check coolant level on deville

If you are *sure* that the level is not low, then yes, it most likely is just a bad sensor. Which is not uncommon.

I don't think the sensor is serviceable. I believe you will need to R & R the tank.

As usual, ranger is correct. The sensor is part of the overflow tank, you have to replace the entire unit, I think its around 100 bucks tho, and for the deville, thats cheap. Definetly not something you want to let go, its good to know you have the proper coolant level (2 inches below the top of the tank), especially with a northstar.

The sensor in my Deville has been bad for gawd-knows-how-long...I check the coolant every week, and the level hasn't moved in 23 months, since we did the coolant change in '05. I use a little wooden 6-inch ruler with a mark on it, held level with the top of the filler neck...

I've also never seen the gauge move above the 1/2 mark. Even last summer in Palm Beach FL stuck in construction traffic, AC full blast, about 95 degrees ambient.