Cadillac 1999 DeVille Owner's Manual page 156

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 the Maintenance Schedule booklet. If
you see CHANGE ENGINE OIL, it means that you
have no oil life left and you should change your oil
right away.
2-96
The system should indicate changing the oil between
3,000 miles (5 000 km) and 7,500 miles (12 500 km).
It may indicate changing the oil before 3,000 miles
(5 000 km) depending on your driving habits. If the
vehicle has been driven 7,500 miles (12 500 km), it
will indicate to change the oil. If you drive in a dusty
area, you should change your oil every 3,000 miles
(5 000 km) or three months (whichever comes first)
unless the display indicates changing it sooner. 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.
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