Cadillac 2010 DTS Owner's Manual page 220

This light also comes on briefly when the vehicle is
started.
If the light does not go out or comes on and stays on
while driving, there may be a problem with the cooling
system. Driving with engine coolant temperature light on
could cause the vehicle to overheat, see Overheated
Engine Protection Operating Mode on page 6 32. See
Engine Overheating on page 6 29 and DIC Warnings
and Messages on page 4 66 for more information.
4-54
The engine coolant
temperature warning light
comes on when the
engine is very hot.
It indicates when the engine has warmed up and if the
cooling system is operating properly. If the gauge
pointer moves into the shaded area, the engine coolant
is too hot and the engine coolant temperature warning
light comes on. See Engine Overheating on page 6 29
for more information.
This gauge shows
the engine coolant
temperature.