See also:

Pre-collision seat belts (front seats of vehicles with pre-collision system)
If the pre-collision sensor detects that a collision is unavoidable, the pre- collision system will retract the seat belt, thus enhancing the effectiveness of the seat belt pretensioner in a crash ...

Have the vehicle inspected by your Lexus dealer immediately.
Failing to investigate the cause of the following warnings may lead to the system operating abnormally and possibly cause an accident. Have the vehicle inspected by your Lexus dealer immediately. ...

Operation and Maintenance
GENERAL INFORMATION You are responsible for ensuring that your Lexus is operated and maintained according to the instructions in the Owner’s Manual and the “Maintenance Information” section ...