When testing a temp sender am I measuring the resistance between the body (threads or hex) and one of the terminal pins? When I do that at either terminal I get infinity at any temp, from room temp to 180F. What gives? (BTW, I've tried this on two different new senders and get the same results with two different ohm-meters).

Thanks for any insight you can give me.

There are three devices that measure temperature on the engine. They are

1 - The Temperature Gauge Sender
2 - The Coolant Temperature Sensor (CTS)
2 - The Manifold Air Temperature sensor (MAT)

Notice the difference in Sensor and Sender. The word Sensor is used when the device is an input to the ECM. The word Sender is used with it drives a gauge. (ie oil pressure sender)

The Temperature Gauge Sender has two functions built into one. Shown below is a Temperature Gauge Sender. The pin closest to the side notch is to control the Temperature Light. (YES your Fiero has one). That pin will become grounded to the case when the temperature is above 255

The far pin of the Temperature Gauge Sender controls the gauge. It's resistance can be measured to its case (ground).



The other two devices, the CTS and the MAT, are read pin to pin. Their connectors do not have the side notches. They will always read open to ground. The reason SENSORS don't use the ground as a return is they are used by the ECM and they need to be more precise. Using the engine ground as a return can cause many engine control problems. So instead of using the engine for the ground they have a seperate wire all the way back to the ECM for ground. So thus they need to be read pin to pin.





Temperature Gauge Sender


CTS


The MAT (Manifold Air Temperature) sensor is on the can of the air filter (Yeah, the MAT isn't on the Manifold, go figure). Sometimes it is called different names also like Air Charge Temperature

[This message has been edited by phonedawgz (edited 11-12-2010).]

The manner which you test it depends on which sender you're replacing:

If it's the sender for the ECM (has a yellow and a black wire running to it) then you have to test it with one ohmmeter lead on each pin, not on the body. Given your results, I'd say you probably have this kind of sender.

If it's for the gauge and/or light, then you should get a variable resistance from one of the pins to the casing. The other pin should show infinite ohms to the casing unless you can heat it up to about 257*F (125*C) which is not possible to do with boiling water unless it's under pressure.

Edit: Friggin' Phonedawgz beat me to it by 1 minute!)

[This message has been edited by Bloozberry (edited 11-12-2010).]

Thanks to both of you, especially phonedawgz. That's as sweet a write-up (with pictures!) as I've ever seen on Pennock's.

This is for my 3.4DOHC swap. The motor has a temp warning light sender, but nothing for a gauge. I had nothing to compare it to and assumed the parts store knew what I needed. (I know . . .). They gave me a CTS.

Thanks again, guys. + for both of you.

Note - There is also a combo 3 wire CTS and Gauge Sender available. On that unit the two outside pins are CTS (pin to pin) and the center pin is a Gauge Sender (Pin to Ground)

If you want to use the CTS you have now, you could just attach one side to ground.

Also the pics are not mine, but just stolen/searched pics from other postings/internet

[This message has been edited by phonedawgz (edited 11-12-2010).]

quote Originally posted by phonedawgz: Also the pics are not mine, but just stolen/searched pics from other postings/internet

Still, a lot of work.