Mercedes-Benz A-Class Operator's Manual page 487

Warning/indicator lamp Possible causes/consequences and
or
exit the vehicle and keep a safe distance from it until the engine has cooled down
#
Check the coolant level (
#
Make sure that the air supply to the radiator is not obstructed.
#
Avoiding high loads on the engine, drive to the nearest qualified specialist workshop. In doing so, ensure that the
#
coolant temperature display remains below the red area.
M M Solutions
page 357).
→
Display messages and warning/indicator lamps 485