Yep thanks Don. Fully understood regarding the ambient temperature - but by concern is that it's a red warning "pull over immediately and switch off engine" rather than just an orange warning "hey dude, your coolant is a little low, check it when you get home" kinda thing!

And the main thing is, when I immediately scanned following the red warning, there were no codes at all in OBD or on the maxidot warning screen.

And Merry Christmas everybody!!!