Is it true that a fuel pressure sensor starts reading when the tank hits 3/4full

WHAT ARE YOU TRYING TO DO? SMOG? CLEAR LIGHT? WHAT CODE?

fuel pressure works all the time, tank pressure sensor, for evap, may only work below 3/4 so raw fuel isn't drawn into the engine by purge solenoid. you need to smoke check your evap sys, if no leaks are found, it could need a "tank" pressure sensor. fuel pressure has zero to do with p0440 or evap sys.