On our '04 F150 Lauriat, after replacing the fuel pump, modulator, fuse panel we picked the truck up and is had the the check engine light on. Mechanic did a OBD and said it was emissions. Still took the truck home as we'd been down w/o it for two weeks at that time, it wouldn't start the next day. Jumped it, found bad cells in the battery and replaced it. Check engine light still on. Took the truck back to the mechanic to look further into the issue. Mechanic says it's the Evap Emission Controle System Pressure Sensor and you just can't replace that sensor you have to do the entire module for a whopping $520. We did change the gas cap, disconnected and reconnected the battery and the check engine light did go out. But mechanic says he checked the specific sensor and it is bad so it won't pass inspection when we go next month for that. I read strings that this is possible to eliminate the message and it is still a bad sensor my question, do you really need to replace the entire module at that price?