FORD 2013 F-550 v.2 - Manual (Page 231)

Hill descent control (if equipped)
Hill descent control allows the driver to set and maintain vehicle speed
while descending steep grades in various surface conditions.
WARNING: Hill descent control cannot control descent in all
surface conditions and circumstances, such as ice or extremely
steep grades. Hill descent control is a driver assist system and cannot
substitute for good judgment by the driver. Failure to do so may result
in loss of vehicle control, crash or serious injury.
Hill descent control can maintain vehicle speeds on downhill grades
between 2 mph (3 km/h) and 12 mph (20 km/h). Above 20 mph
(32 km/h), the system remains armed, but descent speed cannot be set
or maintained.
WARNING: Hill descent control does not provide hill hold at
zero mph (0 km/h). When stopped, the parking brake must be
applied and/or the vehicle must be placed in P (Park) or it may roll
away.
Hill descent control requires a cooling down interval after a period of
sustained use. The amount of time that the feature can remain active
before cooling varies with conditions. The system will provide a warning
in the message center and a chime will sound when the system is about
to disengage for cooling. At this time, manually apply the brakes as
needed to maintain descent speed.
230 Terrain Response
2013 F-250/350/450/550 (f23)
Owners Guide gf, 2nd Printing, December 2012
USA (fus)