Cadillac 2009 DTS Owner's Manual page 167

When following a vehicle and entering a curve, ACC
could lose track of the vehicle in your lane and accelerate
your vehicle. When this happens the Vehicle Ahead
symbol will not appear.
ACC may detect a vehicle that is not in your lane and
apply the brakes.
ACC may, occasionally, provide a driver alert and/or
braking that you consider unnecessary. It could respond
to signs, guardrails, and other stationary objects when
entering or exiting a curve. This is normal operation.
Your vehicle does not need service.
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