Engine coolant low light came on and when I checked the reservoir, it was full. What's up with that? Temperature is fine, not overheating. Red light on speedometer on.this is on my 2001 Vanden Plas

 

There is a float in the forward corner towards the engine. It is probably stuck. You can reach in and gently move it up and down to free it. If you find it already up at the top of the small tube it rides on then the sensor itself has gone bad. You can remove it from the bottom of the tank and install a new one. Worst case is the floating piece has gone bad and you need to replace the tank.

 

Thanks, Avern1.