Pressing the button changes the vehicle-to-vehicle distance as follows:

The vehicle-to-vehicle distance is set automatically to long mode when the engine switch is turned to ignition on mode.
If a vehicle is running ahead of you, the preceding vehicle mark will also be displayed.
Vehicle-to-vehicle distance settings
Select a distance from the table below. Note that the distances shown correspond to a vehicle speed of 50 mph (80 km/h). Vehicle-to-vehicle distance increases/decreases in accordance with vehicle speed.

Adjusting the set speed
Canceling and resuming the speed controlSafety information for
children
Observe the following precautions when children are in the vehicle.
Use a child restraint system appropriate for the child, until the
child becomes large enough to properly wear the vehicle’s seat
belt.
It is recommended that children sit in the rear seats to avoid
accidental
contact ...