Lexus SC300 / Lexus SC400. Service manual — part 957
143
ABS (ANTI–LOCK BRAKE SYSTEM)
144
ABS (ANTI–LOCK BRAKE SYSTEM)
M
A
11
MR
A
4
R–
A
5
SR
A
6
SFL
A
12
SRR
A
8
AST
A
9
MT
B
1
SFR
B
16
PKB
B
2
GND
B
13
GND
B
1
B
4
B
3
B
2
B
5
A
4
A
3
A
1
2
1
IG1
19
IO1
5
IO1
7
EB
EA
16
22
23
11
EB1
6
IK1
10
IJ
EA
1
3
4
3
2
1
6
1
4
2
IK2
25
IK2
2
IE1
1
IE2
12
2
1
E10
I23
I25
E 9
2
6
6
6
6
6
6
6
6
6
6
B
10
WA
B
6
TS
5
6
E12
L
P–B
V–Y
L–W
L–W
L
W
V–
Y
L
W–
B
L–
W
V–
Y
Y–
L
R
R
R
B–
R
B–
R
B–
R
P–
B
V
L
L
L
V
L
V–
Y
V
R–
Y
Y
B–
Y
P
L–
W
Y–
G
R–
W
R
–
W
W–
B
W–
B
R–
W
R–
W
B
B
W–
B
W–
B
W–
B
W–
B
W–
B
L–
W
L
W–
B
SFR
SFL
SRR
AST
MT
BS
BM
GND
WA
TS
TC
WB
BATTERY
ABS ECU (W/O TRACTION CONTROL)
R
12
0A
A
L
T
6
0
A
ABS
N
O
.
1
A
B
S
M
OT
OR
RE
L
A
Y
ABS
AC
T
U
AT
O
R
RE
L
A
Y
CHECK
CONNECTOR
FUSE BLOCK
R–W
DI
O
DE
(F
O
R
PA
R
KI
N
G
BR
AKE
)
BR
AKE
F
L
U
ID
L
EVEL
SW
PARKING
BRAKE
SW
ABS ACTUATOR
(CA
NA
DA
)
(US
A
)
B1
D2
A 4
, A 3 3
P 3
A22
, A 23
B
B
A
A
C 3
F 9
SHORT PIN
145
1
2
A
21
DG
B
17
TC
B
11
IG
B
22
BAT
B
7
STP
B
14
RL+
B
3
RL–
B
8
RSS
B
19
RR+
B
20
RR–
A
5
FL–
A
18
FL+
A
2
FSS
A
1
FR+
B
7
FR–
IO1
2
IO1
8
IE2
7
IO1
1
4
14
A
1
B
15
BW1
7
BW1
3
BW1
8
BW1
2
BW1
5
BW1
6
Bc2
6
Bc2
2
Bc2
5
I26
I26
2
3H
13
1E
12
1I
8
1I
10
3D
13
3A
4
3H
12
1H
1
1E
20
3E
3
2
1
2
1
1
2
1
2
L
P–B
P–B
(SHIELDED)
W
B
W–
B
O–
L
W–
L
W
O
W–
B
L–G
L–
Y
W
O
BR
–
B
O
L–
G
L–Y
W–
L
O–
L
B
W
P–
B
V–
W
B–
R
R
G–
W
G
–
W
G
–
W
W
Y
Y
R
B–
R
P–
B
P–
B
V–
W
TC
ABS
T 6
C13
, C1 4
S12
A22
, A 23
A 7
FROM POWER SOURCE SYSTEM (SEE PAGE 56)
10A
GAUGE
15A
ECU–IG
10A
DOME
15A
STOP
TDCL
ABS WARNING
LIGHT
[COMB. METER]
STOP LIGHT
SW
ABS ECU (W/O TRACTION CONTROL)
(SHIELDED)
FRONT LH
FRONT RH
REAR LH
REAR RH
ABS SPEED SENSOR
A31
A30
A 8
A
A
B
B
(SHIELDED)
2
1
I26
B17
B36
B34
W
I26
B17
BR
–
B
BR
–
B
BR
–
B
L–
G
L–Y
BR
BR
(SHIELDED)
(SHIELDED)
(SHIELDED)
(SHIELDED)
146
ABS (ANTI–LOCK BRAKE SYSTEM)
THIS SYSTEM CONTROLS THE RESPECTIVE BRAKE FLUID PRESSURES ACTING ON THE DISC BRAKE CYLINDERS OF THE RIGHT
FRONT WHEEL, LEFT FRONT WHEEL AND REAR WHEELS WHEN THE BRAKES ARE APPLIED IN A PANIC STOP SO THAT THE
WHEELS DO NOT LOCK. THIS RESULTS IN IMPROVED DIRECTIONAL STABILITY AND STEERABILITY DURING PANIC BRAKING.
