Chevrolet 2009 Suburban Owner's Manual page 166

SBZA Detection Zones
The SBZA sensor covers a zone of approximately one
lane over from both sides of the vehicle, 11 ft. or
3.5 m. This zone starts at each side mirror and goes
back approximately 16 ft. (5.0 m). The height of the zone
is approximately between 1.5 ft. (0.5 m) and 6 ft. (2.0 m)
off the ground.
Use caution while changing lanes when towing a trailer,
as the SBZA detection zones do not change when a
trailer is towed.
2-60
How the System Works
Left Side Mirror Display
When the vehicle is started, both outside mirror displays
will briefly come on to indicate that the system is
operating. When the vehicle is moving forward, the left or
right side mirror SBZA display will light up if a vehicle is
detected in that blind zone. If the turn signal is activated
and a vehicle is also detected on the same side, the
SBZA display will flash to give you extra warning not to
change lanes.
SBZA displays do not come on while the vehicle is
approaching or passing other vehicles. At speeds
greater then 20 mph (32 km/h), SBZA displays may
come on when a vehicle you have passed remains in
or drops back into the detection zone.
Right Side Mirror
Display