BMW 325I 2001 Owners Manual

Overview
Controls and features
Operation, care
and maintenance
Owner service procedures
Technical data
Index Advanced technology
171n
IndexDataTechnologyRepairsCar careControlsOverview
Advanced technology:
Airbags172
Adaptive Transmission Control
(ATC)173
Automatic Stability Control plus
Traction ASC+T/Dynamic
Stability Control DSC173
Radio reception174
Four-wheel drive175
Safety belt tensioner175
Interior rearview mirror with
automatic dimmer176
Rain sensor177
Tire Pressure Control (RDC)178
Self-diagnostics179
Xenon lamps180
Technol-

172n
Deceleration sensors continuously
monitor the acceleration forces acting
upon the vehicle. If, as the result of
a frontal collision, a deceleration is
reached at which the protection of
the safety belts alone is no longer
adequate, the gas generators of the
driver and passenger-front airbags are
ignited. However, the passenger-side
airbag is only triggered if an additional
sensor has recognized that the
passenger seat is occupied.
In the event of a side collision, the Head
Protection and side airbags in the front
or rear
* are triggered if necessary.
390de319
The airbags located under the marked
covers inflate and unfold in a matter of
a few milliseconds. In this process, they
tear through the designed separation
points of the upholstered covers or
press them out.
Because the inflation process must be
virtually instantaneous, it is necessarily
accompanied by a certain amount of
ignition and inflation noise. The gas
required to inflate the airbags is not
dangerous, and the smoke associated
with it dissipates.
The entire process is completed within
fractions of a second.
Airbags

173n
IndexDataTechnologyRepairsCar careControlsOverview
On vehicles with an automatic trans-
mission, the Adaptive Transmission
Control (ATC) uses a number of factors
to calculate the gear which provides
maximum efficiency. In this process, it
considers your individual driving style
as well as current driving conditions.
ATC recognizes your personal driving
style from the positions and movements
of the accelerator pedal, deceleration
when braking, and lateral acceleration
through curves. Based on different shift
characteristics Ð from comfort-oriented
to performance-oriented Ð ATC will
select the appropriate gear.463us005
In order to include driving conditions in
its calculations, ATC registers curves
and both uphill and downhill gradients.
For example, if you maintain speed
through a curve, the transmission does
not shift up. On uphill gradients, it shifts
up only when the engine speed
increases in order to make more effi-
cient use of power reserves. On down-
hill gradients, ATC shifts down when
the speed of the vehicle increases and
the driver must apply the brakes.Highly sensitive sensors monitor the
number of revolutions of the wheels,
steering angle, lateral acceleration,
brake pressure and the movement of
the vehicle around its vertical axis.
If differences in the wheel speeds
occur, ASC+T recognizes the danger of
wheelspin and reduces torque. If
necessary, the system also responds
with additional brake applications at the
rear wheels.
In addition, DSC permanently monitors
the vehicle's current operating condition
and compares it with an ideal condition
that is calculated from the sensor's
signals. If deviations from this occur
(understeering or oversteering, for
instance), DSC can stabilize the vehicle
in fractions of a second by reducing
engine output and with the assistance of
braking intervention at individual
wheels. As a result, dangerous skids can
be prevented even as they are just
beginning.
You may need some time to become
accustomed to this system's interven-
tion. However, it provides optimum drive
force and vehicle stability.
The braking intervention may be
accompanied by sounds specific to the
system.
ATC
*
ASC+T/DSC
*

174n
Radio receptionThe 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
the other frequencies. However,
because FM transmissions rely on line-
of-sight broadcast waves, their effec-
tive reception range is limited. 360de084
The limitations inherent to radio recep-
tion in a moving vehicle have been
minimized by a number of innovative
system designs:
The Radio Data System (RDS) makes
sure that, for broadcast stations trans-
mitting on several frequencies, the
radio automatically tunes to the
frequency with the best reception
quality.
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.
The selection of the antenna takes place
within milliseconds, and is therefore not
noticed by the radio listener.

175n
IndexDataTechnologyRepairsCar careControlsOverview
Four-wheel drive Safety belt tensionerThe transmission of power to the four
drive wheels is provided permanently
through a transfer box. The distribution
of torque between the front and rear
axles is 38% to 62%.
Traditional differential locks at the front
and rear axles and in the transfer box
are not required. Their function is
assumed by automatic braking inter-
vention at all four wheels. These trac-
tion interventions are governed by
Automatic Differential Brake (ADB-X), a
sub-function of DSC.
If a wheel tends to slip, it is braked
automatically by ADB-X until it once
again gains traction, and drive force
can be transmitted to that wheel. In
addition, the drive force is distributed to
the remaining wheels during this 530us133
system intervention. Engine output is
also reduced if necessary.
When the DSC is deactivated, the
ADB-X traction intervention is set for
the maximum drive force. However, the
engine intervention and the stability
controls are no longer available. For
this reason, DSC should only be deacti-
vated in the exceptional circumstances
described on page 81.
The BMW 325xi is not an off-road
vehicle. Instead, permanent four-wheel
drive provides a high degree of vehicle
stability and tractive ability under all
road conditions, and will aid you in crit-
ical driving situations, e. g. driving in
extreme winter conditions or on loose
road surfaces.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
shoulder and lap belts within fractions
of a second. This reduces the tendency
to slide under the lap belt.
390de330

