If all levels are still good then it's not leaking anywhere so 99% sure it's the sensor

yea im convince as well for sure

My Monte is an '04 3400 V6.
I started having a "Disappearing coolant" issue around 70,000 miles.
The level in the Overflow Tank kept falling below the MIN mark.
I wound-up having to replace the Lower Intake Manifold Gaskets.
The rot-gut Dexcool Coolant Chevy used caused the flimsy Manifold Gaskets to fail.

I replaced the Stock Manifold Gaskets with FelPro "Problem Solver" Gaskets and flushed that DexCool out of the system ... replacing it with Prestone Concentrate that I mixed 60/40 to deal with New England deep freezes.

yea luckily i dont seem to be losing any coolany, but i will eventually change out those lower gaskets they are known to fail, but believe it or not its the designs of the gaskets not the coolant that makes them fail, all kinds of coolant not just dexcool, if they are left unchecked become harmful to parts

the issue with dexcool and the gaskets are the old original gaskets are plastic, after heat cycles over and over they get brittle and fall apart. the new revised gaskets are now metal to prevent this. also the dexcool if not changed like every 3yrs can cause tons of sludge buildup and also eat away gaskets. so basically the gaskets are junk and if dexcool is not changed regularly its junk as well.

i dont use dexcool as i feel regular green antifreeze has better cooling capabilities and less maintenance then dexcool.

I just replaced my coolant sensor with one from the junk yard.

My first one from there lasted less than a week.

So when I changed this one I stuck my finger in the sensor mounting hole and felt sludge. I cleaned it out and installed the sensor I got from the junk yard yesterday. So far there is no light on.

You can get to the sensor when you take out the passenger side headlight assy.

There is the wire clip around it and is easy to take off. I didn't drain the radiator. Just work fast with removal, put your finger in to check for sludge then put the new one in. :congrats: