96 sl2 coolant light

I have a 96 Saturn sl2 The coolant low light keeps blinking and the resevoir is 3/4 full. What could be the problem? Have only had 3 mo. have done oil change.

There is a sensor in the bottom of the reservoir. When it gets dirty, it sticks and fails to work properly thus yielding a low coolant light. Take it off and clean it out with detergent. You may even want to put some uncooked rice in there to help loosen the crud but ensure it all gets out. After thorough cleaning, reattach, fill to specs and see if the light goes out. If not, the entire tank needs to be replaced.

Ensure you start this cleaning process on a cold engine for a variety of reasons.