GMC 2001 Sierra 1500 Pickup Owner's Manual page 217

(5): Press this pushbutton to turn Dolby NR on and off.
Dolby NR is active when a tape is inserted in the remote
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cassette. The double D symbol will appear on the display.
Dolby Noise Reduction is manufactured under a license
from Dolby Laboratories Licensing Corporation.
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Dolby and the double D symbol are trademarks of
Dolby Laboratories Licensing Corporation.
FWD (6): Press this button to rapidly advance the tape.
The tape will rapidly advance to the end of the cassette
reel or until you press FWD again. The radio plays the
last selected station during FWD.
PROG: Press this button on the remote player to go
from one side of the tape to the other.
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TAPE: Press the AM FM button to switch from the
player and the radio when a tape is playing. To return to
the tape player, press CD AUX. The lighted arrow will
appear next to the symbol and show the direction of play
when a tape is active.
EJECT: Press this button on the remote player to
remove the tape. EJECT can be used with either the
ignition or radio off. Also, you must press EJECT before
loading a cassette with the radio off to allow loading.
3-30
Theft-Deterrent Feature (If Equipped)
R
THEFTLOCK is designed to discourage theft of your
radio. It works by using a secret code to disable all radio
functions whenever battery power is removed.
The THEFTLOCK feature for the radio may be used or
ignored. If ignored, the system plays normally and the
radio is not protected by the feature. If THEFTLOCK
is activated, your radio will not operate if stolen.
When THEFTLOCK is activated, the radio will display
LOC to indicate a locked condition anytime battery
power has been interrupted. If your battery loses power
for any reason, you must unlock the radio with the secret
code before it will operate.
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Activating the Theft Deterrent Feature
The instructions which follow explain how to enter
your secret code to activate the THEFTLOCK system.
It is recommended that you read through all nine steps
before starting the procedure.
If you allow more than 15 seconds to elapse between
any steps, the radio automatically reverts to time and
you must start the procedure over at Step 4.