Ford 2015 F-150 Owner's Manual page 235

The radar sensor cover in the grille is dirty
or obstructed
The surface of the radar sensor cover is
clean but the message remains in the
display
Heavy rain, spray, snow or fog in the air
interferes with the radar signals
Swirling water, snow or ice on the road
surface interferes with the radar signals
System Limitations
WARNING
The collision warning system's brake
support only reduces collision speed
if you first apply your brakes. You
must brake as you would in any typical
braking situation.
Due to the nature of radar technology,
there may be certain instances where
vehicles do not provide a collision warning.
These include:
• Stationary vehicles or vehicles moving
below 6 mph (10 km/h).
• Pedestrians or objects in the roadway.
• Oncoming vehicles in the same lane.
• Severe weather conditions (see
blocked sensor section).
• Debris build-up on the grille near the
headlamps (see blocked sensor
section).
• Small distance to vehicle ahead.
• Large steering wheel and pedal
movements (very active driving style).
F-150 (TFC) Canada/United States of America, enUSA, Fourth Printing
Driving Aids
Cause
Clean the radar sensor cover or remove the
obstruction
Wait a short time. The radar may take
several minutes to reset after you remove
the obstruction
The collision warning system is temporarily
disabled. Shortly after weather conditions
improve, the collision warning system
automatically reactivates
The collision warning system is temporarily
disabled. Shortly after weather conditions
improve, the collision warning system
automatically reactivates
Damage to the front end of your vehicle
may alter the radar sensor's coverage area.
This may result in missed or false collision
warnings. Have an authorized dealer check
your radar sensor for proper coverage and
operation.
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Action