Cadillac 2011 DTS Owner's Manual page 177

When the Adaptive Cruise Control radar is
blocked by snow, ice, or dirt, it may not detect a
vehicle ahead. Adaptive Cruise Control may not
have time to slow your vehicle enough to avoid a
collision. Do not use Adaptive Cruise Control
when the radar is blocked by snow, ice, or dirt.
Keep your radar clean. See Cleaning the
System later in this section.
ACC automatically slows your vehicle down when
approaching a slower moving vehicle. It then adjusts
your vehicle speed to follow the vehicle in front at the
selected follow distance. Your vehicle speed increases
or decreases to follow the vehicle in front of you, but will
not exceed the set speed. It may apply limited braking,
if necessary. When braking is active, your brake lights
will come on. Braking may feel or sound different than if
you were applying the brakes yourself. This is normal.
Adaptive Cruise Control may not detect and react
to stationary or slow moving vehicles or other
objects ahead of you. You could crash into
an object ahead of you. Do not use Adaptive
Cruise Control when approaching stationary or
slow moving vehicles or other objects.
Adaptive Cruise Control may not detect and react
to stationary or slow-moving vehicles or other
objects ahead of you. Your vehicle may accelerate
toward objects, such as a stopped vehicle that
suddenly appears after the lead vehicle changes
lanes. Your complete attention is always required
while driving and you should be ready to take
action and apply the brakes.
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