2001 BMW 540I SEDAN Owners Manual

Index
Data
Technology
Repairs
Car care
Controls
Overview
209nRadio reception
The AM frequency bands (medium-
wave, long-wave and short-wave) make
it possible to receive stations from a
great distance, because the broadcast
signals travel not only along the ground
as surface waves, but also as atmo-
spheric waves that are reflected from
the ionosphere.
Frequency-modulation (FM) provides
substantially better sound quality than
AM. However, because FM transmis-
sions rely on line-of-sight broadcast
waves, their effective reception range is
limited.
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Although numerous factors combine
to impose inherent limitations on the
reception quality available from mobile
radios, specially designed systems can
be employed to minimize their effects:
The Diversity Antenna system employs
several FM antennas integrated within
the rear window to provide three sepa-
rate sources for receiving broadcast
waves. An integral processor automati-
cally selects the antenna with the best
FM reception quality at any given time.
Because the ongoing antenna selection
process is completed within milli-
seconds, it remains inaudible to the
radio listener.

210nBMW active seat*Safety belt tensioner
BMW seats are configured for your
orthopedic well-being. The active seat
is an engineering enhancement of
BMW's seats, designed to ensure less
fatigue during extended trips while
sitting with little movement. The seat is
no longer a passive element between
the road, the running gear and the pas-
senger. Instead, it creates minor and
imperceptible shifts in your weight by
an active change in the contour of the
seat surface. The basic seat position is
not changed as this occurs.
Fluid cushions are located below the
surface of the seat in the seat's
upholstery on the left and right.
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The fluid is circulated slowly back and
forth between the two cushions by
means of a pump. This causes a move-
ment of the spinal column which is
nearly unnoticeable, resulting in an im-
proved flow of blood to the vertebral
discs and the muscles in the area of the
spinal column. Vehicle occupants can
experience less muscle cramping, back
pain in the spine's lumbar region and
fatigue. The active seat thus provides a
significant contribution to your driving
comfort and safety.
The safety belt tensioner responds to
severe frontal collisions by tightening
the belts to ensure that occupants
remain firmly positioned in their seats.
A gas-pressure system retracts the
buckle assembly to tension the shoul-
der and lap belts within fractions of a
second. This reduces the tendency to
slide under the lap belt.
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Overview
211nDSP sound system*Mirrors with automatic dimmer*
The DSP professional premium sound
system features a special amplifier
combined with Digital Sound Process-
ing (DSP) and integrated speakers to
surround you with crisp, true-to-life
sound reproduction.
The speaker system's subwoofers,
woofers, midrange speakers and tweet-
ers furnish you with an impressively full-
bodied listening experience. The indi-
vidual components are oriented so as
to produce the aural sensation that you
would experience facing the stage in a
concert hall. The system also automati-
cally adjusts the bass and treble set-
tings to compensate for changes in vol-
ume and vehicle speed.
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The interior and exterior mirrors with
automatic dimming feature reduce the
glare from following traffic by adapting
the intensity of the reflected images to
correspond to levels of light registered
by the unit's sensors. The mirrors revert
to their undimmed setting as soon as
the light source disappears.
One sensor is mounted on the front
of the interior mirror housing and is
designed to monitor light levels in the
area immediately forward of the vehicle.
A second sensor is integrated within
the mirror's glass.
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The electronic control system operates
by comparing the respective levels of
luminous intensity in front of and behind
the car. The difference provides the
basic parameter used to modulate an
electrical current and induce chemical
changes in a semisolid layer incorpora-
ted in the lens.
The semisolid reacts chemically to this
electrical current, thus providing infi-
nitely-variable dimming of the mirror
(electrochromic technology).
As a result, it is no longer necessary
to dim the mirror manually, and the
driver can maintain full concentration
on traffic.

