Engine Coolant Temperature Sensor : Specifications, Circuit, Working, Symptoms, Causes & Its Applications

The engine coolant temperature sensor history is rooted in the growth of temperature measurement technology with key advancements in the 19th & 20th centuries. These sensors use extensive RTDs and thermistors within modern vehicles. Thus, an engine coolant temperature sensor, or ECT, was developed for automotive applications. The ECT sensor monitors engine coolant temperature and transmits this data to the PCM or Powertrain Control Module, which utilizes it to change ignition timing, fuel injection, and many critical engine functions. Thus, precise coolant temperature readings are significant for best engine performance, emissions control, fuel efficiency, etc. This article elaborates on engine coolant temperature sensors, their working, and their applications.

What is an Engine Coolant Temperature Sensor?

An engine coolant temperature sensor, or ECT sensor or CTS (coolant temperature sensor) is a small automobile sensor used in a cooling system of the vehicle that monitors the engine coolant temperature & relays this data to the ECU (engine control unit). This sensor measures the coolant temperature to help the ECU determine the operating temperature of an engine.

ECT Sensor Working Principle

The engine coolant temperature sensor’s working principle is to measure coolant temperature by changing its resistance by temperature. It provides a signal to the ECU that regulates engine parameters mainly for optimal performance. The function of the engine coolant temperature sensor is to measure the engine coolant temperature and send this data to the ECU to regulate engine performance. So based on the information on temperature, the ECU will make suitable adjustments to make sure the engine works at its optimal functioning state.

These sensors are normally located close to the thermostat housing or on the engine block. The ECU utilizes the output of the sensor to make sure the engine runs at the best temperatures, preventing under-cooling or overheating, which could lead to damage or performance issues.

Specifications:

The specifications of the engine coolant temperature sensor or ECT include the following.

• ECTs exhibit an NTC (negative temperature coefficient); thus, when the temperature rises then resistance will decrease.
• It is a two-wire thermistor-type sensor.
• Cold engines have high resistance that ranges from 2000 ohms to 3000 ohms at 20°C.
• Warm engines have low resistance that ranges from 200 ohms to 300 ohms at 90°C.
• The cold engine has a high voltage, like 2V.
• The warm engine has a low voltage, like 0.5V.
• The ECU uses the voltage as an indicator of the coolant temperature.
• Its operating temperature normally ranges from -40°C to 185°C.
• Its accuracy changes based on the sensor however, it is normally in a few degrees Celsius.
• Response time is fast.
• It has a customarily sealed connector for durability & resistance to harsh engine conditions.
• The material is a brass sensor body, Fluorocarbon O-ring & PBT 30% GF connector.

Engine Coolant Temperature Sensor Circuit Diagram

ECT is a type of temperature sensor utilized to measure engine coolant temperature, called a coolant sensor. This sensor is located in the engine’s cylinder, which turns ON the cooling fan (or) emission controls.

This sensor generally includes two wires, mainly 5V from the Powertrain Control Module (PCM) and GND, which is connected back to the PCM. So, PCM is a control unit utilized in vehicles that includes two modules, ECM and TCU.

So the coolant sensor circuit with PCM is shown below. Here, the sensor works as a variable resistance device related to the thermistor. Generally, a coolant sensor is a thermistor that changes its resistance according to the change in the engine coolant temperature. Most of them are negative temperature coefficients or NTC types.

Working

The sensor in the circuit is NTC type, so the resistance will be decreased whenever the temperature rises, and resistance will be increased whenever the temperature reduces. So, because of this coolant sensor property, its voltage can be decreased when the engine warms up or achieves operating temperature. In addition, voltage is enhanced whenever the engine is cold.

We know that the 5V wire is connected directly from the PCM to the sensor’s one pin and returns the GND pin reverse to the PCM. Because of the change within the resistance, the voltage supply will be changed and returned to PCM. So, this returned voltage can be utilized by PCM to measure the coolant temperature. Here, the calculation is being provided according to the application within the engine to turn ON the fan otherwise to turn on other emission controls.

Symptoms:

The symptoms of a coolant temperature sensor include the following.

