GMC 1997 Safari Owner's Manual page 84

Synchronization
Synchronization may be necessary due to the security
method used by this system. The transmitter does not
send the same signal twice to the receiver. The receiver
will not respond to a signal it has been sent previously.
This will prevent anyone from recording and playing
back the signal from the transmitter.
Sliding Door
To resynchronize your transmitter, stand close to your
vehicle and simultaneously press and hold the LOCK
and UNLOCK buttons on the transmitter for eight
seconds. The door locks should cycle to confirm
synchronization. If the locks do not cycle, see your
dealer for service.
To open the sliding side door, pull the handle toward the
back and slide the door to the rear until it rests in the
open detent position.
To close the sliding side door, you must first pull the
door past the open detent position.