176n
Interior rearview mirror with automatic dimmer
*
The interior rearview mirror with auto-
matic dimming feature reduces blinding
from following traffic by adapting the
intensity of the reflected images to
correspond to levels of light registered
by the unit's sensors. The mirror reverts
to its undimmed setting as soon as the
light source disappears. One light
sensor is mounted on the front of the
mirror housing. This sensor, the one
that is directed forward, measures light
intensity in the area ahead of the
vehicle. The second sensor is inte-
grated within the mirror's glass. The
electronic control system compares the
light intensity from front and rear. The
difference provides the basic parameter
used to modulate an electrical current
and induce chemical changes in a
semisolid layer incorporated in the lens.463us013
The semisolid reacts chemically to
this electrical current, thus providing
dimming of the mirror through an infi-
nitely-variable range (electrochromic
technology).
As a result, it is no longer necessary to
dim the mirror manually, and the driver
can concentrate completely on traffic
conditions.

177n
IndexDataTechnologyRepairsCar careControlsOverview
Rain sensor
*
Depending on how wet the windshield
is, the rain sensor controls the opera-
tion 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 there is moisture on the glass, the
amount of light reflected is reduced
since the infrared light at the surface of
the windshield can escape. The quan-
tity of reflected light is thus a means of
gauging the degree of wetness on the
windshield.390de133
When the system is set to the "Intermit-
tent" wiper speed, the wipers react
immediately Ð if water is splashed onto
the windshield by vehicles traveling
ahead of you, for example. As a result,
the rain sensor contributes to driving
safety and comfort.

178n
Tire Pressure Control (RDC)
*
This system regularly checks tire pres-
sure and monitors all four tires even
while driving, so you do not have to.
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 transmitted
by a radio signal. If an irregularity is
detected, the transmission rate is
increased. 463de006
There is an antenna located right near
every wheel in the vehicle body. This
antenna picks up signals from its
respective wheel. A central electronics
system evaluates the quadruple signals
which it receives and forwards any
changes.
The RDC provides an important contri-
bution to driving safety.

179n
IndexDataTechnologyRepairsCar careControlsOverview
Self-diagnostics All of the important electrical and elec-
tronic systems in the vehicle are tested
regularly and automatically; the driver
does not have to perform any extra
operations or adjustments.
The indicator lamps also come on
briefly after the ignition has been turned
on.
While you are driving, the functional
status of the actuator motors (for the
windshield wipers, power windows,
seats, sliding/tilt sunroof, etc.) is
constantly analyzed by current
measurements in their relays.460de177
In the same manner, the electrical
resistance of the airbag ignition genera-
tors and all of the remaining airbag
components is measured at all times.
Any fault in this system would be
detected immediately by a current fluc-
tuation that would necessarily accom-
pany it. The fault would be indicated
immediately by the airbag warning
lamp.
Even after you shut off the engine, the
overall functional status of your vehicle
is monitored. For example, all of the
flaps of the heating and ventilation
system travel to the nearest limit posi-
tion. This action ensures that the
system will be able to provide
defrosting, regardless of other circum-
stances, e. g. if a malfunction in the air
conditioner/climate control system
should occur during the night while the
vehicle is parked.
A calibration cycle runs every tenth time
the engine is shut off. During this cycle,
the actuator motors move all air condi-
tioner/automatic climate control flaps to
their limit stops in both directions. The
limit positions and the return travel
paths are checked in this manner in
order to ensure that appropriate adjust-
ments for the operating elements can
be made at any time.You will hear the sounds of the air flaps
as the air conditioning system/auto-
matic climate control carry out their
self-diagnostic functions after the igni-
tion has been turned off. All of the other
self-diagnostics functions operate
silently in the background.
Any possible defects detected during
these self-diagnostics can be read out
by your BMW center and quickly
corrected during the vehicle's next
regularly scheduled maintenance.

180n
Xenon lamps
*
The xenon lamp provides forward illu-
mination with significantly more bright-
ness and uniformity than the traditional
halogen lamp.
In a xenon lamp, an electric arc replaces
the filament in order to generate 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,
there is a brief warm-up period.
Maximum brightness is attained in
approx. 15 seconds.390de134
Xenon lamps provide significantly
improved visibility, especially during
adverse weather and poor driving
conditions e. g. driving at night in heavy
rain or through road repair areas where
there are no lane markers.
Vehicles with xenon lamps are equipped
with an automatic headlamp range
control. Thus the highway is always
optimally lighted and drivers in
oncoming traffic are not blinded.
Xenon lamps make a significant contri-
bution to highway safety since other
highway users, bicyclists and motorcy-
clists in the right lane, and pedestrians
are more easily detected.