GMC 2001 Sierra 1500 Pickup Owner's Manual page 211

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AM FM: Press this button to switch from a tape
to the radio.
TAPE AUX: Press this button to return to the tape
player when playing the radio. The lighted arrow will
appear and show the direction of play when a tape is
in the active mode.
EJECT: Press this button to remove the tape.
The radio will now play. EJECT can be used with
either the ignition or radio off. To load a cassette tape
with the ignition or radio off, press EJECT before
loading the cassette.
CLN: If this message appears on the display, the cassette
tape player needs to be cleaned. It will still play tapes, but
you should clean it as soon as possible to prevent damage
to the tapes and player. See "Care of Your Cassette Tape
Player" in the Index. After you clean the player, press and
hold EJECT for five seconds to reset the CLN indicator.
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The radio will display
3-24
to show the indicator was reset.
CD Adapter Kits
It is possible to use a portable CD player adapter kit
with your cassette tape player after activating the bypass
feature on your tape player.
To activate the bypass feature, use the following steps:
1. Turn the ignition to RUN or ACCESSORY.
2. Turn the radio off.
3. Press and hold the TAPE AUX button for five
seconds. The tape symbol on the display will flash
for two seconds, indicating the feature is active.
4. Insert the adapter into the cassette slot. It will
power up the radio and begin playing.
This override routine will remain active until EJECT
is pressed.