hey new to forum, I am having an issue with an annoying check engine light on my boat. the boat is a 2015 AR240 Yamaha. The check engine light and alarm will come on immediately after starting the engine in question. it doesn't matter if I disconnect the batteries, leave them for even a day, it will come back immediately after starting the engine. I have taken the boat to a dealership to have them troubleshoot the issue , they even hooked water up to the boat and they told me that it was the port side o2 sensor. I suspected an o2 sensor being the issue before I took the boat there, but what has me puzzled is even if I swap o2 sensor with the other engine, the port side is still the engine light that comes on. any thoughts? my boat has a cat , so I have 2 o2 sensors. I have tried swapping them around. the dealership did clear the codes and told me to bring it to the lake, which I did but the code came back after about 5 minutes of running it. engines both seem to run fine.