Cadillac 2002 DeVille Owner's Manual page 196

Oil Life Indicator
This feature lets you know when to change the engine
oil. It's based on the engine oil temperatures and your
driving patterns.
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To see the display, press the INFO button several times until
ENGINE OIL LIFE appears. If you see 99% ENGINE OIL
LIFE, 99 percent of your current oil life remains.
The DIC may display a CHANGE ENGINE OIL
message. Always keep a written record of the mileage and
date when you changed your oil. For more information,
see "Maintenance Schedule" in the Index. If you see
CHANGE ENGINE OIL, it means the oil life is gone and
you should change the oil right away. The system doesn't
check how much oil you have, so you'll still have to check
for that. To see how, see "Engine Oil" in the Index.
When the oil is changed, you'll need to reset the system.
See "Oil Life Indicator, How to Reset" in the Index.