GMC Cadillac CTS 2004 Owner's Manual page 73

1. Use a flat thin object to pry open the transmitter.
2. Once the transmitter is separated, use a pencil
or similar object to remove the old battery. Do
not use a metal object.
3. Insert the new battery as the instructions under the
cover indicate.
4. Snap the transmitter back together tightly to be sure
no moisture can enter.
5. Press any button on the remote keyless entry
transmitter to resynchronize the transmitter.
6. Check the operation of the transmitter.
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