Horn
Press 
on the steering wheel pad to sound the horn.
See also:
Ignition Positions
The vehicle has an electronic keyless ignition with pushbutton start.
Pressing the button cycles it through three modes, ACC/ACCESSORY,
ON/RUN/START and STOPPING THE ENGINE/OFF.
If the push ...
Control Buttons
The buttons used to control the radio are:
RADIO/BAND: Press to turn the radio on and choose between AM, FM, and XM™,
if equipped.
MENU/SELECT: Press and turn to navigate the available menus.
...
OnStar Overview
If equipped, this vehicle has a
comprehensive, in-vehicle system
that can connect to a live Advisor
for Emergency, Security, Navigation,
Connection, and Diagnostic
Services.
The OnStar sy ...