you drive your vehicle, the engine goes through continuous combustion. This can make it very hot during the drive, especially during the daytime drive.

To keep the engine cool, there is always a mechanism used in each vehicle to keep it cool usually by passing different fluids and liquids through the engine.

You may already know that overheating can affect the performance of your engine and too much heating can eventually make the engine seize or break down. To keep things cool, the water in the radiator is passed through the pipes to maintain the temperature.

The engine oils are also specially designed to ensure the minimum heat production while your engine runs. That is why it is important to regularly check and fill the water in the radiator through the opening present under the hood of your vehicle.

Signs of a bad Engine Coolant Temperature Sensor

Like every other component, the ECT sensor can also get damaged resulting in a number of engine-related problems. Hence, it is advised to have your car inspected right away to avoid any serious problem. Here are some of the common symptoms you might face if the ECT gets damaged or becomes faulty.

Common symptoms of a bad engine coolant sensors are overheating, hard starting conditions, poor idle, check engine light ON and the electric fans do not work properly. The easiest way is to read the trouble code memory and check the value from the sensor, to make sure it’s a possible value.

1. Poor Mileage

A faulty ECT sensor can send a false signal to the onboard computer resulting in an incorrect fuel pressure regulation. For example, a faulty sensor can send a signal indicating the engine is cold when it is not and as a result, more fuel will be used to heat up the engine fast. This will cause the fuel economy to drop and decrease the engine’s performance.

2. Check Engine Light Activates

One of the first symptoms you will notice is that the check engine light will activate. If the computer detects any problem with the sensor’s circuit, it will illuminate the check engine light indicating that the car needs an inspection.

3. Black Smoke from the Exhaust pipe

Due to an incorrect temperature signal, the ECU may enrich the fuel mixture to a point where the combustion process becomes difficult. The excessive fuel will burn in the exhaust pipe and will produce thick black smoke.

4. Engine Overheats

The cooling fan which is behind the radiator grille removes heat from the engine’s coolant. This fan is electrically controlled and relies on the signal from the onboard computer. If the fan receives a false signal, the fan might not turn on causing the engine to overheat. Some vehicles can have a separate coolant temperature sensor for the fan, but a lot of cars use the same sensor.

5. Poor Idling

Due to a faulty ECT sensor, the fuel mixture will adjust accordingly. This will cause the engine to vibrate or shake when the car is at low speed and give other power losses and strange behaviours.

What is a coolant temperature sensor?

Coolant temperature warning lightCoolant temperature sensors are also known as engine coolant temperature sensors or ECT sensors. The principle working of this sensor involves the use of an electrical resistance which measures the temperature of the coolant. These measurements produce essential data for the engine system of your vehicle.

The readings produced from the coolant temperature sensor are transmitted to the engine control unit, where it is utilized as data for regulating and maintaining the proper ignition time and the optimal fuel injection through the computerized approach.

It is usually placed on the right side of your vehicle adjacent to the radiator. The heat produced as the energy waste due to fuel burning is regulated by the coolant that we use in our vehicle. The coolant temperature sensor plays an important role in monitoring the performance of the coolant and takes measurements of the temperature.

It can help the control unit in your engine system to detect when the coolant is not functioning well and your vehicle is overheating. Hence, the coolant temperature sensor carries out its primary function of alerting the engine system when the temperatures are beyond the standard limits which may damage your vehicle.

How does the Coolant Temperature Sensor Work?

coolant leakThe ECT sensor is usually located somewhere near the engine thermostat. The sensor measures the temperature provided by the thermostat as well as the coolant itself. The recorded temperature is then sent to the ECU which then adjusts the engine functions accordingly.

The onboard computer also opens and shuts down the cooling fan depending on the temperature reading and controls exhaust gas recirculation and fuel combustion process as well.

How to diagnose a faulty engine coolant temperature sensor?

When your check engine light is on, the best way is to start with reading the trouble code memory. You can do it at home if you have an OBD2 scanner. If you do not have one at home, but want one, you can check out our review article about the best OBD2 code scanners. Check it out here.

With a good OBD2 code reader, you can also check the live data and the parameters of the CTS sensor. Check that the temperature value of the CTS is around 80-90c when the engine is hot.

A lot of engine coolant temperature sensors have two wires and the sensor is controlled by Ohm. Get a wiring diagram and get what ohms you should have at a specific temperature to check the function. You can use a Digital multimeter. to check the Ohm between the pins.

The diagnostic procedure for detecting a bad coolant temperature sensor is relatively a quicker task. The diagnosis of the bad of failing coolant temperature sensor involves the following steps:

  1. Locate the coolant temperature sensor in your vehicle by referring to the service manual.
  2. Connect the digital multi-meter to the coolant temperature sensor by connecting the red probe to the terminal end of the coolant temperature sensor and the black probe to the solid grounding.
  3. Note the readings
  4. Start the engine and let it run for a couple of minutes at least.
  5. Note the readings initially while the engine is cool
  6. Keep it running until the engine is hot
  7. Note the readings again when the engine is hot
  8. Find the difference between the maximum reading while the engine was hot and the minimum reading while the engine was cold.
  9. See if the difference between the hot engine reading and the cold engine reading is more than 200 ohms.
  10. If the readings are not more than 200 ohms your coolant temperature sensor has gone bad.