212nRain sensor*
Depending on the degree of wetness
on the windshield, the rain sensor
controls the operation of the windshield
wipers.
Infrared light is carried along the
surface of the windshield in an optical
conductor in such a manner that it is
reflected completely when the wind-
shield is dry. The quantity of reflected
light is measured.
If the window is covered with beads of
water, the amount of light that is
reflected is decreased since the infra-
red light at the surface of the wind-
shield can then escape. The quantity of
reflected light is thus a means of
gauging the degree of wetness on the
windshield.
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When the system is set to the "Intermit-
tent" wiper speed, the wipers react
immediately – if water is splashed onto
the windshield by vehicles traveling
ahead of you, for example. As a result,
the rain sensor provides a contribution
to driving safety and comfort.

Index
Data
Technology
Repairs
Car care
Controls
Overview
213nTire Pressure Control (RDC)*
The Tire Pressure Control system (RDC)
assumes the task of regular tire pres-
sure checks for you. The tire pressure is
monitored at all four wheels, even when
the vehicle is moving.
Behind the valve stem in every wheel,
there is an electronic chip which is
designed for severe-duty applications
and long service life. It contains a pres-
sure sensor, a transmitter and a battery.
The pressure is measured in extremely
short time intervals and then transmit-
ted by a radio signal. If an irregularity is
detected, the transmission rate is
increased.
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Near every wheel, there are antennas in
the body which receive the signals from
all four wheels. A central electronics
system evaluates the quadruple signals
and forwards any changes.
The RDC provides an important contri-
bution to driving safety.

214nIntegrated rear suspension Level control system*
The control arms on the patented inte-
grated aluminum rear axle assembly are
not mounted directly on the body. They
are mounted elastically on a chassis
sub-frame which is joined in turn with
elasticity to the vehicle body. The result-
ing double elastic suspension system
effectively absorbs the forces resulting
from bumps and road surface irregulari-
ties.
The compliance rates of the integrated
rear axle assembly's control arm mounts
have been precisely calibrated to help
provide supplementary adjustment in
the tracking angle of the rear wheels
(programmed self-steer effect). The ulti-
mate result is enhanced safety and con-
trol under all conditions.
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The illustration shows the rear axle of the
sedan. With the lightweight, compact
rear axle of the sport wagon, the shock
absorbers are positioned at an angle.
The level control system for the rear
axle maintains constant ground clear-
ance of your vehicle, even when carry-
ing a load.
To achieve this, the vehicle is equipped
with air struts at the rear axle instead of
conventional shock absorbers and steel
suspension springs. With the help of
two sensors, an electronic control unit
calculates the height of the body at all
times and, if it is required, it allows air
which is generated in a compressor to
flow into the air springs.
As a result of the pressure increase in
the air springs, the level control system
ensures not only constant ride height,
but also ride comfort which is indepen-
dent of the load the vehicle is carrying.
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Index
Data
Technology
Repairs
Car care
Controls
Overview
215nXenon lamps*
The xenon lamps light up the side and
front areas of the vehicle with signifi-
cantly more brightness and uniformity
then the traditional halogen lamps.
In a xenon lamp, an electric arc
replaces the filament in order to gener-
ate intense illumination. A gas mixture
in a quartz glass tube with metal vapor
is ignited by a high electric voltage. The
arc that is generated is then sustained
by a lower voltage.
When the lamp is turned on, a brief
period is needed for the full beam
strength to build up. Maximum bright-
ness is attained in approx. 15 seconds.
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Xenon lamps provide significantly
improved visibility, especially during
adverse weather conditions and driving
situations (driving at night in heavy rain
or through road repair areas where
there are no lane markers, for instance).
Vehicles with xenon lamps
are
equipped with automatic headlamp
range control. As a result, the highway
is always optimally lighted, regardless
of load conditions, and drivers in on-
coming traffic are not blinded.
Xenon lamps make a significant contri-
bution to highway safety since other
highway users, or bicyclists and motor-
cyclists in the right lane, and pedestri-
ans are more easily detected.

216n