Lexus 2003 SC430 Owner's Manual page 235

STARTING AND DRIVING
Tire pressure warning system
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This light and chimes warn you that the tire pressure is low.
This light comes on when the ignition switch is turned to the
"ON" position and goes off after a few seconds. This means
the low tire pressure warning light is operating properly.
If the warning light does not go off, or comes on or blinks during
driving, or the chimes sound, this indicates that air pressure is
low. Make sure there is no flat tire. If the warning light comes
on again even after air is put in the tires, a tire may be flat or
the system may be malfunctioning.
If this warning light comes on, the action you must take is
different depending on the type of tires used.
If you drive over about 180 km/h (112 mph) with the tires not
inflated at the designated pressure for high speed driving, the
warning light may turn on. If the tires are at the designated
pressure for ordinary speed driving, decreasing the speed will
turn off the warning light. (For the designated pressure for high
speed driving, see "Specifications" on page 318.)
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This warning light may turn on due to natural causes such as
natural air leaks or tire pressure changes caused by
temperature. In this case, adjusting the tire pressure will turn
off the warning light. For details about adjusting the tire
pressure, see "Checking tire pressure" on page 321.
Vehicles with run–flat tires:
If the warning light is on, the tire pressure is lower than
specified.
Stop your vehicle at a safe place as soon as possible and
check that the tire pressure is as specified on the tire pressure
label. The air pressure gauge is located in the tool bag. If the
warning light comes on or blinks even after tire pressure
adjustment, it is probable that you have a flat tire. If you cannot
verify the tire pressure soon, go to the nearest Lexus dealer or
authorized tire dealer at the moderate speed and do not ever
exceed 90 km/h (55 mph) and have all your vehicle's tires
checked and adjusted. And whether there is a flat tire or not
should be also checked at this time. If any tire must be
replaced, see "If you have a flat tire" on page 239.
If the warning light does not go off about more than 15 minutes
after air is put in the deflated tire, the system might be
malfunctioning. Consult your Lexus dealer.