NOTE-
The
traction
control
system
referred
to
as
AST
(all
sea-
son
traction)
may
also
be
referred
to
as
ASC
(Automat-
ic
Stability
Control)
and
ASC+T
(Automatic
Stability
Control+Traction)
.
The
AST
system
improves
traction
by
electronically
apply-
ing
the
rear
brakes
when
therear
drive
wheels
are
spinning
at
a
faster
rate
than
the
front
wheels
.
The
combined
ABS/AST
control
module,
operating
through
the
ABS
hydraulic
control
unit,
modulates
braking
force
at
therear
wheels
.
In
addition,
AST
uses
retarded
ignition
timing
and
an
auxil-iary
engine
throttle
plate
to
reduceengine
torque
and
maintain
vehicle
stability
.
The
auxiliary
throttle
plate
is
held
open
by
spring
pressure
.
The
AST
system
actívates
the
auxiliary
throttie
position
motor
(ADS)
to
cose
the
AST
throttle
as
needed
.
This
reduces
the
volume
of
engine
intake
air
.
Due
to
the
throttle
closing
very
rapidly
during
AST
operationthe
driver
cannot
increase
theengine
power
output
regardless
of
how
far
theaccelerator
pedal
is
pushed
to
the
floor
.
The
auxiliary
throttle
plate
is
placed
ahead
of
the
conven-
tional
throttle
plate
in
the
throttle
body
.
Traction
control
also
comes
into
operationduringdecelera-
tion
.
Decelerating
on
snowy
or
icy
road
surfaces
can
lead
to
rear
wheel
slip
.
If
a
rear
wheel
startsto
drag
or
lock
up
when
the
throttle
is
closed
rapidly
orduringdownshifting,the
AST
system
can
limit
the
problem
by
advancing
the
ignition
timing
.
A
switch
on
the
center
console
is
used
to
togglethe
AST
on
or
off
.
The
AST
system
is
designed
to
be
maintenance
free
.
There
are
no
adjustments
that
can
be
made
.
Repair
and
trouble-
shooting
of
the
AST
system
requires
special
test
equipment
andknowledgeand
should
be
performed
only
by
an
autho-
rized
BMW
dealer
.
Table
a
lists
theconditions
indicated
by
the
AST
indicator
light
in
the
instrument
cluster
SUSPENSION,
STEERING
AND
BRAKES-GENERAL
300-5
Tablea
.
AST
Indicator
Lamp
Function
Indicator
lamp
1
Condition
1
Comment
Light
on
Normal
AST
start-
Automatic
AST
up
self-test
Light
off
AST
monitoring
Automatic
AST
op-
mode
eration
Press
AST
button,
AST
off
(disabled)
Rocking
the
car
tolight
comes
on
getout
of
snow
or
other
loose
surface
Driving
with
snow
chains
Press
AST
button
:
AST
monitoring
Automatic
AST
op-
light
goes
out
I
mode
eration
Light
flashes
AST
active
mode
I
Normal
AST
oper-
ation
as
it
controls
wheel
speed
Light
stays
on
af-
Defect
in
AST
Consult
BMW
ter
start
up
or
dealer
for
diagno-
comes
on
while
sis/repair
driving
(Vehicle
operation
remains
normal)
WARNING
-
Even
a
car
with
AST
is
subject
to
the
normal
physi-
cal
laws
.
Avoid
excessive
speeds
for
the
road
con-
ditions
encountered
.
CAUTION-
"
If
the
tires
on
the
carare
of
different
makes,
the
AST
system
may
over-react
.
Only
fit
tires
of
the
same
make
and
tread
pattem,
"In
adverse
conditions,
such
as
trying
to
rock
the
car
outof
deep
snow
or
another
soft
surface,
or
when
snow
chainsare
fitted,
it
is
advisable
to
switch
off
AST
and
allow
the
cars
driveline
to
op-
erate
conventionally
.
INTEGRATED
SYSTEMS
