Lexus 2003 SC430 Owner's Manual page 127

COMFORT ADJUSTMENT
Front seat belt pretensioners
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The driver and front passenger's seat belt pretensioners
are designed to be activated in response to a severe
frontal impact.
When the airbag sensor detects the shock of a severe frontal
impact, the front seat belts are quickly drawn back by the
retractor so that the belts snugly restrain the front seat
occupants.
The front passenger seat belt pretensioner will not activate if
there is no passenger sitting in the front passenger seat.
However, the front passenger seat belt pretensioner may
activate if luggage is put in the seat, or the seat belt is buckled
up regardless of the presence of the occupant in the seat.
The seat belt pretensioners and SRS airbags may not operate
together in case of collisions at certain speeds and angles.
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This indicator comes on when the ignition switch is turned
to the "ON" position. It goes off after about 6 seconds.
This means the front seat belt pretensioners are operating
properly.
This warning light system monitors the airbag sensor
assembly, front airbag sensors, side airbag sensors, occupant
detection sensor, seat belt buckle switch, front seat belt
pretensioner assemblies, inflators, warning light,
interconnecting wiring and power sources. (For details, see
"Service reminder indicators and warning buzzers" on page
38.)