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What is the problem you are trying to solve? The ECT is a Netative Temperature Coeficient Thermistor, NTC. Basically it is a temperature variable resistor and since it has a Negative Temperature Coeficient, the resistance gets smaller with increasing temperature. It is a passive electronic device and can not and does not interrupt any voltage, and no it is not hard to generate a constant voltage. The ECT is most likely used in a voltage dividing circuit referenced to ground and as such the voltage at the non-grounded terminal is proportional to the resistance which is proportional to the coolant temperature. Check the 700/900 FAQ for resistance values at various temperatures.
It is not wise to measure resistance values into random ECU pins. It is possible to cause damage if the wrong voltage or polarity is applied to the semiconductor devices therin. I won't even try to explain the risks associated with electrostatic discharge. However the simple advice is. "Don't connect an ohm meter to the ECU". You can safely use the ohm meter to measure the resistnce of the ECT to check if it is working properly.
BTW. If you have a lot of crud/corrosion on the connector, you could be getting false readings. Or if you carelessly probe the connector, you can damage it to the point where it is causing increased contact resistance. If you know or suspect that you have damaged the connector, you should replace it ASAP. Increased contact resistance will cause the temperature to appear colder than actual. (That NTC thing again.)
One final note. Thrmistors are very very reliable, both in the robust sense and in stability. That is the resistance values do not drift with age. i.e. it does not go out of "calibration" after years of service. They are basically a ceramic formed at very high temperatures.
Good luck.
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