Horn
Press 
on the steering wheel pad to sound the horn.
See also:
Passenger Sensing System
The vehicle has a passenger sensing system for the front outboard passenger
position.
The passenger airbag status indicator will light on the overhead console
when the vehicle is started.
...
Underbody Maintenance
Use plain water to flush dirt and
debris from the vehicle's underbody.
Your dealer or an underbody car
washing system can do this. If not
removed, rust and corrosion can
develop. ...
Diagnostics
OnStar Vehicle Diagnostics will
perform a vehicle check every
month. It will check the engine,
transmission, antilock brakes, and
major vehicle systems. It also
checks the tire pressures, if ...