GMC 2010 Sierra 1500 Crew Cab Owner's Manual page 265

This gauge shows the engine coolant temperature.
It also provides an indicator of how hard the vehicle is
working. During a majority of the operation, the gauge
will read 210°F (100°C) or less. If the vehicle is pulling a
load or going up hills, it is normal for the temperature to
fluctuate and go over the 235°F (113°C) mark. However,
if the gauge reaches the 260°F (125°C) mark, it
indicates that the cooling system is working beyond its
capacity.
See
This indicates that one or more of the tires is
significantly underinflated.
A tire pressure message in the Driver Information
Center (DIC), can accompany the light. See
information. Stop and check the tires as soon as it is
safe to do so. If underinflated, inflate to the proper
pressure. See
for more information.
.
For vehicles with a tire
pressure monitoring
system, this light comes
on briefly when the engine
is started. It provides
information about tire
pressures and the Tire
Pressure Monitoring
System.
for more
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