When I start the Yanmar 4BY180 engine on my 2008 36' trawler the Check Engine light and buzzer continue 'ON' until the coolant temperature reaches 122F, at which time I shut her down and restart and everything is fine. Coolant temperature and oil pressure are all normal, and i have been driving with this situation for over a year. No other issues with the engine or the boat.
Does anyone know what could be the problem?
My first guess would be the temp sending unit, its also the logical sarting point for testing. Pull it and test it. If its OK then work your way up the chain from there.
Often problems like this are as simple as a corroded connection somewhere along the way.
It also could be contact points in the sending unit sticking when started and the heat of the engine helping them to separate when the engine is stopped. It could also be a faulty relay.