GM Service Manual Online
For 1990-2009 cars only
    • Resynchronization may be necessary due to the security method used by the remote keyless entry system.
        The transmitter does not send the same signal twice to the receiver.
    • The receiver will not respond to a signal that has been sent previously.
        This prevents anyone from recording and playing back the signal from the transmitter.
    • Resynchronization may be necessary under the following conditions:
       - The battery in the transmitter is very weak.
       - The battery in the transmitter was replaced.
       - The battery in the vehicle has been in a low or no charge condition for an extended period of time.
    • In order to resynchronize the transmitter with the receiver, perform the following steps:
        1. Stand within 1.5 meters (5 ft) from the vehicle.
        2. Simultaneously press and hold the LOCK and UNLOCK buttons on the transmitter for 7 seconds.

The door locks should cycle in order to confirm synchronization.