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 controlOn-vehicle inspection
1. INSPECT AIR-FUEL RATIO COMPENSATION SYSTEM
(a) Measure the voltage between the terminals of the ECM
connectors.
Standard:
NOTICE:
Connect test leads to the connector's backside. The connectors
should not be disconnected from the ECM.
HINT:
Voltage between the terminals of the EC ...