1987 pontiac fiero temp sensor not working (Page 1/2)
Rune82 MAY 25, 09:34 PM
I have replaced the sensor and connector

when grounding the sensor with a pin the guage and light work but the car wont read the sensor

1987 Gt 2.8l V6

[This message has been edited by Rune82 (edited 05-25-2025).]

1985 Fiero GT MAY 25, 09:39 PM

quote
Originally posted by Rune82:

I have replaced the sensor and connector

when grounding the sensor with a pin the guage and light work but the car wont read the sensor

1987 Gt 2.8l V6




By car do you mean the ECM? There's a seperate sensor for the ECM, below the thermostat housing, if you mean the gauges, then if you ground the pins and the light and gauge work as expected, then either the sensor is bad, or you reversed the wires and are sending the gauge signal to the light and the light signal to the gauge, which would make the gauge appear to not work.
Rune82 MAY 25, 09:55 PM

quote
Originally posted by 1985 Fiero GT:


By car do you mean the ECM? There's a seperate sensor for the ECM, below the thermostat housing, if you mean the gauges, then if you ground the pins and the light and gauge work as expected, then either the sensor is bad, or you reversed the wires and are sending the gauge signal to the light and the light signal to the gauge, which would make the gauge appear to not work.


I have tried a known good sensor and im replacing and testing the one just below the distributor

I never saw one near the thermostat housing?

Also its a resistor on both sides does it affect it if its the wrong way around?
Rune82 MAY 25, 10:10 PM

This is the one i have been testing and replaced
1985 Fiero GT MAY 25, 10:39 PM

quote
Originally posted by Rune82:

I have tried a known good sensor and im replacing and testing the one just below the distributor

I never saw one near the thermostat housing?

Also its a resistor on both sides does it affect it if its the wrong way around?



Ok, and what are your symptoms, is it that the gauge isn't working? Or that the ECM doesn't see the right signal and triggers a check engine light for the temp sensor, if it's ECM, it's a different sensor, if it's your gauge, your testing the right sensor. It's not a temperature variable resistor on both pins, that's only the one pin for the gauge, the second pin is a simple on/off temperature switch, like for the fan, to turn the light on and off, if the switch is wired to the gauge, you'll have no signal (like the wire is cut) until it overheats and the switch turns on (supposed to turn the light on, in this instance it would then peg the gauge all the way over past hot). My guess is the wires are swapped, one pin on the sensor should be open (not connected to ground), one should have a resistance to ground, ground the wires individually to identify them, the one that turn the light on should be connected to the open pin, the one that pegs the gauge should be connected to the pin with resistance to ground.
Rune82 MAY 25, 10:45 PM
Im gona go test that real quick

Thats the only symptom the guage only moves when jumping the pins to a ground

Ima go swap the wires and test again
Rune82 MAY 25, 11:24 PM
After swapping the wires the guage sits farther left

But after a 15 mins drive no movement

i tried boiling water and putting a known good sensor in it and still nothing

even tried using a ligher on a third sensor im not sure works or not
Vintage-Nut MAY 26, 10:33 AM
Coolant Temperature Sensor {to the Dash Guage} and Switch {for the Hot Idiot Light}
GM 25036809 / AC Delco 213-71 / Standard TS-168

One connection feeds the coolant gauge and the other feeds the high-temperature warning light.

Schematic


Sensor Temperature vs. Resistance
Rune82 MAY 26, 04:58 PM
Which side of the sensor is which?

Ik which one goes too the side of the sensor is what
Rune82 MAY 26, 07:37 PM
Update

After trying both ways on the sensor and 3 different sensors one being known working out of a iron duke fiero

Still nothing.

I jumped the connections at the sensor again just to confirm the wiring is working when grounding each side one pegs the gauge and the other turns the light on.

Does the sensor ground to the engine block??? should i clean the threads???