its weird how the dealer is not wanting to give the codes out?
i found this online hoep it helps
My 2005, 150 Mercury Optimax started sounding the 4 beep alarm at 2 minute intervals indicating water in the fuel or low oil level. The fuel/water separator did not indicate any water, the external oil tank is full and cap sealed, and I topped of the internal oil tank (run engine with cap loosened). With that, the alarm continues to sound.