oxygen sensor

I just purchased a 2011 sundeck 240 with 5.7 mercruiser. Only 60 hours on the engine. I previously owned a 1999 sundeck 210. 700 hours on the mercruiser 5.0 without a problem. First time boating in the 240, I got an engine alarm that there was an exhaust issue, and something about a bad oxygen...

I have a 2011 270SLX with the 8.2 HO engine. Cruising the other day my engine alarm went off and said it was the exhaust system and that it was the oxygen sensor. The boat is brand new and the dealer is coming to look at it. Any idea what caused it to go off and if it was something i did while...