2003 Jeep Cherokee temperature gauge

Temp gauage was flucation use scan said ect sensor was bad replaced but still have same problem took to garage they put scan on read same code PO117. They tool me engine wans't overheating problem is tem gauge they would have to replace insterment panel cost 500 to 700 hunder dollars would anybody have and other ideas. Just to try. To give more info engine light comes on tem gauge goes from 100 to 260 back and forth then after time which could be 20 minute to maybe 45 minutes gauge woul settle were it should but engine light would still stay on this may last for 24 hrs then same thing car has no problems running