Ford 2015 Fusion Owner's Manual page 201

Driving Aids
Why is the feature not available (line markings are gray) when I can see the lane markings
on the road?
Driving at high speeds in curves
Previous feature activation happened within the last one second
Ambiguous lane markings (mainly in construction zones)
Rapid transition from light to dark or vice versa
Sudden offset in lane markings
ABS or AdvanceTrac activation
Camera blockage due to dirt, grime, fog, frost or water on the windshield
Driving too close to the vehicle in front of you
Transitioning between no lane markings to lane markings or vice versa
Standing water on the road
Faint lane markings (partial yellow lane markings on concrete roads)
Lane width too narrow or too wide
Camera not calibrated after a windshield replacement
Driving on tight roads or on uneven roads
Why does the vehicle not come back into the middle of the lane always, as expected, in
the Aid or Aid + Alert mode?
High cross winds
Large road crown
Rough roads, grooves, shoulder drop-offs
Heavy uneven loading of the vehicle or improper tire inflation pressure
If the tires have been exchanged (including snow tires), or the suspension has been
modified
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Fusion (CC7) Canada/United States of America, enUSA