1991 LEXUS SC400 Service Repair Manual

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Page 3833 of 4087

LEXUS SC400 1991 Service Repair Manual
135
B
4 RL+
B
15 RL±
B
5 RSS
B
14 RR+
B
3 ALT
BW1
3BW1 8
BW1
2
BW1
5
BW1
6
Bc2
6
Bc2
2 I26
12 12
W O W±B
L±G
L±Y
W
O
L±G L±Y
W
O
L±G L±Y
(
SHIELDED ) (
SHIELDED )
(
SHIELDED )
REAR LH REAR RH

Page 3834 of 4087

LEXUS SC400 1991 Service Repair Manual
136
ABS AND TRACTION CONTROL
I16E9
I14
I25 I25
I4
E13 I7
1E
12 1I 10 2 1I 8
14 8 17 4
IO1
8
IK2
9 3E
3
A1
B
15 B 5B1
B
22 GND1
B
2 GND2
B
13 GND3
B
6 LBL
B
17 PKB C
7 ABSO
C
12 BRP
C
8 BRC
C
7 THFA
C

Page 3835 of 4087

LEXUS SC400 1991 Service Repair Manual
137
B±RR
G±W
LG±R W
L±Y
B±Y
V±R
P±G P±L
LG±B LG
GR L
R±B
R±W TRACTION E CUE9 , E10
AB
I33
I36 I36 2
IK2
15 EB1 5
1B
5
3A6
B
11
IND B
14
WT B
8
BAT B
2
STP
A
16
TR5 A
2
IG A
15
BM A
21
TR2

Page 3836 of 4087

LEXUS SC400 1991 Service Repair Manual
138
ABS AND TRACTION CONTROL*1 : USA SPEC.
B
41 VC
B
43 VTA
B
64 IDL
B
46 THG
B
63 IDL2
B
44 THW
B
69 E1
A
26 BCM
A
25 B
A
24 B
A
11 A
A
12 A
A
13 ACM
A
14 GN D
A
20 E1
B
13 CSWA
10
IDL1 A
22
IDL2
1

Page 3837 of 4087

$LEXUS SC400 1991 Service Repair Manual 139 (FOR ABS) THIS SYSTEM CONTROLS THE RESPECTIVE BRAKE FLUID PRESSURES ACTING ON THE DISC\ BRAKE CYLINDERS OF THE RIGHT FRONT WHEEL, LEFT FRONT WHEEL AND REAR WHEELS WHEN THE BRAKES ARE APPLIED IN$

