Last trip of the season, water temperature dropping, and the boat's coming out next week. Most owners go straight to fuel stabilizer, fogging oil and the gearcase drain. That's the right list, but it skips the one moment when the engine can tell you the most: warm, freshly run, with a full season of history in its memory. Ten minutes on the dock before you pull it gives you a reference that's worth a lot in April.
The fault memory, as it is
Read it and screenshot every entry before anything gets cleared. A season of fishing leaves traces: an entry for battery voltage from a long day of trolling with electronics on, a thermo switch entry from the afternoon you ran through weed, a sensor that logged an irregular signal once in June. Taken one at a time, each looks small. Together, with the engine hours next to them, they tell you what to look at over the winter.
Clear the memory after you've saved it. Then in spring, anything you find is new, and you know it happened during storage or on the first run.
Hours, split by rpm
The ECU keeps running time in seven bands, from below 1000 rpm up to 6000 to 7000. Write down all seven in the fall. Compared with last year's numbers, they show how the season was actually spent. A jump in the lowest band says a lot of idling or trolling. A big increase at the top end says the boat was run hard, and maybe the prop deserves a closer look. If you service by hours, this is also the number to base the winter service on. The page on reading engine hours by rpm explains the bands.
Warm engine values worth writing down
With the engine at operating temperature, in the water, note what your engine reports. Using the M-JET DIAGNOSTIC app, the list can include:
- Oil pressure at warm idle, and at a steady 2000 rpm in gear if you can do it safely.
- Cooling water pressure at 3000 rpm in gear. If you logged a value after the last impeller change, compare.
- Engine temperature after a few minutes at cruise. Normal is whatever your engine did all season.
- Battery voltage at idle and at 2000 rpm, to see whether the charging side kept up.
- Trim sensor voltage at full down and full up.
None of these need to match a book value. Their job is to be next spring's comparison. An oil pressure that's lower in May than it was last October, on fresh oil, is a much clearer signal than any single reading.
What to do with what you found
If the cooling water pressure has dropped since the baseline, put the impeller on the winter list. If a sensor entry showed up more than once, clean and seal its connector before storage, not after. If the battery entry is there, test the battery under load and look at the cable ends. Winter is the cheap time to fix these, because nothing is waiting on the boat.
Then winterize as usual
Stabilize the fuel and run it through, fog the engine if your manual calls for it, change the engine oil and filter so acids don't sit all winter, drain and refill the gearcase and look at what comes out. Milky gearcase oil is a seal problem, and no scan will show it. Check the anodes, grease the fittings, take the battery home.
Keep the screenshots in one folder with the date. For more on reading the memory, the Yamaha fault code page goes into the entries and their check steps. Next spring you start with a list instead of a guess.
