Cooling water symbol lights up 10 sec. after the start

Hello, everybody.

I have a little problem and I'm afraid I'm guilty myself. I tried it once and expanded the speedometer. I soldered it all over. Since then, a lot of things have been working again like, for example. the consumption indicator, range and speedometer also over 140 km/h. Now I have the problem with the cooling water symbol. After the start there is no light in the display, then after approx. 10 sec. lights up the cooling water symbol, accompanied by a warning page.
Does anyone have the circuit diagram of the instrument cluster?
I've been watching the hell out of soldering, but I'm not infallible. Do this almost every day...
Or does anyone have any other idea what this could be???