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 be also displayed.
Adjusting the set speed
Vehicle-to-vehicle distance settingsReassembly
1. INSTALL NO. 2 SEAT LEG SUB-ASSEMBLY
Install the No. 2 seat leg sub-assembly with the 3
bolts and 2 nuts.
Torque: 19 N*m (194 kgf*cm, 14 ft.*lbf)
NOTICE:
Tighten the bolts and nuts in the order shown in
the illustration.
Install the 3 clamps.
2. INSTALL NO. 2 SEA ...
Removal
1. REMOVE FRONT DOOR WINDOW FRAME MOULDING
Remove the screw.
Using a heat light, heat the front door window frame
moulding between 40 to 60 C (104 to 140 F).
NOTICE:
Do not heat the front door window frame
moulding excessively.
Slide the front door window frame moulding upward
...
Inspection
1. INSPECT FRONT SEAT INNER BELT ASSEMBLY RH
Release the seat belt (Buckle switch is ON).
Check the resistance between the terminals.
Standard
If the result is not as specified, replace the inner belt
assembly.
Inspect the buckle switch.
Fasten ...