GMC Cadillac CTS 2004 Owner's Manual page 218

You can select this feature by itself, or you can combine
it with Horn Sounds At Lock so that both the lights
flash and the horn chirps when you lock your vehicle.
The mode you selected is now set. You can either
exit the programming mode by following the instructions
later in this section or program the next feature
available on your vehicle.
Horn Sounds at Lock
This feature sounds the horn once when the remote
keyless entry transmitter is used to lock the vehicle.
All doors must be closed for this feature to work.
Programmable Modes
Mode 1: ON
Mode 2: OFF
Before your vehicle was shipped from the factory, it was
programmed to Mode 2. The mode to which the
vehicle was programmed may have been changed since
it left the factory. To program the vehicle to a different
mode, use one of the following procedures:
To change the mode using the Base audio system,
do the following:
1. Enter the personalization portion of the SETUP
menu following the instructions listed previously.
2. Scroll to HORN SOUNDS AT LOCK to highlight it.
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3. Press the TUNE/SEL knob to switch back and forth
between on and off.
When the mode is turned on, a check mark will
appear next to the feature name.
To change the mode using the Navigation system,
do the following:
1. Enter the Personalization menu following the
instructions listed previously.
2. Scroll to Remote Keyless Options to highlight it.
3. Press the TUNE/SEL knob to view the modes.
4. Scroll to Horn Sounds At Lock and press the knob
once to select it.
When the mode is turned on, an X will appear in
the box to the left.
If you select this feature to be on, Lights Flash At Lock
will also be on. You can choose Lights Flash At Lock
by itself, but Horn Sounds At Lock will always have
Lights Flash At Lock enabled when it is selected.
The mode you selected is now set. You can either exit
the programming mode by following the instructions
later in this section or program the next feature available
on your vehicle.