How does the engine coolant temperature sensor ECT work? NTC thermistor vehicle temperature sensors

How does the engine temperature sensor work? Video 2 of 3. The Engine Coolant Temperature ECT sensor is a variable resistor or thermistor. It’s an NTC Negative Temperature Coefficient thermistor where, as the temperature increases, it’s resistance decreases.

Many cars have more than one coolant temperature sensor. In most cars, the primary ECT sensor (ECT sensor 1) is installed near the thermostat in the cylinder head or block or on the thermostat housing.

An ECT sensor is connected to the main computer (powertrain control module PCM or Engine control module ECM or Engine Control Unit ECU). The PCM supplies a reference voltage (typically 5 Volt) and constantly monitors the ECT sensor signal. Based on this signal, the PCM adjusts the engine performance and operates the electric radiator fans when the temperature reaches a pre-determined level.

If the signal from the sensor is missing, or it is outside of the expected range, the PCM turns on the Check Engine light and stores the related trouble code in its memory.

Ways to test the engine coolant temperature sensor

Because the tip of the sensor has to be immersed in coolant, the low coolant level or air pockets inside the cooling system can cause the signal from the sensor to be incorrect. The coolant level always has to be checked first when dealing with cooling system problems. The ECT sensor connector must be checked for damaged pins or corrosion.

Testing the ECT/CHT sensor Resistance: One way is to measure the resistance of the sensor at different engine temperatures and compare the readings to the specifications listed in the service manual.

Measuring the resistance of the Engine coolant temperature (ECT) sensor. The resistance of the sensor can only be measured when the sensor is disconnected from the circuit. The reason is that if you measure the resistance of any electrical component that is still connected to the circuit, the measurement won't be accurate.

The resistance when the engine is cold is about 2,953 Ohm
It drops to 248.5 Ohm after the engine had been fully warmed up.
The resistance specs vary depending on the car.

Checking the ECT/CHT sensor Voltage: Another way to test the sensor is to measure the voltage across the sensor terminals with the ignition on. Measuring the voltage of the engine coolant temperature (ECT) sensor. Checking the ECT sensor voltage. The sensor is connected to the engine computer (PCM). The PCM supplies the reference voltage (typically 5 Volt); another wire is the sensor ground. Both the reference voltage and the ground must be checked first. Since the resistance of the sensor drops as the engine warms up, the voltage drops too.

When the car is cold, 3.96 Volt is an average reading. On a fully warmed up engine the voltage drops to around 0.988 Volt. With the sensor disconnected, the multimeter will show 5 Volt. If there is no voltage, you know that the circuit is either open or shorted to ground. For example, one of the wires in the sensor harness could break or rub against a metal part and short out.

An example of another sensor that measures the temperature is the intake air temperature (IAT) sensor. Readings of the IAT and ECT sensors when the engine is cold. If the car has been parked overnight, the temperature of the engine (ECT or CHT) and the temperature of the IAT sensor located in the intake should be very close.

Diagnosing intermittent temperature sensor problems: If there is an intermittent problem in the ECT or CHT sensor circuit, you can use a scan tool to diagnose it.

Intermittent fault in the ECT circuit. With the scan tool connected, you can monitor the sensor voltage while tapping lightly on the sensor and wiggling the harness and connector. A change in voltage indicates the problem area. Another way is to monitor the ECT temperature.

Disconnecting the ECT sensor will show as -40 degrees on the scan tool.
Why does the ECT sensor show -40°F (-40°C)?: When the ECT sensor is disconnected, the scan tool will show -40 degrees (-40° Fahrenheit equals -40° Celsius). This feature is useful when diagnosing trouble codes related to the ECT sensor. When the PCM sets the trouble code, it also stores the freeze frame which is a snapshot of major parameters at the time of the fault. If the freeze frame shows the ECT at -40 degrees, it means that the ECT sensor circuit was open at the time of the fault. It could be a problem with the sensor itself, connector or the wiring harness.

#engine
#P0118
#enginecoolanttemperaturesensor
#ECT
#coolant
#mechanic
#P0117
#P0115
#P0116
#P0119
#sensor
#faultcode
#howto
#diy
#auto
#automotive
#automobile
#check
#checkenginelight
#help
#codereader
#learning
#free
#fault
#training
#assessment
#car
#cars
#manual
#temperature
#temperaturesensor
#ntc
#ntcsensor
#ptc
#ptcsensor
#voltagedevidercircuit
#resistors
#thermistor
#etc
#g62
#problem
#replacement
#test
#tested
#testing