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