First check a gas cap is properly installed or has any sign of any wear.
The large leak fault is triggered when after two attempts to pressurize the fuel tank and all associated lines, it fails to hold pressure.In your case small lines from the tank, charcoal cannister, leak Daignosis pump are probably the cause. Check also the small air intake filter from the charcoal cannister. Spiders and the like seem to find their home there. The best way to find your probelm is by using a 'smoke machine'. See yourt local independant mechanic and ask to have a smoke test done on your tank evap. system. He should know what you mean or send you to someone who does. Good luck.