GMC 2006 Sierra 1500 Pickup Owner's Manual page 101

To replace the battery in the keyless entry transmitter,
do the following:
1. Insert a thin object, such as a 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. See
"Resynchronization" following this information.
5. Check the operation of the 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 that 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 15 seconds. The
door locks should cycle to confirm synchronization. If the
locks do not cycle, see your dealer for service.
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