ABS SUBARU LEGACY 1997 Service Repair Manual

4-4
LM13-1]
BRAKES
13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

1
.
FEATURE

*
This
ABS
5
.3i
type
incorporates
the
hydraulic
control
unit,
ABS
control
module,
valve
relay
and

motor
relay
in
one
unit
for
betterproductivity
and
lightweight
.

*
The
ABS
(Anti-lock
brake
system)
electrically
controls
brake
fluid
pressure
to
prevent
wheel

"lock"
during
braking
on
slippery
road
surfaces,
thereby
improving
directional/steering
stability
as

well
as
shortening
the
braking
distance
.

*
If
the
ABS
becomes
inoperative,
the
fail-safe
system
activates
to
ensure
it
acts
asa
conventional

brake
system
.
The
warning
light
also
comes
on
to
indicate
that
the
ABS
is
malfunctioning
.

"
The
front-and-rear
wheels
utilize
a
4-sensor,
4-channel
control
design
:
the
front
wheels
havean

independent
control
design*1
and
the
rear
wheels
have
a
select
low
control
design*2
.

*1
:
A
system
which
independently
controls
fluid
pressure
to
left
and
right
front
wheels
.

*2
:
A
system
which
provides
the
same
fluid
pressure
control
for
the
two
rear
wheels
if
either
wheel

starts
to"lock
."

10
ABS
control
moduleand
hydraulic
control
unit
(ABSCM&H/U)
Proportioning
valve
OO
Diagnosisconnector
OO
ABS
warning
light

OO
Data
link
connector
(for
SUBARU
select
monitor)
OO
Transmission
control
module
(only
AT
vehicle)
Tone
wheel

OO
ABS
sensor
09
Wheel
cylinder
O
G
sensor
(only
AWD
vehicle)
>>
Brake
switch
D
Master
cylinder

?15A

2

BRAKES
IM13-21
4-4
13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

2
.
FUNCTIONS
OF
SENSORS
AND
ACTUATORS

Name
Function

ABS
control
moduleand
hydraulic
ABSCM-
e
Calculates
and
determine
the
conditionsof
the
wheels
and
body
from
control
unit
(ABSCM&H/U)
section
the
wheel
speedsand
makes
a
proper
decision
suitable
for
the
current
situation
to
control
the
hydraulic
unit
.

In
the
ABS
operation
mode,
the
module
outputs
a
cooperative
control
signal
to
the
AT
control
module
.
(AT
vehicles
only)

Whenever
the
ignition
switch
is
placed
at
ON,
the
module
makes
a
self
diagnosis
.
When
anything
wrong
is
detected,
the
module
cuts
off
the
system
.

Communicates
with
the
Subaru
select
monitor
.

H/U-section
In
the
ABS
operation
mode,
the
H/U
changes
fluid
passages
to
control

the
fluid
pressure
of
the
wheel
cylinders
in
response
to
an
instruction
from
the
ABSCM
.

The
H/U
also
constitutes
thebrake
fluid
passage
from
the
master
cylin-
der
to
the
wheel
cylinders
together
with
pipings
.

Valve
relay-
Serves
asa
power
switch
for
the
solenoid
valve
and
motor
relay
coil
in
section
response
to
an
instruction
from
the
ABSCM
.

Motor
relay-
Serves
as
a
power
switch
for
the
pump
motor
in
response
to
an
instruc-
section
tion
from
the
ABSCM
.

Wheel
speed
sensor
(ABS
sensor)
Detects
the
wheel
speed
in
terms
of
a
change
in
the
magnetic
flux
den-
sity
passingthrough
the
sensor,
converts
it
into
an
electrical
signal,
and
outputs
the
electrical
signal
to
the
ABSCM
.

Tone
wheel
Gives
a
change
in
the
magnetic
flux
density
by
the
teeth
around
the
tone
wheel
to
let
the
ABS
sensor
generate
an
electrical
signal
.

G
sensor
(AWD
vehicle
only)
Detects
a
change
in
G
in
the
longitudinal
direction
of
the
vehicle
and
outputs
it
to
the
ABSCM
in
terms
of
a
change
in
voltage
.

Stop
light
switch
Transmits
the
information
on
whether
the
brakepedal
is
depressed
or
not
to
the
ABSCM
for
use
as
a
condition
in
determining
ABS
operation
.

ABS
warning
light
Alerts
the
driver
to
an
ABS
fault
.
When
the
diagnosis
connector
and
diagnosis
terminal
are
connected,
the
light
flashes
to
indicate
a
trouble
codes
in
response
to
an
instruction
from
the
ABSCM
.

AT
control
module
(TCM)
(AT
vehicles
only)
Provides
shift
controls
(fixing
the
speed
at
3rd
or
changing
front
and
rear
wheel
transmission
characteristics
on
4WD
vehicle)
in
response
to
an
instruction
fromthe
ABSCM
.

