1997 GMC Sonoma Owner's Manual - Page 56

To replace batteries in the Keyless Entry transmitter: Resynchronization Resynchronization 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 prevents 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 not more than five seconds,The door locks should cycle to confirm synchronization. If the locks do not cycle, see your dealer for service. 1. Insert a dime in the slot between the covers of the transmitter near the key ring hole. Remove the bottom by twisting the dime. 2. Remove and replace the battery with a Panasonic@-type battery (CR2032 or equivalent), positive side down. 3. Align the covers and snap them together. 4. Check the operation of the transmitter. 2-8