GMC 2004 Savana Van Owner's Manual page 93

To replace the battery in the keyless entry transmitter,
do the following:
1. Use an object like a coin to pry open the transmitter.
2. Once the transmitter is separated, use an object
like a pencil to remove the old battery. Do not use
a metal object.
3. Remove and replace the battery, positive (+)
side down.
4. Snap the transmitter back together tightly to be sure
no moisture can enter.
5. Press and hold the lock and unlock buttons on the
remote keyless entry transmitter for seven seconds
to resynchronize the transmitter.
6. Check the operation of the transmitter.
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