The other day my windshield washer fluid warning light went on at the beginning of a road trip and stayed on the whole way. Once I arrived at my location I checked the resevoir and I had plenty of fluid. The next time I drove the truck the light was off for about half the trip so I thought that it was just a glitch but then it came back on and has stayed on again. Has anyone come accros this and if so what is it and how can I fix it?