P0440 on a 2002 cadillac DTS

Question

how do you diagnose service code P0440 on a 2002 cadillac DTS

Answer 1

P0440 Evaporative emission control system malfunction

When this code set  for a Cadillac the EVAP system is not able to maintain vacuum, 2 area that can cause this a purge valve that does not open to create the vacuum from its intake manifold source , or the fuel tank pressure (FTP) sensor does not report the correct fuel tank pressure

 The first step to diagnose P0440 would be to start with purge valve. One side  recieve manifold vacuum. When this solenoid is commanded on it allows the fuel tank to have a vacuum for a calibrated amount of time. Once this purge valve is commanded closed the EVAP system is sealed, and the FTP then monitors the vacuum level if the vacuum level decrease too soon it sets P0440.

 Fuel caps, here a faulty fuel caps with it seal being worn.