wheel of a Diablo (and I assume later cars) has an internal sensor that
continuously tracks the air pressure in the tire. Should it drop below
about 28 PSI it will alarm the driver by switching on the "Tire Pressure
Indicator" light on the dash. The system is very useful. Lamborghini was
way ahead of its time in
such a system. What is even more remarkable is that the sensors
themselves do not need internal batteries. Instead they contain a magnet
and coil that generates enough current when the tire rotates to drive
The only problem is that if you get a flat and have to temporally fill
the tire with inflation foam the inflation rubber like "gunk"
inactivates the sensor. A simple procedure to remove the sensor and
clean it is provided here.
The tire must first be completely removed from the wheel rim. This is
required because when the sensor is reattached to the rim it must be
balanced (see below).
Figure 1. Wheel Air Pressure Sensor
The sensor is strapped around the central region of the wheel using a
gigantic hose clamp. Figure 2 shows one complete assembly on the
ground. Note the metal counter weight on the opposite side of the sensor
as it would sit on the wheel. If tire inflation foam was used to
keep a tire inflated the whole apparatus is very sticky and hard to work
with. The "hose clamp" is opened and slid through the sensor box.
The sensor box is then pried open with a screwdriver on the inside.
Figure 3 shows the electronic circuit board as it sits in the sensor box
before it is removed. It slides right up and out. Figures 4 and 5
show a circuit board removed. The large object mounted in the middle of
the board is the magnet and coil that once the wheel rotates generates
power to drive the single transistor and IC chip on the board. The
round circular coin shaped object is the actual pressure sensor drum
itself. How compressed it is what the electronics on the board reads.
Fortunately it is easy to clean this system up. Just run warm water
over the board and carefully wipe it clean. The sticky foam washes right
off. It may be necessary to use a probe to scrape between the IC
pins to get rid of all "gunk". See figure 6. The whole circuit
board should be free of any dirt and gunk before putting it back into
the plastic holder which also needs to be cleaned. Figure 7 shows
a clean circuit board.
The board within the plastic housing is the re-treaded with the "hose
clamp" and reattached to the wheel. The position of the metal
counter-weight should be such that the rim is completely balanced before
the tire is put back on. Check the system is working by driving
(slowly) with un-inflated tire for a mile or so. The indicator light on
the dash should come on. It can take a mile or so at slow speed for this
to happen. Then inflate the tire completely and recheck. It should no
longer be lit.