Is your engine overheating, even when it’s not too hot outside, and you haven’t been driving all day long either?
Is the check engine warning sign also lit on your dashboard?
Well, it could be the Engine Coolant Temperature (ECT) sensor that’s causing these issues.
In this article, we’ll cover what a coolant temperature sensor is, the main signs and causes of its failure, and how to diagnose and fix it. We’ll also answer a few FAQs related to the ECT sensor.
What Is an Engine Coolant Temperature Sensor?
The coolant temperature sensor measures the temperature of the engine coolant through a resistor circuit. It conveys this reading to the Engine Control Module (ECM), also referred to as the Engine Control Unit (ECU), which acts as the “brain” of your car.
How is it done?
The ECM supplies the sensor with a constant reference voltage of 5V which the sensor converts into a suitable voltage signal according to the coolant temperature.
Your car’s coolant temperature sensor usually has a Negative Temperature Coefficient (NTC), which means its resistance decreases with a rise in coolant temperature, resulting in a reduced voltage output signal.
The ECM detects a change in the voltage signal from the sensor and uses it to control:
- Fuel injection and mixing
- Ignition timing
- Variable valve timing
- Transmission shifting
- Radiator fan
- Dashboard temperature gauge
Your car’s cooling system may have multiple coolant temperature sensors, with the primary sensor located on the engine block near the thermostat housing or the radiator.
Now let’s discuss the eight signs of a faulty sensor that can take a toll on your car’s engine performance.
8 Signs of a Faulty Coolant Temperature Sensor
Here are the key symptoms that accompany coolant temperature sensor failure:
#1. Check Engine Light.
One of the first signs of all coolant temperature sensor symptoms you will probably notice is that the check engine light will show up on your dashboard.
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.
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 more fuel will heat the engine quickly.
This will cause the fuel economy to drop and decrease the engine’s performance.
#3. Electrical Cooling Fans not coming on.
Some cars use the engine coolant temperature sensor to control the electric cooling fans. In most cars, you have two separate temperature sensors for the fans, a dashboard gauge, and engine management.
However, if your car has a single sensor, a bad engine coolant temperature sensor may result in your fans not starting.
#4. Black Smoke from the Exhaust Pipe.
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. Hard Start Condition.
The amount of fuel getting injected into the engine is critical at the moment you start your car. If the air-fuel mixture is faulty, you might find your car difficult or impossible to start.
#6. 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 have a separate coolant temperature sensor for the fan, but many cars use the same sensor.
#7. Poor Idling.
Due to a faulty ECT sensor, the fuel mixture will adjust. This will cause the engine to vibrate or shake when the car is at low speed and lead to other power losses and strange behaviors.
The engine is very sensitive 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.
#8. Poor Engine performance.
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 has been before, it may be due to a faulty engine coolant temperature sensor.
5 Common Reasons a Coolant Temperature Sensor Goes Bad
Listed below are the leading causes of coolant temperature sensor failure:
#1. Age and wear.
One of the primary causes of coolant temperature sensor failure is the natural wear and tear that occurs over time.
As a vehicle ages, the sensor can deteriorate due to exposure to extreme temperatures, vibration, and chemical reactions within the engine coolant.
The sensor’s internal components can degrade, resulting in inaccurate temperature readings or complete failure.
#2. Contaminated Coolant.
Contaminated coolant can adversely affect various engine components, including the coolant temperature sensor.
Contaminants such as rust, debris, or air bubbles can build up around the sensor and interfere with its operation.
This interference can cause inaccurate temperature readings, causing the engine control unit (ECU) to make inaccurate adjustments to the fuel-air mixture.
#3. Electrical Problems.
The coolant temperature sensor relies on a strong electrical connection to function properly.
Corrosion, loose connections, or damaged wiring can interfere with the electrical signals between the sensor and the ECU. These problems can result in erratic temperature readings or complete sensor failure.
#4. Excessive heat or overheating.
Operating an engine at excessively high temperatures can accelerate the degradation of the coolant temperature sensor.
Overheating can be caused by a malfunctioning cooling system, a sticking thermostat, or low coolant levels.
Prolonged exposure to elevated temperatures can cause thermal stress on the sensor, resulting in premature failure.
#5. Oil Contamination.
In some cases, oil contamination can affect coolant temperature sensor performance. A leak in the engine that allows oil to mix with the coolant can degrade the sensor.
Oil deposits can coat the sensor, isolating it from the coolant and causing inaccurate temperature readings.
How to Diagnose a Coolant Temperature Sensor Issue?
A mechanic will check your car’s coolant level before going ahead with a thorough test using a voltmeter. They’ll also check the error codes, if there are any, using an OBD scan tool.
Here are the steps they’ll follow next:
- Connect the voltmeter’s positive lead to the sensor’s signal terminal and negative to the chassis ground.
- Cold start the engine and check the readings. The reading should be between 3V – 4V, depending on the engine’s temperature.
- Let the engine get warmed up to its operating temperature. The voltage reading should drop (for an NTC sensor) to 1.2V – 0.5V.
- If the voltmeter reads 5V, it implies an open circuit. They’ll check:
- Signal terminal connection
- Sensor’s ground contact
- If it reads 0V, this indicates a short circuit or no power supply to the sensor.
- Check the connecting wires from the ECM to the sensor
- Check the power supply and ground connection for the ECM
- If the voltmeter still reads 0V, the ECM can be faulty.
If the voltmeter’s readings are beyond the range prescribed above for a cold and hot engine and there are no connection problems, you’ll have to get the sensor replaced.
Let’s get to how that’s done.
How to Replace an Engine Coolant Temperature Sensor?
Here are the steps a mechanic will take to replace the sensor on your car:
- Let the engine cool down for about 15 minutes to avoid any burn injuries.
- Locate the coolant temp sensor on the engine block (near the thermostat housing).
- Place a draining pan under the car. Coolant may leak out after the sensor is removed.
- Carefully detach the wiring connector from the sensor terminal.
- Unscrew the old sensor.
- Screw the new sensor in the clockwise direction. Tighten it using a torque wrench in the clockwise direction as per the manufacturer’s specifications.
- Reconnect the connector back to the sensor.
- Start the engine and let it get warmed up.
- Check the new sensor by monitoring the dashboard temperature gauge to ensure that it reflects the change in engine temperature.
Now we’ll get to the questions that you may have about the sensor in focus.
3 FAQs About Coolant Temperature Sensor
Here are the answers to a few common questions about the coolant temperature sensor:
1. How Much Does it Cost to Replace a Coolant Temperature Sensor?
A coolant temp sensor replacement can range from $70 – $480. The cost depends on the model of your vehicle and the labor charges.
The part costs between $20 – $80, while the labor charges can vary from $50 – $400.
This range does not include taxes and fees, and does not factor in your unique location. Related repairs may also be needed.
2. What Are the Various Types of Coolant Temperature Sensors?
There are three common types of engine coolant temperature sensors:
- Negative Temperature Coefficient (NTC) Thermistor Sensor: These are the most commonly used, and their resistance reduces with a rise in coolant temperature.
- Positive Temperature Coefficient (PTC) Thermistor Sensor: Their resistance increases with an increase in the coolant temperature.
- Two-Stage Coolant Temperature Sensor: It uses two different internal resistor circuits depending on the coolant temperature to improve the accuracy of the voltage signal sent to the ECU.
3. What Is a Cylinder Head Temperature Sensor?
The cylinder head temperature sensor directly measures the temperature of the engine’s cylinder head and is not immersed in the coolant. It’s used along with the coolant temperature sensor in some vehicles or as a standalone sensor on an air-cooled engine.