Cadillac 1999 Eldorado Owner's Manual page 141

The Driver Information Center (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 engine oil right away.
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. See
"Engine Oil, When to Change" in the Index. 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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