Cadillac 2004 DeVille Owner's Manual page 228

Once you have loaded the CDs in the magazine, slide
open the door of the CD changer. Push the magazine
into the changer in the direction of the arrow marked on
top of the magazine.
3-102
Close the door by sliding it all the way to the right. When
the door is closed, the changer will begin checking for
CDs in the magazine. This will continue for up to one and
a half minutes, depending on the number of CDs loaded.
Whenever a CD magazine with CDs is loaded in the
changer, the CD changer symbol will appear on the radio
display. If the CD changer is checking the magazine for
CDs, the CD symbol will flash on the display until the
changer is ready to play. When a CD begins playing, a
CD and track number will appear on the display. The CD
numbers are listed on the front of the magazine.
The features of the CD changer may be different due to
your vehicles audio system.