1. INPUT SIGNALS
(1) SPEED SENSOR SIGNAL
THE SPEED OF THE WHEELS IS DETECTED AND INPUT TO TERMINALS FL+, FR+, RL+ AND RR+ OF THE ABS ECU.
(2) STOP LIGHT SW SIGNAL
A SIGNAL IS INPUT TO TERMINAL STP OF THE ABS ECU WHEN THE BRAKE PEDAL IS OPERATED.
(3) PARKING BRAKE SW SIGNAL
A SIGNAL IS INPUT TO TERMINAL PKB OF THE ABS ECU WHEN THE PARKING BRAKE IS OPERATED.
2. SYSTEM OPERATION
DURING SUDDEN BRAKING, THE ABS ECU WHICH HAS SIGNALS INPUT FROM EACH SENSOR CONTROLS THE CURRENT FLOWING
TO THE SOLENOID INSIDE THE ACTUATOR AND LETS THE HYDRAULIC PRESSURE ACTING ON EACH WHEEL CYLINDER ESCAPE TO
THE RESERVOIR.
THE PUMP INSIDE THE ACTUATOR IS ALSO OPERATING AT THIS TIME AND IT RETURNS THE BRAKE FLUID FROM THE RESERVOIR
TO THE MASTER CYLINDER, THUS PREVENTING LOCKING OF THE VEHICLE WHEELS.
IF THE ECU JUDGES THAT THE HYDRAULIC PRESSURE ACTING ON THE WHEEL CYLINDER IS INSUFFICIENT, THE CURRENT
ACTING ON SOLENOID IS CONTROLLED AND THE HYDRAULIC PRESSURE IS INCREASED.
HOLDING OF THE HYDRAULIC PRESSURE IS ALSO CONTROLLED BY THE COMPUTER, BY THE SAME METHOD AS ABOVE. BY
REPEATED PRESSURE REDUCTION, HOLDING AND INCREASE ARE REPEATED TO MAINTAIN VEHICLE STABILITY AND TO IMPROVE
STEERABILITY DURING SUDDEN BRAKING.
A 4
(B),
A 33
(A) ABS ACTUATOR
(A)3, (A)4–GROUND : ALWAYS APPROX. 12 VOLTS
(A)1–GROUND : ALWAYS CONTINUITY
(B)4, (B)5, (B)6–GROUND : APPROX. 1.15
(IGNITION SW OFF)
(B)2–GROUND :APPROX. 5
(IGNITION SW OFF)
A 7, A 8, A30, A31
ABS SPEED SENSOR FRONT LH, RH, REAR LH, RH
1–2 : APPROX. 1.0K
Ω
(20
°
C, 68
°
F)
A22
(A)
, A23
(B) ABS ECU
(B) 11–GROUND : APPROX. 12 VOLTS WITH IGNITION SW ON
(B)2, (B)13–GROUND : ALWAYS CONTINUITY
(B)22–GROUND
: ALWAYS APPROX. 12 VOLTS
(B) 1, (A) 6, (A) 12–GROUND : APPROX. 12 VOLTS WITH IGNITION SW ON
(B) 16–GROUND : CONTINUITY WITH PARKING BRAKE LEVER PULLED UP
(B) 7–GROUND :
APPROX. 12 VOLTS WITH STOP LIGHT SW ON
P 3
PARKING BRAKE SW
1–GROUND : CLOSED WITH PARKING BRAKE LEVER PULLED UP
S12
STOP LIGHT SW
1–2 : CLOSED WITH BRAKE PEDAL DEPRESSED
SYSTEM OUTLINE
SERVICE HINTS
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