GMC 2009 Yukon XL Owner's Manual page 163

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
SBZA can be disabled through the Driver Information
Center (DIC). See Driver Information Center (DIC)
on page 3-51 for more information. If the SBZA
is disabled by the driver, the SBZA mirror displays will
not light up during normal driving.
When the System Does Not Seem To Work
Properly
Occasional missed alerts can occur under normal
circumstances and will increase in wet conditions. The
system does not need to be serviced due to an
occasional missed alert. The number of missed alerts
will increase with increased rainfall or road spray.
If the SBZA displays do not light up when the system is
on and vehicles are in the blind zone, the system
may need service. Take the vehicle to your
dealer/retailer.
SBZA is designed to ignore stationary objects; however,
the system may occasionally light up due to guard
rails, signs, trees, shrubs, and other stationary objects.
This is normal system operation, the vehicle does
not need service.
2-57