4-4
[M13-21
BRAKES

13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

O

BATTERY

B4H1216A

O
ABS
control
module
and
S
Front
right
outlet
solenoidvalve
D
ABS
warning
light
hydraulic
control
unit
(2
Rear
left
inlet
solenoid
valve'
0
Stop
light
switch
9
ABS
control
module
section
D
Rear
left
outlet
solenoidvalve
0
Stop
light
Valve
relay
0
Rear
right
inlet
solenoidvalve
(5
G
sensor
(only
AWD
model)
O
Motor
relay
8
Rear
right
outlet
solenoid
valve
0
Front
left
ABS
sensor
m
Motor
R
Transmission
control
module
Z
Front
right
ABS
sensor
Front
left
inlet
solenoid
valve
(only
AT
module)
Z
Rear
left
ABS
sensor
8
Front
left
outlet
solenoidvalve
(3
Diagnosis
connector
(8
Rear
right
ABS
sensor
Front
right
inlet
solenoidvalve
0
Data
link
connector

BRAKES
[M13-4]
4-413
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

3
.
THEORY
OF
ABS
CONTROL

Refer
to
4-4
[M8-3]
.*1

4
.
ABSSENSOR

Refer
to
4-4
[M8-4]
.*1

4-4
[M13-51
BRAKES
13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

5
.
ABSCONTROLMODULEAND
HYDRAULIC
CONTROL
UNIT
(ABSCM&H/U)

*
ABS
CONTROL
MODULE
SECTION
(ABSCM)

The
ABSCM
is
a
digital
control
type
electronic
control
module
accommodating
two
microcontrol

modules
(MCMs)
;
master
and
slave
.
Both
MCMs
process
the
same
program
and
monitor
the

respective
outputs,
and
when
a
mismatch
occurs,
cut
off
the
system
to
activate
the
fail-safe
func-

tion
.

A
maximum
of
3
trouble
codes
are
stored
in
the
EEP
ROM
and
if
3or
more
areas
fail,
then
only
the

3
most
recent
failures
are
stored
.
The
trouble
codes
remain
stored
until
they
are
erased
.

This
ABSCM
inducesa
sequence
control
pattern
and
facilitates
the
checking
of
the
hydraulic
unit
.

"
ABS
control

Based
on
the
four
wheel
speed
signals,
the
ABSCM
calculates
a
simulated
body
speed
or
body

deceleration
rate,
whilereferencing
the
G
sensor
output
asan
auxiliary
means,
and
compares
them
with
the
wheel
speeds
and
wheel
deceleration
rates
.
If
it
determines
that
the
wheels
are

about
to
lock,
it
controls
the
solenoidvalve
or
motor
pump
of
the
H/U
to
adjustthe
brake
fluid
pres-

sures
that
act
on
the
wheel
cylinders,
thereby
preventing
the
wheels
from
locking
.

The
ABSCM
controls
the
right
and
left
front
wheel
fluid
pressures
independently
and
controls
the

rear
wheel
fluid
pressures
on
the
basis
of
the
wheel
which
is
more
likely
to
lock
(Select-low
control)
.

"
Select
monitor
associated
functions

The
Subaru
select
monitor
may
beused
to
perform
the
following
operations
.

O
To
read
out
analogdata
Toread
out
ON/OFF
data

O
Toread
out
or
erase
trouble
code

O
Toread
out
status
information
in
the
event
of
trouble
(Freeze
frame
data)

O
To
initiate
ABS
sequence
control
pattern

"
Indication
functions

The
ABS
warning
light
can
be
made
to
indicate
the
following
three
states
.

O
ABS
trouble

Flashes
to
indicate
trouble
codes
in
diagnosis
mode
.

O
Valve
ON/OFF
when
sequence
control
pattern
isin
effect

6

BRAKES
[M13-5]
4-413
.
Anti-lock
Brake
System
(AB
S)
[
5
.3i
Typ
e]

"
HYDRAULIC
CONTROL
UNIT
SECTION
(H/U)

The
H/U
is
a
fluid
pressure
controller
comprising
a
motor,
solenoid
valve,
housing,
relay,
etc
.
It

constitutes
two
diagonally
independent
brake
fluid
circuits
for
a
cross
piping
vehicle
.

"
The
pump
motor
rotates
an
eccentric
cam
to
let
the
plunger
pump
generatea
hydraulicpres-

sure
.

"
The
housing
accommodates
the
pump
motor,
solenoid
valve,
reservoir,
etc
.,
and
also
consti-
tutes
abrake
fluid
passage
.

"
The
plunger
pump
is
a
hydraulic
pump
which
drains
off
the
brake
fluid
which,
when
the
pressure

is
reduced,
is
discharged
to
the
reservoir,
and
sends
it
toward
the
master
cylinder
.

"
The
solenoid
valve
is
a
2-position
type
solenoidvalve
which
switches
the
brake
fluid
passages

between
the
wheel
and
master
cylinder
and
reservoir
sides
in
response
to
an
instruction
from
the

ABSCM
.

For
each
wheel
cylinder,
a
pairof
normally-closed
and
-opened
solenoid
valves
are
provided
.

