CUCV low coolant sensor

[Mastiff]

So my CUCV has a low coolant sensor. The truck has had a hard life and much of the electrical is problematic due to corrosion. Anyway, the sensor light goes on a lot, even though the coolant isn't low (the sensor is nearly half way down the radiator). I was hoping someone on here knew how it worked electrically? I checked it's resistance to ground and it's open (infinite resistance) with full coolant. It would make sense to me that it would be open full and closed when low, so +12V could flow through the dash light when low, but this doesn't appear to be the case, since the light is intermittently turning on...

I shined up the connector on both sides and it seems to have helped, but of course I've done this before. And the sensors itself could also be bad...

Anyway, if I just knew for sure how it was supposed to work, that would be helpful.

 

[diesel4me]

A new sensor is about $25--from what I read online the sensor grounds thru the coolant itself,and the wire going to it goes thru the firewall in a grommet with several others near the fuse box,and there are connections along that path that can corrode and affect its readings..

My 6.2 was missing the coolant recovery tank,so I just used an anti-freeze jug to make a replacement--just drilled a hole in the cap,shoved the hose in,filled it enough to submerge the end,and it has worked for 13 years..
My radiator has a habit of having about 3" of "air" in the radiator tank when I check the level,despite the cap being good,it does have a weepy leak at one side of the thermostat crossover ,maybe air gets sucked in there instead of the vacuum pulling the coolant back into the radiator...the level stays well above the low coolant sensor,and the light has never lit up while driving,only when you first go to start it ,it lights up-(to show the bulb is good)...

At any rate,I found if I keep filling the radiator right up full,next time I check it ,it's "low" again,but it has never run hot or overheated running it at that level,and it never drops any lower,or left any puddles anywhere or at other points like the pump weep hole--so I just figured that is where its comfortable and wants to be,and basically ignore it,I do check often to make sure it drops no lower though,so far it has not.

 

[campfire]

So my CUCV has a low coolant sensor. The truck has had a hard life and much of the electrical is problematic due to corrosion. Anyway, the sensor light goes on a lot, even though the coolant isn't low (the sensor is nearly half way down the radiator). I was hoping someone on here knew how it worked electrically? I checked it's resistance to ground and it's open (infinite resistance) with full coolant. It would make sense to me that it would be open full and closed when low, so +12V could flow through the dash light when low, but this doesn't appear to be the case, since the light is intermittently turning on...

I shined up the connector on both sides and it seems to have helped, but of course I've done this before. And the sensors itself could also be bad...

Anyway, if I just knew for sure how it was supposed to work, that would be helpful.

If you unplug the sensor, the light comes on. So it's not flowing 12V directly through the switch. You probably have (had?) corrosion in the connection, which would periodically break the connection, triggering the dash light.