FORD 2009 F-550 v.1 - Manual (Page 290)

WARNING: This system is not designed to prevent contact with
small or moving objects. The system is designed to provide a
warning to assist the driver in detecting large stationary objects to
avoid damaging the vehicle. The system may not detect smaller
objects, particularly those close to the ground.
WARNING: Certain add-on devices such as large trailer hitches,
bike or surfboard racks and any device that may block the
normal detection zone of the RSS system may create false beeps.
The RSS detects obstacles up to
6 feet (2 meters) from the rear
bumper with a decreased coverage
area at the outer corners of the
bumper, (refer to the figures for
approximate zone coverage areas).
As you move closer to the obstacle,
the rate of the tone increases. When
the obstacle is less than 10 inches
(25.0 cm) away, the tone will sound
continuously. If the RSS detects a
stationary or receding object further
than 10 inches (25.0 cm) from the
side of the vehicle, the tone will
sound for only three seconds. Once
the system detects an object
approaching, the tone will sound
again.
The RSS may have reduced
performance or an increased chance
of false detection if the tailgate is
not locked and in the upright position. If the tailgate is down, the RSS
tone may be heard intermittently or continuously. The tone may also be
heard if items in the truck bed protrude rearward outside the bed.
2009 F-250/350/450/550 (f23)
Owners Guide, 1st Printing
USA (fus)
Driving
290