1998 GMC Safari Owner's Manual - Page 94

Sliding Door 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 has been sent previously. it This will prevent anyone from recording and playing back the signal from the transmitter. 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 latches in the open position. To close the sliding slide door, pull the handle toward the front to release the rear latch, and slide the door forward.