Coolant Temperature Sensor

Engine Coolant Temperature Sensor Symptoms, Location & Replacement Cost

In Coolant by 13 Comments

An engine coolant temperature sensor is essential for the optimal performance of your car.

The engine coolant temperature sensor’s job is to measure the coolant temperature for the engine control module.

With this information, the engine control module adjusts the air-fuel mixture depending on the temperature.

In this article, we will discuss the most common symptoms of a bad coolant temperature sensor, location, replacement cost, and how to diagnose it.

8 Bad Engine Coolant Temperature Sensor Symptoms

Like every other component, the ECT sensor can also get damaged, resulting in several engine-related problems. Hence, it is advised to have your car inspected right away to avoid any serious problems.

The most common symptoms of a bad engine coolant temperature sensor are check engine light, poor engine performance, overheating, hard starting condition, and the electric cooling fans won’t start.

Here is a more detailed list of the common symptoms of a bad coolant temperature sensor.

1. Check Engine Light

Check Engine Light

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.

If you see a check engine light on your dashboard, it is time to check the trouble codes with an OBD2 scanner.

2. Poor Mileage

Bad Fuel Consumption

A faulty ECT sensor can send a false signal to the onboard computer, resulting in an incorrect air-fuel mixture. 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 the engine quickly.

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This will cause the fuel economy to drop and decrease the engine’s performance.

3. Electrical Cooling Fans not coming on

Cooling Fans Radiator Car

Some car uses the engine coolant temperature sensor to control the electric cooling fans. You have two separate temperature sensors for the fans, dashboard gauge, and engine management in most cars.

However, if your car has a single sensor, a bad engine coolant temperature sensor may result in your fans won’t start at all.

4. Black Smoke from the Exhaust Pipe

Black Smoke Car

Due to an incorrect engine 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.

5. Difficult Starting Condition

Starting Car

The starting moment of a car is very critical when it comes to the amount of fuel getting injected into the engine. If the air-fuel mixture is faulty, you might find your car difficult or impossible to start.

6. Engine Overheats

Overheating Engine On Road

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 have a separate coolant temperature sensor for the fan, but a lot of cars use the same sensor.

7. Poor Idling

Car Engine Rough Idle

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 lead to other power losses and strange behaviours.

The engine is very sensetive to wrong air-fuel mixtures at idle and this is a condition when you might notice that something is wrong with your engine coolant temperature sensor.

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8. Poor Engine performance

Slow Car Acceleration

As we discussed earlier, the engine coolant temperature sensor can have a hard impact on the air-fuel mixture. A bad air-fuel mixture can also cause the engine performance to drop drastically.

If you feel that the engine performance is not what it have been before, it may be due to a faulty engine coolant temperature sensor.

What is a Coolant Temperature Sensor?

Coolant Temp Sensors

Coolant 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 they are utilized as data for regulating and maintaining the proper ignition time and the optimal fuel injection through the computerized approach.

Coolant Temperature Sensor Location

Coolant Temperature Sensor Location

The engine coolant temperature sensor is usually located on the engine block or cylinder head. It is often installed on a plastic hose on the coolants inlet.

Different brands and car manufacturers have different ways of placing the coolant temperature sensor depending on the car design.

Some vehicles may have more than one temperature sensor, as sometimes different sensors are used to send the signals to the dashboard, cooling fan control, and the control unit of your engine system.

In the case of two sensors, we usually consider the one sending signals to the control unit as the coolant temperature sensor.

Coolant Temperature Sensor Replacement Cost

A coolant temperature sensor costs 30$ to 100$ and the labor costs 40$ to 150$. You can expect a total of 70$ to 250$ for an engine coolant temperature sensor replacement.

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The coolant temperature sensor itself is often quite cheap and you can often find them around 40$ for a quality one. There are cheaper ones on the market also, but I heavily recommend you buying a quality one like Bosch, to skip the headaches in the future.

The replacement is often also quite straightforward, expcept that you might have to pour out all coolant from the engine and refill it – which means that you have to remove all air from the coolant system, which can be difficult.

However, if you are fast replacing the sensor, there is often no need to tap out the coolant, but this requires some skills.

Remember to always make sure the coolant temperature is low when doing this kind of work!!

How to Diagnose a Faulty Engine Coolant Temperature Sensor?

To diagnose the coolant temperature sensor, you need a repair manual for your car model to find what measurement values you should expect from the coolant temperature sensor.

