Chevrolet 2003 Impala Owner's Manual page 76

Battery Replacement
Under normal use, the battery in your remote keyless
entry transmitter should last about three years.
You can tell the battery is weak if the transmitter won't
work at the normal range in any location. If you have
to get close to your vehicle before the transmitter works,
it's probably time to change the battery.
Notice: When replacing the battery, use care not to
touch any of the circuitry. Static from your body
transferred to these surfaces may damage the
transmitter.
To replace the battery do the following:
1. Insert a flat object like a coin into the slot on the
back of the transmitter. Gently pry apart the front
and back.
2. Gently pry the battery out of the transmitter. Do not
use a metal object.
3. Put the new battery into the transmitter as shown
on the transmitter. Use type CR2032 battery or
equivalent.
4. Put the two haives back together. Make sure the
halves are together tightly so water won't get in.
5. Resynchronize and then test the transmitter.
Resynchronization
After you have changed the battery in your transmitter.
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transmitter at the same time and hold for approximately
seven seconds or until one horn chirp is heard.
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do this, press the LOCK and UNLOCK buttons on the
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