Find one of the tanks and look for the sensors mounted on the side. Take a jumper wire and tie the bottom to the top and you should have a full tank reading on the monitor. Usually the resistor pack is what goes bad or the sensors (studs) inside the tank are contaminated and have to be cleaned off.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7