Engine coolant Temperature Sensor / On car

Engine Coolant Temperature Sensor

This sensor is also know as CTS (coolant temperature sensor) and THw (thermistor water). This sensor measures the change in coolant temperature. This sensor is generally located on the thermostat housing. This is a NTC (negative temperature co-efficient). this means when the temperature is high resistance is low and when the temperature is low resistance is high. This sensor is very important for cold starts to warm up the engine. The ecu enriches the fuel mixture and etc.

To do our experiment we connected our ECT to a multimeter to read resistance. We dipped it to a bowl of water which was on the stove to heat it up. Also used a thermometer to check the temperature of the water. The resistance decreased as the water heated up.At 20 degrees Celsius we had a resistance of 2.2k ohms and it decreased down to 300 ohms at 80 degrees Celsius. The readings i got is within manufactures specifications.

Water Temperature (degrees Celsius)	Resistance(ohms)
20	2.2k
30	1.8k
40	1.2k
50	800
60	600
70	400
80	300

The ecu has and internal resistor which reads the voltage after the resistor as show on the wiring diagram on the ECT, when the engine is cold there is a high resistance at the thermistor therefore there is a higher voltage drop at the thermistor so more voltage will be needed at the thermistor. Voltage drop at the internal resistor at the ecu is low and a higher voltage at signal is achieved. when the engine warms up there is a low resistance therefore a low voltage drop at the thermistor and a higher voltage drop at the internal resistor in the ecu, so a less voltage goes to the thermistor. The signal voltage is low because more voltage gets used up at the internal ecu resistor.

On Car Engine Coolant Temperature Sensor)

We located the Ect sensor and back probed the supply wire. Connected the multimeter (on DC volts) red probe to the supply and black probe to ground. We turned the igniton on.

With a cold engine we got a reading og 1.835V. When we started the  started the engine, the voltage decreased to 0.802V when the engine was at normal operating temperature. SO i conclude as the engine arms up the voltage at signal decreases.

I have described how the ECt works on top of the page in the off car part with the wiring diagram.

The Ecu gets information from the ect to see if the engine is cold or warm. If the engine is cold the ecu will make the car rich to heat it up quicker. This is done by opening the injectors longer. When the car warms up the engine will look at the ECT and re adjust injection timing.

Things that could affect the Signal voltage at the ecu :

 - Incorrect Reference voltage getting to the Thermistor due to a high resistance on the supply side.

 - Resistance at ground or the ecu having a bad ground. If theres a high resistance on the ground , the signal will have a high voltage which will tell the ecu that the engine is cold all the time.

 - the thermistor not working

Ground Coolant Temperature Sensor

I back probed the ground wire on the ect and connect my multimeter(on DC volts) red probe to the ECT ground and black probe to the battery post. I started the engine.

I got a reading of 0.3mV telling me that the grounding was good. It is very important to check the ground to dignose problems with the ECT. If the ect has a resistance at ground, the signal voltage will be high telling the ecu that the engine is cold. The ecu will then open the injectors longer making the car rich. The engine will suffer from poor fuel economy and bad emmisions.

Things that can cause this are are:

 - loose  grounding connections caused from vibrations and thermal stress.

 - Electrical terminals corroded by coolant

 - Loose ecu ground.

 - Battery terminal corroded not making a good connection with the negative battery post.

The wiring diagram is on the upper part of the page.