Location of the coolant temperature sensor

Typically, the coolant temperature sensor will be located in the coolant pipe. In most vehicles, this is present behind the right cylinder head below the air intake pipe. Different brands and car manufacturers have a different way to place the coolant temperature sensor depending on the car design. Generally, it is located close within the proximal area or inside of the thermostat off the cooling system of your vehicle.

Some vehicles may have more than one temperature sensors, as sometimes different sensors are used to send the signals to the dashboard and the control unit of your engine system. This is optional and a manufacturer can use only one coolant temperature sensor to send the signals to both of these desired receivers. In the case of two sensors, we usually consider the one sending signals to the control unit as the coolant temperature sensor.

How to Ensure a Long Life-Span of Engine Coolant Temperature Sensor

The Engine Coolant Temperature Sensor can last a long time if it is properly maintained. Here are a few tips which will help your engine stay in good condition and avoid problems associated with the ECT.

Do not Use Tap Water to Refill Radiator

A lot of people make this mistake of filling the radiator with regular tap water. The tap water has elements of rust and other minerals in it which can be harmful to the engine in the long run, especially if the water begins to boil and evaporate inside the radiator. Always use a coolant as it provides proper lubrication and prevents rust formation.

Fix Oil Leaks and Gasket Immediately

If there is a leak in the engine bay and the oil enters the engine block, the coolant will get contaminated causing a problem to the ECT sensor.

Check for Coolant Leaks

The coolant system of the car does not need constant refilling. However, if the coolant level is dropping frequently, there might be a leak and should be fixed immediately. With inadequate coolant in the reservoir, the ECT sensor might give a false reading to the ECU.

Replacing the ECT Sensor

The ECT sensor is located near the radiator usually down inside the engine bay. Once you locate the ECT sensor, disconnect the connector cable which connects the sensor to the ECU. Unscrew the ECT sensor in an anticlockwise direction similar to how a spark plug is removed. Install the new sensor and reconnect the connector cable.

Coolant temperature sensor Replacement Cost

The average replacement cost of the Coolant Temperature Sensor is between $100 and $220. The labour cost is between $40 and $140 while the part itself cost between $50 and $80. The coolant temperature sensor is relatively less expensive compared to many other sensors installed in your vehicle. On average for most vehicles, the cost for the parts involved in the replacement of the coolant temperature sensor was from $55 to $80.

However, the lower end of the coolant temperature sensor price was as little as $36, while the higher end of the coolant temperature sensor parts price was as much as $90. It is important to note that the price can get higher than this in the case of luxury vehicles.

The average labor cost involved in the replacement of the coolant temperature sensor is anywhere between $40 and $140. However, it is a highly variable factor, and the labor cost in certain cases can be higher than $140. It is a good idea to get different quotes, do market research and bargain for the just and right price of the work with the mechanic if you are trying to save up on the cost involved in it. Otherwise, you may also try to go for a do it yourself replacement as it is relatively easier and simple as described in our guide.

Replacing a coolant temperature sensor

Here is a step by step procedure to replace the coolant temperature sensor of your vehicle. Remember that all car models are different, and this is just a general guide of how to do it.

  1. Get the tools that you may need and get the protective wears.
  2. Keep the service manual of your vehicle with you before you get started
  3. Make sure that your vehicle is parked on the straight flat level surface.
  4. Locate the coolant temperature sensor in your vehicle with the help of your service manual
  5. For clearance and reaching out jack the front end of your vehicle to lift it.
  6. Remove the overflow cap as well as the radiator cap
  7. Drain the radiator of your vehicle by opening either the petcock or the main drain
  8. Put the drain plug back into its original place
  9. Remove all the electrical connectors from the temperature sensor after locating all of them.
  10. Remove the coolant temperature sensor from where it is mounted.
  11. Clean the hole where the sensor is located in order to remove any interference.
  12. Match the old sensor with the new one
  13. Place the new sensor from where you removed the old one
  14. Connect all the electrical connections back from where you took them off.
  15. Make sure once again that you have tightly plugged in the drain plug of the radiator.
  16. Add the coolant in your radiator from the radiator opening.
  17. Add the coolant in the coolant reservoir system of your vehicle
  18. Dispose of the previously used coolant that you drained out.
  19. Remove the jack stand from the front end fo your vehicle.
  20. Start the engine and warm it up.
  21. Make sure once again that there is no leaking from anywhere
  22. Verify if the check engine light is turned on
  23. Verify if the low coolant indicator light is on.
  24. Take a drive to test your vehicle
  25. Check the coolant once again after 1 hour of drive and fill it back up to the mark if it goes down.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

  1. Honda Civic 1996-my radiator fan automatically run when i ON my start. whats the probable cause?

  2. I am in the UK & have a 2015 Seat Leon 1.4tsi 150bhp car. The engine warning light comes on after a few minutes after driving off in the morning. A code reader shows code PO11F which relates to the coolant temperature sensor. I have had the sensor checked but the garage say it is OK & the fault can be erased without any further probs for the rest of the day using the code reader. But it does come back the next morning if I drive straight off from cold
    I have discovered by (accident) that I can prevent the warning light coming on simply by starting & then stopping the engine within 30 seconds in the morning before driving off & then it is OK for the rest of the day. I have no overheating problems & otherwise car runs great.
    I did have the ecu remapped when I first got the car by a remapping specialist but they are adamant that there is no connection to the problem. But now I am wondering if that is the cause. Has anyone any ideas please..

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