139
(FOR ABS)
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 DIRECTIONALLY STABILITY AND STEERABILITY DURING PANIC BRAKING.
1. INPUT SIGNALS
(1) SPEED SENSOR SIGNALTHE SPEED OF THE WHEELS IS DETECTED AND INPUT TO TERMINALS FL+, FR+, RL+ AND RR+ OF THE ABS AND TRACTION
ECU.
(2) STOP LIGHT SW SIGNAL A SIGNAL IS INPUT TO TERMINAL STP OF THE ABS AND TRACTION ECU WHEN THE BRAKE PEDAL IS OPERATED.
(3) PARKING BRAKE SW SIGNAL A SIGNAL IS INPUT TO TERMINAL PKB OF THE ABS AND TRACTION ECU WHEN THE PARKING BRAKE IS OPERATED.
2. SYSTEM OPERATION
DURING SUDDEN BRAKING, THE ABS AND TRACTION ECU WHICH HAS SIGNALS INPUT FROM E\
ACH 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, HOLD\
ING OF THE HYDRAULIC
PRESSURE IS ALSO CONTROLLED BY THE COMPUTER, BY THE SAME METHOD AS ABOVE. BY REP\
EATED PRESSURE REDUCTION,
HOLDING AND INCREASE ARE REPEATED TO MAINTAIN VEHICLE STABILITY AND TO IMPROVE STEERABILITY DURING SUDDEN
BRAKING.
(FOR TRACTION CONTROL)
THE TRACTION CONTROL SYSTEM IS A SYSTEM WHEREBY THE ªABS AND TRACTION ECUº AND ªTRACTION ECUº\
CONTROLS THE
ENGINE TORQUE AND THE HYDRAULIC PRESSURE OF THE WHEEL CYLINDER OF THE DRIVING WHEELS IN ORDER TO CONTROL
SPINNING OF THE DRIVING WHEELS WHEN STARTING OFF AND ACCELERATING, AND PROVIDE THE MOST APPROPRIATE DRIVING
FORCE IN RESPONSE TO THE ROAD CONDITIONS FOR VEHICLE STABILITY.
TRACTION CONTROL OPERATION
VEHICLE SPEED SIGNALS FROM THE SPEED SENSOR INSTALLED ON EACH WHEEL ARE INPUT TO THE ABS AND TRACTION ECU.
WHEN THE ACCELERATOR PEDAL IS DEPRESSED WHILE DRIVING ON A SLIPPERY ROAD AND THE DRIVING WHEEL (REAR WHEEL)
SLIPS, IF THE ROTATION OF THE REAR WHEEL EXCEEDS THE ROTATION OF THE FRONT WHEELS FOR A SPECIFIED PERIOD, THE
ECU JUDGES THAT THE REAR WHEEL IS SLIPPING.
WHEN THIS OCCURS, CURRENT FLOWS FROM TRACTION ECU TO SUB THROTTLE ACTUATOR TO CLOSE THE SUB THROTTLE
VALVE. THE THROTTLE VALVE OPENING ANGLE SIGNAL IS OUTPUT FROM TERMINAL VTA OF SUB THROTTLE POSITION SENSOR
TO TERMINAL VTA2 OF ENGINE AND ECT ECU TO KEEP THE ENGINE RPM AT THE MOST SUITABLE LEVEL FOR THE DRIVING
CONDITIONS AND REDUCE SLIP OF THE DRIVING WHEEL. AT THE SAME TIME, OPERATION OF THE ABS AND TRACTION ECU
CAUSE THE TRACTION BRAKE ACTUATORS (ACC CUT, M/C CUT, RESERVOIR CUT SOLENOID) TO TURN ON TO SWITCH THE
HYDRAULIC CIRCUIT TO ªTRACTIONº MODE.
IN THIS CASE, SIGNALS ARE INPUT FROM TERMINAL SRR OF ABS AND TRACTION ECU TO TERMINAL (B)6 OF ABS ACTUATOR, AND
FROM TERMINAL SRL OF ABS AND TRACTION ECU TO TERMINAL (B)1 OF ABS ACTUATOR, CONTROLLING THE REAR WHEEL
SOLENOID IN THE ABS ACTUATOR AND INCREASING THE HYDRAULIC PRESSURE OF THE WHEEL CYLINDER IN ORDER \
TO
PREVENT SLIP.
TO MAINTAIN THE HYDRAULIC PRESSURE OF THE REAR WHEELS, THE REAR WHEEL SOLENOID I\
NSIDE THE ABS ACTUATOR IS
PUT IN ªHOLDº MODE AND KEEPS THE HYDRAULIC PRESSURE TO THE BRAKE CYLINDER CONSTANT.
WHEN THE BRAKE CYLINDER HYDRAULIC PRESSURE IS REDUCED, THE PRESSURE REDU\
CTION MODE REDUCES AND CONTROLS
THE HYDRAULIC PRESSURE.
SYSTEM OUTLINE
WhereEverybodyKnowsYourName

Page 3838 of 4087

LEXUS SC400 1991 Service Repair Manual
140
ABS AND TRACTION CONTROL
A24(A), A25(B), A26(C) ABS AND TRACTION ECU
(B) 21±GROUND : ALWAYS APPROX. 12 VOLTS
(B) 11±GROUND : APPROX. 12 VOLTS WITH IGNITION SW AT ON POSITION
(B) 10±GROUND

Page 3839 of 4087

LEXUS SC400 1991 Service Repair Manual
141
: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR
CODESEE PAGEJUNCTION BLOCK AND WIRE HARNESS (CONNECTOR LOCATION)1B20ENGINE ROOM MAIN WIRE1E20INSTRUMENT PANEL WIRE1H1I20COWL WIRE1J20COWL WIRE
3A3B3D22

Page 3840 of 4087

LEXUS SC400 1991 Service Repair Manual
142
ABS AND TRACTION CONTROL
WhereEverybodyKnowsYourName

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