STOP and engine symbol flash with icy (!) running engine

Hello together, as it says above: this morning the ice-cold (!!!) Vivaro started and wanted to drive off, the STOP and the engine symbol flashes. I then turned off the engine and restarted after a few seconds. Same result. In the guide is the following: Quotation: Switching off the engine (STOP) lights up together with (MOTORSYMBOL) when the coolant temperature is too high. Turn off the engine immediately and use the help of a workshop. Too high? With a 12 hour cold engine in winter at 4° outside temperature? But probably not!? Can it be that the coolant sensor is defective instead? Unfortunately, I don’t know about cars at all, but I just opened the hood and checked all the visible containers, everybody is on MAX (oil between MIN and MAX). Tonight my buddy comes by with his OBD diagnostic device, let’s see if there’s anything out of it. If it’s the coolant sensor s Should, can you change it yourself? Where is the Vivaro? Thank you for your help.