GMC 2005 Sierra Denali Owner's Manual page 201

SRC (Source): Press this button to select a source:
radio, cassette tapes, CDs, or DVDs.
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SEEK : When listening to FM1, FM2, or AM,
press the up or the down arrow to go to the next or to the
previous station and stay there. This function is inactive if
the front seat passengers are listening to the radio.
When a cassette tape is playing, press the up or the
down arrow to go to the next or the previous selection.
This function is inactive if the front seat passengers are
listening to a cassette tape.
When a CD is playing, press the up arrow to go to the
next track on the CD. Press the down arrow to go to the
start of the current track if more than eight seconds have
played. This function is inactive if the front seat
passengers are listening to a CD.
PROG (Program): Press this button to go to the next
preset radio station set on the pushbuttons on the
main radio. This function is inactive if the front seat
passengers are listening to the radio.
When a cassette tape is playing, press this button to go to
the other side of the tape. This function is inactive if the
front seat passengers are listening to a cassette tape.
When a CD is playing, press this button to go to the
beginning of the CD. This function is inactive if the front
seat passengers are listening to a CD.
When a CD is playing in the six-disc CD changer, press
this button to select the next CD, if multiple CDs are
loaded. This function is inactive if the front seat
passengers are listening to a CD.
CD Changer
The CD changer plays up to six standard size CDs
continuously. Individual CDs may be loaded or ejected
into or from any position.
A green light on each numbered button indicates a CD
is loaded in the respective position. An amber light
on a numbered button indicates that a CD is playing.
When loading CDs, the loading slot indicators turn
amber to indicate that the player is ready to accept a
CD. CDs can be loaded or ejected with the radio or the
ignition off.
You must load CDs with the label side up. If you do not,
the player will automatically eject the CDs.
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