• Non-functional temperature gauges or inaccurate ones can lead to hysterical engine temperatures.
• Fuel injection system breakdown may not precisely calculate the necessary fuel injection amount.
• Black smoke emission or Engine shaking may not precisely determine the theoretical idle speed, which results in unstable idle.
• Increased fuel consumption and reduced power can affect engine performance & fuel efficiency.
• Whenever the engine coolant temperature sensor experiences a short or an open circuit fault, the electronic fan runs at a higher speed.

Causes:

• Several factors can contribute to the ECT sensor failure. So the engine coolant temperature sensor causes include the following.
• The coolant temperature sensor experiences normal wear and tear over time, which can lead to its eventual failure & deterioration.
• Electrical issues can occur with the electrical connections, like loose connections or corrosion which can interfere with the correct sensor functioning.
• If the coolant is utilized within the contaminated engine with rust, substances, or debris, then it causes harm to the sensor and leads to its breakdown.
• These sensors are simply exposed to higher temperatures within the engine section. So, incessant exposure to severe heat or quick temperature changes can cause the ECT sensor to fail or malfunction.
• Fluid leaks or other coolant leaks close to the sensor can expose it to corrosive substances or moisture which leads to sensor breakdown.
• A coolant temperature sensor, in some cases, has manufacturing defects or quality problems that can cause early failure.

Advantages

The engine coolant temperature sensor advantages include the following.

• The ECT sensor provides precise engine coolant temperature readings which controls the ECU to make required optimal performance adjustments.
• It provides better fuel efficiency by optimizing ignition timing and fuel injection depending on engine temperature.
• This sensor makes the engine run smoothly by providing better performance.
• It alerts the ECU to possible overheating problems by activating the radiator fan & other cooling temperatures.
• This sensor can also help to ensure the engine works in optimal conditions, mainly to avoid damage to system components.
• It provides real-time data on different parameters by allowing for troubleshooting & proactive maintenance.
• The sensor detects potential cooling system problems earlier by allowing proactive protection and decreasing the possibility of expensive repairs.
• It provides the information that the dashboard gauge utilizes to display the temperature of the engine by allowing car drivers to check the operating temperature of the engine.

Disadvantages

The engine coolant temperature sensor disadvantages include the following.

• Some ECT sensor outputs may be non-linear across a broad temperature range that needs compensation & calibration.
• Some ECT sensors can experience self-heating because of the electrical current supply throughout them, which potentially leads to incorrect readings.
• These can be fragile and vulnerable to harm from extreme temperatures or vibrations.
• Its cost may vary based on the quality.
• A faulty sensor sends incorrect temperature readings, which leads to wrong gauge displays & masking potentially overheating problems.
• If this sensor fails to notice a higher temperature, then the cooling system may not work correctly which leads to potential damage and engine overheating.
• It affects the emission control system of the engine which potentially leads to high emissions.
• A faulty sensor causes the radiator fan to work incorrectly, either not turning on at all or running constantly, which can lead to overheating or cooling problems.
• A faulty sensor leads to decreased engine performance and power, because the ECU is not getting precise temperature data for optimizing engine operation.

Applications

The applications of engine coolant temperature sensors include the following.

• The engine coolant temperature sensor monitors engine coolant temperature. So it sends this data to the ECU by allowing it to regulate engine parameters for best performance, emissions control & fuel efficiency.
• The ECU utilizes the ECTS information to regulate fuel injection timing by ensuring the proper fuel amount is delivered to the engine depending on its temperature.
• The ECTS helps the ECU to decide the best air-fuel mixture for resourceful combustion and decreased.
• The ECTS signs the ECU to trigger or disable cooling fans & other cooling system components to avoid overheating.
• The ECTS is an important component in the OBD system, so it allows the computer of the car to observe and examine associated potential problems with engine temperature.
• By keeping the car engine at the correct temperature, this sensor helps in ensuring whole and extremely efficient combustion, decreasing dangerous emissions.
• It helps in recognizing potential problems before they turn into severe ones by checking the temperature of the engine, which allows timely maintenance and & avoids expensive repairs.

Thus, this is an overview of engine coolant temperature sensors, their working, and their applications. This is an ECTS that measures coolant temperature and transmits a voltage signal toward the PCM (Powertrain Control Module), depending on its resistance. So, it changes through temperature by allowing the powertrain control module to estimate and check the coolant temperature. Examples of ECT are the GM coolant sensor and the Ford coolant sensor. Here is a question for you: What is a thermistor?