*
The
inlet
solenoid
valve
is
duty-controlled
to
reduce
brake
fluid
pulsation
for
IowerABS
operation

noise
.

"
The
reservoir
is
a
fluid
chamber
which
temporarily
storesthe
brake
fluid
to
be
discharged
from

the
wheel
cylinder
when
the
pressure
is
reduced
.

"
The
damper
chamber
suppresses
thepulsation
of
the
brake
fluid
which,
when
the
pressure
is

reduced,
is
discharged
from
the
plunger
pump,
thereby
minimizing
the
kickbacks
to
the
brake

pedal
.

*
The
valve
relay
controls
the
solenoid
valve
and
motor
relay
energizing
power
supply
in
response

to
an
instruction
from
the
ABSCM
.
In
normal
(1G
ON)
condition,
the
relay
is
actuated
to
supply

power
to
the
solenoid
valve
and
motor
relay
.
When
an
error
occurs
in
the
system,
the
valve
relay

is
forced
to
OFF
to
keep
the
fluid
pressure
circuit
in
the
normal
mode
(normal
brake
mode)
and

also
constitute
the
ABS
warning
light
operating
circuit
.

"
The
motor
relay
supplies
power
to
the
pump
motor
to
operate
the
plunger
pump
in
response
to

an
instruction
from
the
ABSCM
in
the
ABS
control
mode
.

TheH/U
has
four
operating
modes
;
normal
mode
(control
OFF
:
normalbrake
mode),
"increase",

"hold"
and
"decrease"
modes
(control
ON
in
all
the
three
modes)
.

7

4-4
[M13-51
BRAKES
13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

1)
During
normal
braking(Explained
with
one
wheel's
control
asan
example)

Since
no
current
is
supplied
to
the
inlet
and
outlet
solenoid
valves,
no
solenoid
valve
attracting

force
is
generated
.
So
thevalves
remain
stationary
.

Accordingly,
the
inlet
port
of
the
inlet
solenoid
valve
isin
an
opened
state,
whereas
the
outlet
port

of
the
outlet
solenoidvalve
isin
a
closed
state
.
So
the
fluid
pressure
of
the
master
cylinder
is
trans-

mitted
to
the
wheel
cylinder
to
produce
abrake
force
in
the
wheel
cylinder
.

From
master
cylinder

v

N

Du

Reservoir

B4H0989

BRAKES
[M13-5]
4-413
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

2)
Pressure
"decrease"
action
with
ABS
in
operation(Explained
with
one
wheel's
control

as
anexample)

Current
is
supplied
to
the
inlet
and
outlet
solenoid
valves,
and
the
generated
solenoid
valve
attract-

ing
forces
close
the
inlet
port
and
open
the
outlet
port
.

Accordingly,
the
wheel
cylinder
is
isolated
from
the
master
cylinder
and
becomes
clear
to
the
res-

ervoir,
allowing
the
brake
fluid
to
flow
to
the
reservoir
.
So
the
fluid
pressure
of
the
wheel
cylinder

is
decreased
.

The
brake
fluid
collected
in
the
reservoir
is
fed
to
the
master
cylinder
by
the
pump
.

From
master
cylinder
\/
\/

Reservoir

B4H0990

9

4-4
IM13-5]
BRAKES
13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

3)
Pressure
"hold"
action
with
ABS
in
operation
(Explained
with
one
wheel's
control
asan

example)

Current
is
supplied
to
the
inlet
solenoid
valve,
and
the
generated
solenoid
valve
attracting
force

closes
the
inlet
port
.

Sinceno
current
is
supplied
to
the
outlet
solenoid
valve,
the
output
port
remains
in
a
closed
state
.

As
a
result,
the
wheel
cylinder,
master
cylinder
and
reservoir
are
blocked,
and
the
fluid
pressure

of
the
wheel
cylinder
is
maintained
constant
.

During
ABS
operation,the
pump
motor
continues
to
operate
.

From
master
cylinder
N~

O

Reservoir

B4H0991

10

BRAKES
[M13-5]
4-4
13
.
Anti-lock
Brake
System
(ABS)
[5
.3i
Type]

4)
Pressure
"increase"
action
with
ABS
in
operation(Explained
with
one
wheel's
control
as
anexample)

Since
no
current
is
supplied
to
the
inlet
and
outlet
solenoid
valves,
no
solenoidvalve
attracting

force
is
generated
.
So
the
valves
remain
stationary
.

Accordingly,
the
inlet
port
of
the
inlet
solenoid
valve
isin
an
opened
state,
whereas
the
outlet
port

of
the
outlet
solenoid
valve
is
in
a
closed
state
.
So
the
fluid
pressure
of
the
master
cylinder
is
trans-

mitted
to
the
wheel
cylinder
to
increase
the
brake
force
in
the
wheel
cylinder
.

During
ABS
operation,
the
pump
motor
continues
to
operate
.

From
master
cylinder
\
V

Reservoir

B4H0992

11