What does the coolant temperature warning light mean?

The coolant temperature warning light (a thermometer symbol, sometimes shown with wavy lines) comes on when the engine is running hotter than it should, or occasionally when coolant level is low.

Overheating can warp or damage the engine if you keep driving on it, and that kind of repair is typically one of the more expensive ones a car can need.

The general advice is to pull over safely and switch the engine off as soon as it's practical to do so, rather than pushing on to your destination. Don't open the bonnet or coolant cap straight away - it can be extremely hot and pressurised.