Cadillac 2007 STS Owner's Manual page 434

The tire pressure warning light may come on in
cool weather when the vehicle is first started, and
then turn off as you start to drive. This could
be an early indicator that the tire pressures are
getting low and need to be inflated to the
proper pressure.
Each tire, including the spare (if provided), should
be checked monthly when cold and inflated to
the inflation pressure recommended by the vehicle
manufacturer on the vehicle placard or tire
inflation pressure label. (If your vehicle has tires of
a different size than the size indicated on the
vehicle placard or tire inflation pressure label, you
should determine the proper tire inflation
pressure for those tires.)
434
Accordingly, when the low tire pressure telltale
illuminates, you should stop and check your tires
as soon as possible, and inflate them to the
proper pressure. Driving on a significantly
under-inflated tire causes the tire to overheat and
can lead to tire failure. Under-inflation also
reduces fuel efficiency and tire tread life, and may
affect the vehicle's handling and stopping ability.
As an added safety
feature, your vehicle has
been equipped with a
tire pressure monitoring
system (TPMS) that
illuminates a low tire
pressure telltale when
one or more of your tires
is significantly
under-inflated.