The boat has four O2 sensors. Had the same happen my boat on same boat. I bought one new O2 sensor and replaced the starboard post CAT O2 sensor as I assumed that was the one through asking around on internet. Kept getting STBD 19 alarm beeping. I then pulled the pre CAT O2 starboard sensor. It was quite worn. I cleaned up the old starboard CAT 2 (it was dirty, but in decent shape) and put it in starboard pre CAT. I ran Cataclean through the engine via gas treatment as well. After a 2 or 3 engine start up cycles the alarm went off. Been good ever since (3 years) There is a diagnostic port behind the cockpit, mine has 4 junctions right in the middle of the area when you open the panel. I can connect a rinda techmate tool at that spot. There is also a harness on the bow side of the engine to connect to. Rinda tool is pricey, had to buy a harness for my engine as well. I thought it was worth it, because anytime something alarms on these newer boats and you want to go to the marina, it is abut $100 to hook up and get a reading.....