GM Temperature Sensor Chart

[Fierofool]

Many of us have had the Coolant Temp Sensor or the Temp Gauge Sensor fail on us, and when replacing it, found that the replacement sensor was also inaccurate.  Here's a chart that gives the resistance values at a wide range of temperatures.  It's best to have the sensor at ambient temperature instead of fresh off the engine. 

It can be used when you pick up a new sensor, too.  Take your multi-meter with you and try to determine the room temperature inside the parts store.  Set your meter to Ohms, and see what resistance you get.  It will tell you what it thinks the room temperature is. 

For example, I have a Temperature Gauge Sensor that I recently removed from my 87.  The temperature in the house is 77.  The resistance tells me that it's just over 90 degrees.  Wish I'd had this chart before I did all the swapping and returning of the Borg Warner units I got from Advance.

This is for any GM sensor that reads temperature. 

The chart was developed by Pennocks member Dodgerunner.

[Fiero GTB]

WHERE do you guys FIND this kinda stuff?  Info like this is worth its weight in gold! Tim

[Fierofool]

I got that from a discussion thread on Pennocks.  Someone had posted it and I saved it to one of my files.  Figgered it'd come in handy some time since it seems lots of people are having problems with their sensors, and the new ones tend to be of poor quality.  I think that if this chart is used, it will save a lot of headache and misdiagnosis. 

Before finding this chart, I returned several new but defective temp sensors.  Every time I had to warm the engine to operating temp to check for accuracy, then let it cool off to remove and return it to the store.  I verified they were defective by installing a used one which was known to be accurate.  This is especially useful on the Fiero Air Intake Temp sensor in the filter canister, the Coolant Temperature Sensor, and the Temperature Gauge Sending Unit. 

[Fierofool]

Just thought I'd bring this one back up to the top to make it easier to find, since some are having problems with temperature and senders, lately.

[GTRS Fiero]

I must be doing this incorrectly.  The temp gauge in my Fiero has been reading constant, ever since I got my Fiero back.  Basically, the gauge reads below the lowest line, until you turn the key, at which point it reads about 1/4, until the key is turned off.  Engine temp has no impact.  Today, I got out the MVM, set it to 29K ohms, put the common lead in the common hole, and the positive lead in the ohms hole.  It read 1.  Then I tapped the lead ends together, and it zeroed the meter. So far, so good.

I pulled the temp gauge connector, and tested with the meter by putting one lead on each pin.  The meter stayed at 1, except briefly, when I may have tapped the leads together.  This is a 2-year-old sensor.

No worries.  I got a new temp gauge sensor.  Same result.

What am I doing wrong?

[Fierofool]

The ground lead should be in contact with the base of the sensor.  Only one terminal of the sensor will give you a reading, and that one is for the gauge.  The other is for the light and won't come on unless the temperature is above 235.  I think the light terminal is the one nearest the slot in the side of the sensor head. 

The test is best done with the sensor removed from the engine.  That way you can better determine the temperature it's sensing, and thus a better reading. 

Your gauge needle should point to the bottom of the thermometer symbol when there is no power applied.  On a cold engine this time of year, it should move to the 100* mark when the ignition is turned to the ON position without starting.  If it doesn't, do both, the needle has slipped.  If it meets the first check with ignition off but not the second check, you have a bad sensor or circuit.

[GTRS Fiero]

The needle does not do both, but it does not increase with temperature, either.  There seems to be a circuit issue.