Regrettably, you've hit the nail right on the head. These new engines need to hook into the "Mother Ship's" computers to even tell WTH is going on. You've got 2 big "Kids, don't try this at home" engines on your transom.
There is little you can do on the water beyond pulling the cowl and scratching your head, especially when you're out on the water. I keep a pretty nice tool kit aboard the boat, however, few things are specifically for the engine, those being "an emergency pull cord" (115 supposedly could be started by hand), a fully-charged battery pack to avoid even trying to start it by hand, and a piece of copper wire to ream out the "P-tube" outlet when it's blocked so I can be sure the water pump is working.
The only "repair" I've been able to do is a very simple one, replacing the cowl tilt/trim switch which stopped working for "Down", a very easy, 15 minute job. YouTube helps with many small tasks, but most involve hauling out. This was one of the few that could be done at the dock.
BTW, don't forget Yammies are metric...
Now the lecture, the inability to do things clearly demonstrates why you need to keep up with all maintenance done by a qualified technician who has access to all the special tools and the Mother Ship Computer, and to sin on the side of precaution. No matter what, I have my water pump, internal sacrificial zincs, thermostat, etc. replaced every fall during winterization. Even routine winterization should be done by a pro with the computer. Yes, I could change oil/filter, grease things, fog it, etc., but without hooking it up to the diagnostic computer you wouldn't know if there were any readings that might suggest an impending issue.
