How do i fix a gas gauge that goes empty on the halfway mark for a 1999 Plymoth grand voyager?

if the tank is truly empty when the gauge reads a half a tank, then the sensor in the tank is the issue more than likely OR you have a short to limited power. if it goes to a half a tank then sits there for a long time, id look into that but if it goes to the half way mark then dies shortly after, the sensor is the problem.