Cadillac 2011 STS Owner's Manual page 371

Reset the system whenever the engine oil is changed
so that the system can calculate the next engine oil
change. To reset the system:
1. Press the up or down arrow to scroll the DIC to
show OIL LIFE.
2. Once the XXX% ENGINE OIL LIFE menu item is
highlighted, press and hold the RESET button until
the percentage shows 100%.
If the percentage does not return to 100% or if the
CHANGE ENGINE OIL SOON message comes back on
when the vehicle is started, the engine oil life system
has not been reset. Repeat the procedure.
The engine air cleaner/filter is in the engine
compartment on the driver's side of the vehicle, near
the front. See
for more information on locating the air
cleaner/filter.
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