If a first or first couple of runs for the year I'd suspect just a balky sensor, maybe some condensation, loose connection etc. Especially since it went away. Should be able to pull the connection and maybe spray some contact cleaner in there and put it back together.
I have dealt with a couple of those sensors over the years...as they start to fail you get the codes...maybe a no start and then a final failure...if the connections look good (had any other work done lately?) then I would just replace it...probably available as a std.,GM part but otherwise probably not a real expensive part anyway. Typically located on the front of the motor dead center of the camshaft.
That's usually the first thing we do in aviation is swap parts and see if the failure follows the part. Never really thought about it on a boat since I'm a single engine.
So was there any work done recently on the motor where it would have been disconnected? Check the plug first...then replace the part. There are no moving parts on the sensor so if a good connection, must be on its way out...being on the water with the failure not as bad as an airplane but...
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2018 Cherokee 39RL Land Yacht (Sorry...)
Tony, I do agree to start with sensors. You can always switch between the motors.
Dream 'Inn III -- 2008 400 Express
Regards,
Ian
The Third “B”
Secretary, Ravena Coeymans Yacht Club
https://www.rcyachtclub.com/