Chevrolet 2008 Silverado 1500 Pickup Owner's Manual page 166

Read the instructions completely before attempting to
program the transmitter. Because of the steps involved,
it may be helpful to have another person assist with
programming the transmitter.
Be sure to keep the original remote control
transmitter for use in other vehicles, as well as,
for future programming. Only the original remote
control transmitter is needed for Fixed Code
programming. The programmed buttons should be
erased when the vehicle is sold or the lease ends.
See "Erasing Universal Home Remote Buttons"
later in this section.
Park the vehicle outside of the garage when
programming a garage door. Be sure that people
and objects are clear of the garage door or gate
that is being programmed.
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Programming Universal Home
Remote — Rolling Code
For questions or help programming the Universal
Home Remote System, call 1-866-572-2728 or go to
www.learcar2u.com.
Most garage door openers sold after 1996 are Rolling
Code units.
Programming a garage door opener involves
time-sensitive actions, so read the entire procedure
before starting. Otherwise, the device will time out
and the procedure will have to be repeated.
To program up to three devices:
1. From inside the vehicle, press the two outside
buttons at the same time for one to two seconds,
and immediately release them.