480 Port Check Engine alarm

[Larry Hedden]

The port check engine alarm on my 1998 480 Sea Ray (3196 cat's) comes on with bow up at 1500 rpm after about 15-20 minutes running time. It does not do it every time. There are no indications of overheat or any gauge out of balance witht he starboard engine. I shut that engine down and re-start and it may run the rest of the day? Any Ideas. I do not know what sensors to check or where they are located?
Thanks,
SeaEsta