I found this module in my dash right behind the fuse panel. It turned out to be the low coolant indicator module. The box was covered with sticky goo from being taped to the wiring harness and when I cleaned it up the part number that was rubber stamped on there got erased so I added the label.



The back side:



This is an interesting circuit. U1-E & U1-F are an oscillator that operates at about 5 KHz. The circuit filters this out and applies it to the transistor, which turns on the low coolant indicator lamp. When the low coolant sensor is submerged it basically shorts out the output of the oscillator and turns off the transistor, so the low coolant lamp goes out. The 160K resistor and 10uF capacitor put in a delay of a couple of seconds, which keeps the lamp from blinking rapidly when the coolant is sloshing around the sensor. I think it's interesting that the coolant is the return line to ground for the one wire sensor. None of the components have mysterious GM part numbers, so it should be easy to repair this module.

How 'bout that !?!
First time to see this one.

Here is a schematic for the low coolant relay along with a photo of the board.

FWIW

That's cool. I like the color coding. Did you draw that?

I didn't calculate the time constant. I just guessed based on what I saw happening on the scope.

One thing I noticed: 100M is not a standard resistor value. They only go up to 20M.

I did not make the schematic. A Forum friend did the work for me a few years back when I was trying to sort out my Courtesy Light Delay Module problems and mistook the low coolant relay for the CLDM.

I don't know about the resistor value.

Check for gasses in the coolant. Blown head gasket will cause that.

Will cause what????

A seven year delay!

Blown head gasket.

What are you talking about? Besides being years old, this thread is about the electronic function and construction of the low coolant module. How does this in any way involve a blown head gasket?

OOPS post on wrong thread. LOL