Lincoln MKS 2016 Owner's Manual page 175

Blocked Sensor
The surface of the radar in the grille is dirty or obstructed in some way.
The surface of the radar in the grille is clean but the message remains
in the display.
Heavy rain or snow is interfering with the radar signals.
Swirling water, or snow or ice on the surface of the road may interfere
with the radar signals.
You are in a desert or remote area with no other vehicles and no
roadside objects.
MKS (CLE) Canada/United States of America, enUSA, First Printing
Cruise Control
E145632
Cause
A message displays if something obstructs
the radar signals from the sensor. The sensor
is located behind a fascia cover near the
driver side of the lower grille. The system
cannot detect a vehicle ahead and will not
function when something obstructs the radar
signals. The following table lists possible
causes and actions for this message
displaying.
Clean the grille surface in front of the radar or remove the object
causing the obstruction.
Wait a short time. It may take several minutes for the radar to detect
that it is free from obstruction.
Do not use the system in these conditions because it may not detect
any vehicles ahead.
Do not use the system in these conditions because it may not detect
any vehicles ahead.
Wait a short time or switch to normal cruise control.
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Action