  1. Connect an OBD2 Scanner and look for related trouble codes. Check the live data to see the temperature from the sensor. If it is way off the range, check the wirings, and replace the sensor.
  2. Locate the coolant temperature sensor in your vehicle by referring to the service manual.
  3. Find the coolant temperature sensor and remove the connector plugs.
  4. If you have two pins on the coolant temperature sensor, you can try ohm measure between these two pins.
  5. Check your repair manual for the correct ohm-value at a given temperature.
  6. If the value is wrong – replace the sensor.
  7. If it seems fine, check the wirings and connectors between the coolant temperature sensor and the engine control module.

13 thoughts on “ Engine Coolant Temperature Sensor Symptoms, Location & Replacement Cost ”

  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..

    1. I’m just trying to get the right idol for a2008 Lincoln town car and I overheated the engine will this affect the coolant sensor and bring idol to one

  3. can you please help me i have a problem.

    my car finished water and i see no leaks

    1. Hello. I drive lexus rx 350 2010. My heat gauge remains below C while driving. Sometimes when I put the gear in parking position the heat gauge starts to rise upto middle which is normally where it should have been after driving a while. Again when i start to drive, it goes below C. There are no engine codes. No black smoke. I think I am getting poor mileage.
      Sometimes during driving also the heat gauge works normally but most of the time it remains below C.
      I am wondering what could be wrong? A bad coolant temp sensor may be?

  4. I am Thomas I’m driving BMW-3-Series-E90 so one mrng I was driving to work I noticed the red temperature warning sign and fan was blowing very high so I stopped and checked in the engine the wasn’t actually hot

    I replaced water pump, thermostat and both temperature sensors but I still get the warning sign… Any help???

    ((2005 Chevy Impala 3.4Liter 6 cylinder))
    Car idles rough unless I hit the gas pedal and give a couple revs. Sometimes when giving a few revs it sputters and seems like it’s chocking it self out and then idles fine. Some white smoke comes out of exhaust when giving revs also. Other times when give a rev or two it dies. I have noticed after it spits and sputters or dies. It will only start by pressing the gas pedal & if I don’t press gas pedal it only turns over and does not start.

    (This is about 5days of working on it)
    I have an CanOBD2 hand scanner, the code that came up is p0300 ( random misfire ) So we replaced the plugs & wires , battery & gutted the cat. No change in performance and reset codes.

    Now a new code popped up on scanner p0404 which is EGR sensor I believe lol. Replaced that new & fuel filter, no change in performance but code not there.

    Turned car on , reset codes and new code popped up p0116. Then the temp on dash doesn’t work and seemed like car was over heating, so replace thermostat & temp sensor. Now Car warms up in cabin, temp on dash works and code gone.

    Car is still rough idle and all , like explained earlier. Scanned and a new code popped up p0306, misfire cylinder #6. Gave a couple revs to get it not to rough idle. Turned car off code is not there anymore but p0300 popped up again. And here I am now talking to you. Anyone have advice? Besides burning it to the ground lol.

    1. Replace coil packs.. There is 3 on top of engine.. Also get Ignition Control Module tested at parts store. Usually this test is not reliable for diagnosing. But. If it fails the test you are in luck. Replace it. The rough idle. As well. Check for vacuum leaks. The Intake boot is known to crack around the Intake Temp sensor. And inside the ribs of the boot. Just thoroughly check everything.

  6. I have a 2007 Dodge Charger and the cooling fans wont turn on. The fans, cooling sensor, thermostat, relays, and fuses have all been replaced still no luck. When the AC is unplugged the fans come on but they just constantly runs. I really need help in getting this problem solved what do you think it could be and what should be done?

  7. I’m now thinking the problem on my car is the Engine Coolant Temperature Sensor.

    Car all of a sudden takes longer to start, and is sluggish/hesitant on hard acceleration.

    Symptoms are the same, hot or cold start.

    Although the dashboard temp gauge still works, when I unplug the ECT Sensor this makes no difference to how the car starts/idles.

    Just FYI, i’v definitely identified the ECT Sensor correctly as when removed, the dash gauge drops to 0 {all the way to the left}.

    Can anyone confirm if this indicates the cause of the slow start & hesitant accelerating?

    Iv ordered up an OBD scanner, just as an aside.

  8. My 2015 Toyota Harrier will not accelerate and the gas tank did ha e water and was drained however the check engine light remains on and no acceleration

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