Lexus SC 430 2004 Manual page 151

OCCUPANT RESTRAINT SYSTEMS
16sa52c
2. Fully extend the shoulder belt to put it in the lock mode.
When the belt is then retracted even slightly, it cannot be
extended.
To hold the infant seat securely, make sure the belt is in the lock
mode before letting the belt retract.
132
16sa53c
3. While pressing the infant seat firmly against the seat
cushion and seatback, let the shoulder belt retract as far as it
will go to hold the infant seat securely.