I digged around a bit. ISA is looking at traffic signs and digital Navi maps to spot speed limits. Thats the reason why nearly every new car now has navigation included. Saw a post of a guy, replacing his media system of his car with an aftermarket system without navigation. This led to speed assist not running anymore. When u block the relevant camera on top, the system should be out (similar to riding in my Audi while snow storm, you get the message "traffic sign detection deactivated")
We will find a solution together guys/girls!

group effort hehe