If you create an account on the GM owner's center on-line, it will let
you download a PDF of your owner's manual.

Transmitter Programming
Method 1-No Tools Required
In the event that a transmitter is lost, program the old and the new
transmitters into the memory of the remote control door lock receiver. Up to
4 transmitters may be programmed.

Important:

        .  Once entering this procedure, programming the first transmitter
erases all previous transmitters. You must program all transmitters.

        .  Program one vehicle at a time. One transmitter could be
programmed into other vehicles that are also on program mode in close
proximity.

 1.. Sit in the driver's seat.
 2.. Remove the ignition key from the ignition lock cylinder.
 3.. Close all vehicle doors.
 4.. Press and hold unlock on the door lock switch.
 5.. While holding the door lock switch in the unlock position, insert and
remove the ignition key twice. Do not rotate the ignition lock cylinder.
 6.. Insert the ignition key a third time leaving the key in the ignition
lock cylinder. The ignition must remain in the LOCK position for the rest of
the procedure.
 7.. Release the door lock switch. You will hear three chimes. This chime
feedback indicates that transmitter programming is active.
 8.. Press and hold the lock and unlock buttons at the same time on the
keyless entry transmitter for 12 seconds. You will hear two chimes. This
chime feedback indicates that the transmitter has been programmed
successfully.
 9.. Repeat step 8 for the rest of the transmitters (for a total of 4
transmitters).
 10.. Exit this procedure by removing the ignition key from the ignition
lock cylinder.

Locking Control Customization
Method 1-No Tool Required

Important
If the ignition switch is moved to the OFF position or any vehicle door is
opened during this procedure, the remote unlock verification customization
will be terminated and the system will remain in the most recent mode.

 1.. Sit in the vehicle driver's seat.
 2.. Close all the vehicle doors.
 3.. Turn the ignition switch to the RUN position.
 4.. Press and HOLD the door LOCK switch to the LOCK position.
 5.. Press the transmitter LOCK button. The chime will bong one to four
times, equal to the current customization mode, to indicate which mode the
vehicle is in. Each additional time the transmitter LOCK button is pressed,
the mode number will advance. A transition past mode four will repeat
starting again at mode one.
 6.. Release the door LOCK switch from the LOCK position when the desired
mode has been indicated by the chime.
 7.. Turn the ignition switch to the OFF position.
     Remote Lock Verification Customization

     Mode
    Remote Lock Verification

     1
    Disabled

     2
    Horn Only

     3
    Headlamps Only

     4
    Horn and Headlamps

I don't think you can program the "unlock" function....only the "lock"
function.

Hope this helps,

Ian