Connect an ohmmeter to the terminals of the sensor. Suspend the sensor in a container of water to heat to heat the sensor. Heat the water and check the temperature with a thermometer and note the change in resistance.

Water Temp Resistance

       12 degrees                                      3030Ω        20                                                  2300Ω
        30                                                  1580Ω        40                                                  1130Ω
        50                                                    860Ω
        60                                                    600Ω
        70                                                    470Ω
        80                                                    350Ω

Water Temperature Sensor

manufactures spec.

Engine Cold 0.5 – 3.4 volts

Engine Hot 0.2 – 1.0 volts

Engine Cold 2000 – 3000 W

Engine Hot 200 - 400 Ω

The ECT we tested met the manufactures specifications.

What type of thermistor is this?

Negative temperature coefficient (NTC) variable resistor.

Explain the internal operation of the sensor?

The coolant temperature sensor has a NTC thermistor with two terminals one for earth and one for power. The ECU supplies a reference voltage 5 volts through a fixed resistor in series with the NTC. The higer the resistance the more voltage is needed to push across the NTC and the lower the resistance the lower the voltage is needed to push across the NTC. So because all the volts have to be used up across the two resistors in series the ECU can then calculate the coolant temperature by compering the volt drop across the two resistors.

Thermo Fan Switch :

Suspend the engine thermo fan switch in a container of water and heat. Check the temperature an resistance plot the temp and resistance on a graph.

Steve Hackett 4826

(CTS) & Thermo Fan Switch (off car)

Water Temperature Sensor

manufactures spec.