Toyota Lexusc Owner's Handbook Manual page 204

The front passenger's seat belt pretensioner will not activate
if no passenger is detected in the front passenger seat by the
front passenger occupant classification system. However, the
front passenger's seat belt pretensioner may activate if
luggage is put on the seat, or the seat belt is buckled up
regardless of the presence of an occupant in the seat. (As for
the front passenger occupant classification system, see page
219.)
The seat belt pretensioners and SRS airbags may not operate
together in case of collisions at a certain speeds and angles.
OCCUPANT RESTRAINT SYSTEMS
"
1 Front airbag sensors
2 Front seat belt pretensioner assemblies
3 SRS warning light
Airbag sensor assembly
4
5 Front passenger occupant classification system
(ECU and sensors)
6 Front passenger's seat belt buckle switch
185