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 settingsPerform zero point calibration of yaw rate and deceleration sensor (when
using intelligent tester)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Operate the intelligent tester to erase the codes
(select "RESET MEMORY").
HINT:
Refer to the intelligent tester operator's manual for
further details.
(d) Using the intell ...
Installation
1. INSTALL STEERING PAD
Support the steering pad with one hand as shown in
the illustration.
Connect the 2 connectors to the steering pad.
NOTICE:
When handling the airbag connector, take care
not to damage the airbag wire harness.
Connect the horn connector.
...
Reassembly
1. INSTALL COOLER DRYER
(a) Using needle nose pliers, install the cooler dryer.
(b) Install a new O-ring on the cap.
(c) Sufficiently apply compressor oil to the fitting
surfaces of the O-ring and the cap.
Compressor oil:
ND-OIL 8 or equivalent
(d) Using a hexagon wrench 14 mm ( ...