Toyota Lexusc Owner's Handbook Manual page 203

OCCUPANT RESTRAINT SYSTEMS
CAUTION
D After inserting the tab, make sure the tab and buckle
are locked and that the lap and shoulder portions of
the belt and the seat belt extender are not twisted.
D Do not insert coins, clips, etc. in the buckle as this
may prevent you from properly latching the tab and
buckle.
D If the seat belt does not function normally,
immediately contact your Lexus dealer. Do not use
the seat until the seat belt is fixed, because it cannot
protect an adult occupant or your child from injury.
184
Seat belt pretensioners
The driver and front passenger's seat belt pretensioners
are designed to be activated in response to a severe
frontal impact.
When the sensor detects a severe frontal impact, the front seat
belts are quickly drawn back by the retractors so that the belts
snugly restrain the front seat occupants.