2001 GMC Sonoma Owner's Manual - Page 84

To replace the battery 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 press and hold the LOCK and UNLOCK buttons on the transmitter at the same time for seven seconds. The door locks should cycle to confirm synchronization. If the locks do not cycle, see your dealer for service. 1. Insert a thin coin in the slot between the covers of the transmitter housing near the key ring hole. Remove the bottom by twisting the coin. 2. Remove and replace the battery with a three volt CR2032 or equivalent battery, positive (+) side up. 3. Align the covers and snap them together. 4. Resynchronize the transmitter. 5. Check the operation of the transmitter. 2-13