Interesting, I just went through the exact issue with our Cummins powered 09' classic three weeks ago. Out for a morning coffee cruise and alarm goes off showing code 155, high IMT. Sure enough was reading 205 underway and cooled back to 175 as powered reduced. After sitting overnight, Smartcraft reading was still 175. Did a search on Tugnuts found several threads on this topic and sure enough appeared to be sensor driven. Thanks to Dan on Northern Focus for posting the Bosch sensor part number, $30 vs I am guessing over a $100 from Mercruiser. After reading the threads I had what appeared to be to be 2-3 hours (or longer) involved to change out the sensor. Not the case! I decided to leave it with our marina mechanics and the young man who came down had it changed in 30 minutes without having to remove any components. 😀 About 6 years back, to make several maintenance tasks easier, I removed the battery selector panel in the cave and enlarged the opening to the point where it would just secure the selector switch panel. He went in through that area. You should be able to press the check mark key to reset and stop alarm from sounding. New sensor, Inlet Temp now reading between 97-105F.
Mike
