How does coolant temp sensor work?

[stanleyoutdoors]

I ask because I can't figure out what is wrong with my 3EE Tercel. I have tried about everything (see tercel forum). Short story is it's REALLY rich. One of the many things I tried was a new coolant temp sensor, to no avail.

But today, I tried disconnecting the the coolant temp sensor wires with the engine idling (it idles terribly and barely runs at all). It made no change at all. How does the sensor work? Does no signal from it mean cold (give it more fuel)? If so, it could be possible that the wires from the sensor to the ECU are bad.
Thanks

[new echo owner]

When the engine is cold the ECT sensor will have higher resistance, around 2k ohm. As the engine warms up, the resistance decrease. There is a chart with the corresponding resistance to the temperature. This is for a Camry but it works the same for a Tercel, page 356: http://www.camrystuff.com/manuals/Gen3/eg1.pdf . You will have to check the resistance at the ECU to determine if the wiring is good or not, it should have close to the same reading as you would have measuring at the sensor.

N.E.O.

[stanleyoutdoors]

Thanks again, NEO. Based on that, an open circuit would cause the problem i have so I will look into it. But when I think more about it, it should have thrown a code if there was an open circuit, so I'm not real hopeful.

[new echo owner]

You are correct, an open ECT would have set a code beside causing drivability problem.

N.E.O.