Welcome to iBoats! Volvo made many different engines in 2015 and just because the boat is a 2015 doesn't mean the engine is.
The engine serial number is the best way to determine what engine you have and what those codes mean.
What tool are you using to to read these codes?
Our local boat dealer pulled the codes, not sure with which tool. I attached the details.
I believe you put in another post that if you have analog meters, the SPN 697/698/699 could be ignored. We have analog meters, but the speedometer has a small LCD reading. Every meter reports normal range function.
Additional context to this is that we only get the CEL and alarm at about 30mph. The boat starts fine, runs great, no limp or guardian mode.
Our local dealer held the boat for a while, chased the codes, and concluded it was most likely the ECM, but everyone I’ve spoken with doesn’t seem to think the ECM is bad.
I did more research on the “previously active” codes and found the 924 to be a probable issue. Someone in another Volvo or Cobalt thread reported the exact issue. Said new knock sensors?
Also reading more and more, it also sounds like it could be a misfire.
The alarm started last season as our batteries were about done. They eventually died so we replaced both. Since replacing the alarm still sounds but only in that 30mph range.
We have another mechanic looking into it.. checking
-spark plugs
-alternator belt tension
-ground connections
-knock sensors (new mechanic just texted and said both show no voltage)
-fuel