GMC Sierra 2005 Owner's Manual page 100

The following instructions tell you how to change the
automatic door unlock mode (automatic transmission
only). Choose one of the four programming options
listed above before entering the program mode.
To enter the program mode, do the following:
1. Begin with the ignition off. Then pull the turn
signal/multifunction lever toward you and hold
it there while you perform the next step.
2. Turn the key to RUN and LOCK twice. Then, with the
key in LOCK, release the turn signal/multifunction
lever. Once you do this, the doors will lock and
unlock, the horn will chirp twice, and a 30-second
timer will begin. You are now ready to program the
automatic door unlock feature.
3. Press the door unlock switch once. You will
hear one, two, three, or four chimes. The number
of chimes tells you which unlock mode is currently
selected. Continue to press the door unlock
switch until the number of chimes that you hear
matches the number of the mode that you want.
2-12
If you take longer than 30 seconds, the locks will
automatically lock and unlock and the horn
will chirp twice to indicate that you have left the
program mode. If this occurs, you can repeat
the procedure beginning with Step 1 to re-enter
the programming mode.
You can exit the program mode any time by turning
the ignition to RUN. The doors will automatically
lock and unlock and the horn will chirp twice to
indicate that you are leaving the program mode.
If the lock/unlock switches are not pressed while in
the programming mode, the current automatic settings
will not be modified.
See your dealer for more information.