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my temp sensor light came on one morning when i first started my car but my temp gauge is running normal. any ideas???

There are two temp sensors. The one that runs the dash is apparently still working, that one is on the back cylinder head. The one that feeds the ECM may be malfunctioning... That is the two pin sensor right in the thermostat housing. I would start with replacing that and see if that fixes it.

The sensor that feeds the ECM will give you driveability and fuel mileage problems too, so make sure to replace it SOON if it is no good.

I wonder how the ECM responds when it goes in the opposite direction though... sounds like its responding as pegged hot and not sub freezing as it usually does. I know yes -40 going to the ecm results in a very rich mixture and bad mileage, but I wonder what would happen if its constantly reading 260 or something.

The dash light usually only comes on with a high temp condition, thats why I'm asking the above. I guess it wouldn't be a bad idea to also be sure that the gauge is reading correctly and thats not the one failing, and the car actually is overheating. But with the above condition happening on first start it leans more toward the ECM sensor.

I forget how they go... Resistance up as temperature goes up? Or vice versa?

Open circuit results in -40 on my MS. So closed circuit would be the other side of the spectrum

Resistance increases with temperature, you are correct.

mine is the quad so i only have one head, so where would the sensor be? and the light is on when i first turn the car on so i know im not really overheating cause my temp gauge has been running the same for years now.

I went off 94 z26 and assumed 3100... My bad...

Hopefully someone can chime in since I do not know exactly where its located.

They are right next to each other, by the water outlet.

ill look when i get home, how will i know which one is which?

And thanks for all the help.

If its the same as a v6 the engine sensor should be a two pin one and the gauge should be a 1 wire one.

3X00-Modified wrote:If its the same as a v6 the engine sensor should be a two pin one and the gauge should be a 1 wire one.

This.

Or if you really arent sure, unplug one and see if your gauge stops working.
Thats about as basic as troubleshooting gets lol. "is it plugged in?" Haha

3X00-Modified wrote:I wonder how the ECM responds when it goes in the opposite direction though... sounds like its responding as pegged hot and not sub freezing as it usually does. I know yes -40 going to the ecm results in a very rich mixture and bad mileage, but I wonder what would happen if its constantly reading 260 or something.

The ecm starts making things rich again when the engine is overheating, so I would assume that it would be a very similar situation - bad mileage and poor performance.

I have the same car as you (94 Quad Z26), here's a pic with the location of the two sensors circled in red, one in the plastic water outlet and the other in the back corner of the head.

the one in the head, is for the ECU, the one in the t-stat housing is for the gauge. if you are still unsure, the one for the gauge will have a square type plug and the ECU one will have a more rounded plug after you unplug them.