Low speed automatic cancellation

ACC is not functional at vehicle speeds below 18 mph (30 km/h). Once the vehicle speed drops below 18 mph (30 km/h), an audible alarm will sound, the head’s up display will flash and the automatic braking will be released.
See also:
Service Data Recording
Service data recorders in your vehicle are capable of collecting and
storing diagnostic information about your vehicle. This potentially
includes information about the performance or status of var ...
Vehicle storage
If you plan on storing your vehicle for an extended period of time
(30 days or more), refer to the following maintenance recommendations
to ensure your vehicle stays in good operating condition.
...
Under the Hood
Lincoln’s 5.4-liter V-8 engine develops 300 horsepower and 355 pounds-feet of
torque, and it mates with a four-speed-automatic transmission. The Navigator is
rated as an Ultra Low Emissions Vehicl ...
