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Symptoms of Bad Engine Coolant Temperature Sensor (ECT)

Posted by on May 15, 2018 | 0 Comments

engine coolant temperature sensorEvery car needs a coolant/antifreeze to keep the engine temperature at an optimal level. But how does the coolant system know if the engine is operating at its ideal temperature?

This is done by the Engine Coolant Temperature sensor, also known as ECT. Any problem with the ECT can cause damage to your car’s engine, thus, it is recommended to fix the issue right away. In this article, we will discuss the symptoms of a bad ECT sensor and how you can take care of the situation.


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.


Bad Engine Coolant Temperature SensorPoor Mileage

Check Engine Light ON

Black Smoke from the Exhaust pipe

Engine Overheats

Poor Idling

Hard Starting Condition

Long cranking times

Faulty Engine Coolant temperature sensor

Faulty Wirings to ECT sensor

Bad connection in plug

Faulty ECM
Replace Engine coolant temperature sensor

Repair Faulty wirings

Clean ECT connector with spray cleaner

Replace/Repair ECM


What is Engine Coolant Temperature Sensor (ECT Sensor)?

Engine Coolant Temperature (ECT) sensor is also known as Coolant Temperature Sensor (CTS) or Engine Coolant Temperature Sensor (ECTS). It is used to measure the temperature of coolant present in the cooling system and provide an indication of how much heat the engine is giving out. The ECT sensor is linked with the car’s ECU and it indicates if the engine is running at an optimal temperature.


How does the Coolant Temperature Sensor Work?

The 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.


What Happens when the ECT Sensor gets Damaged?

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.

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.

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 inspection.

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 a thick black smoke.

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 on-board 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.

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.


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.


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.

If you have any issue replacing the ECT sensor yourself, take your car to an authorized repair shop and have it replaced by a professional. The average cost for the component is between $31 and $58.

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