Yes you'd need a marine scan tool and special adaptors for what design ECM you ought to have on the 2011 MPI engine model...(Mercruiser PCM-09) to read more of the issue at hand and to completely clear the fault if so desired.
2008 - Up (PCM-09 catalyst equipped)
Adapter #94027 (will NOT work with Tech Mate PRO Scanner)
2008 - Up (CAN Network adapter for all catalyst equipped engines, also used on many manufacturer's 2008-up engines) Adapter #94029
2008 - Up (Mercury CAN Converter) Adapter #94032 *MerCruiser CAN Converter, used with adapter 94029 to allow connection to 2008-up Mercury 10-pin CAN networks.
https://www.michiganmotorz.com/diagn...rs-p-4259.html
https://www.ebay.com/itm/Rinda-Techn...-/372480229626
The following is an old version scan tool sometimes found on EBay as either new or used,
https://www.rinda.com/marine/mtspec.htm .< Be sure to read and click on,
This tool is no longer in production and has been replaced by the TechMate Pro marine scan tool, see link below:
TechMate Pro Marine Scan Tool < Also found on EBay or buy direct from Rinda technologies.
All that brought up, the fault should stop sounding the warning horn and dash icon as soon as the true issue is resolved either by you getting lucky of replacing the offending part not knowing what the real issue may really be or it fixed itself somehow.
Are you sure the two wire temp sensor is connected back up at the thermostat housing? Should be 1 Yellow and 1 black wire connector....Did the warning horn start before or after replacing the thermostat?
