LEXUS SC400 1991 Service Repair Manual
Page 1121 of 4087
Check for Fluid Leakage.
BR±152±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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Page 1122 of 4087
TRACTION CONTROL SYSTEM (TRAC)
DESCRIPTION
BR0F3±01
The TRAC (Traction Control) system totally controls the engine torque and the braking of the driving wheels
(rear wheels). It helps avoid slippage of the driving wheels that tends to h\
appen during starting and accel-
eration and to maintain an optimal driving force according to the road surface conditions. The syst\
em elimi-
nates the need for a subtle accelerator pedal operation and improves veh\
icle stability when starting, accel-
erating or turning on slippery roads.
The TRAC system is an option.
SYSTEM PARTS LOCATION
BR0F4±01
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±153
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Page 1123 of 4087
HYDRAULIC SYSTEM DIAGRAM
BR0F5±01
BR±154±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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Page 1124 of 4087
WIRING DIAGRAM
BR0F6±01
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±155
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Page 1125 of 4087
ECU TERMINALS
ABS & TRAC ECU:
BR0F7±05
BR±156±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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Page 1126 of 4087
TRAC ECU:
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±157
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Page 1127 of 4087
ECU TERMINALS STANDARD VALUE
ABS & TRAC ECU:
BR0F8±03
Symbols
(Terminals No.) STD Voltage (V)\
\
Condition
BAT
(A25±21)
±
GND
(A25±22)
10±14
\
\
\
Always
IG
(A24±24)
±
GND
(A25±22)
10±14
\
\
\
IG switch ON
SR
(A24±22)
±
R±
(A24±25)
8.3±14
\
\
\
IG switch ON, ABS warning light OFF
MR
(A25±16)
±
R±
(A24±25)
Below 1.0\
\
\
IG switch ON
TSR
(A24±1)
±
R±
(A24±25)
8.3±14\
\
\
IG switch ON, TRAC indicator light OFF
TMR
(A24±9)
±
R±
(A24±25)
Below 1.0\
\
\
IG switch ON
SFR
(A25±1) ± GND
(A25±2) 10±14\
\
IG switch ON, ABS warning light OFF
SFL
(A24±13)
±
GND
(A25±22)
10±14
\
\
\
IG switch ON, ABS warning light OFF
SRR
(A24±26)
±
GND
(A25±22)
10±14
\
\
\
IG switch ON, ABS warning light OFF
SRL
(A25±12)
±
GND
(A25±13)
10±14
\
\
\
IG switch ON, ABS warning light OFF
AST
(A24±8)
±
GND
(A25±22)
10±14\
\
\
IG switch ON, ABS warning light OFF
SAC
(A24±12)
±
GND
(A25±22)
10±14\
\
\
IG switch ON, TRAC indicator light OFF
SMC
(A24±2) ± GND
(A25±22) 10±14\
\
IG switch ON, TRAC indicator light OFF
SRC
(A24±15)
±
GND
(A25±22
10±14
\
\
\
IG switch ON, TRAC indicator light OFF
PR
(A24±10)
±
E2
(A24±20)
5±7
\
\
\
IG switch ON
VC
(A24±19)
±
E2
(A24±20)
4±6
\
\
\
IG switch ON
ALT
±
GND Below 1.0\
\
IG switch ON
ALT
(A25±8) ± GND
(A25±22) 10±14\
\
Idling
WA
±
GND
Below 2.0\
\
IG switch ON, ABS warning light ON WA
(A25±9) ± GND
(A25±22) 10±14\
\
IG switch ON, ABS warning light OFF
PKB
±
GND
Below 1.5
\
\
\
IG switch ON, PKB switch ON,
Fluid in M/C reservoir above MIN level
PKB
(A25±17)
±
GND
(A25±22)
10±14
\
\
\
IG switch ON, PKB switch OFF,
Fluid in M/C reservoir above MIN level
BR±158±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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Page 1128 of 4087
Symbols
(Terminals No.)
STD Voltage (V)\
\
\
Condition
LBL
(A25±6) ± GND
(A25±22) 10±14\
\
IG switch ON
Fluid in M/C reservoir tank above MIN level.
STP
±
GND
Below 1.5\
\
\
Stop light switch OFF
STP
(A25±10)
±
GND
(A25±22)
8±14
\
\
\
Stop light switch ON
D/G
(A25±20) ± GND
(A25±22) 10±14\
\
IG switch ON, ABS warning light OFF
Tc
(A26±3)
±
GND
(A25±22)
10±14
\
\
\
IG switch ON
Ts
(A26±1)
±
GND
(A25±22)
10±14
\
\
\
IG switch ON
P
±
GND 10±14\
\
IG switch ON, Shift position in ªPº position P
(A26±10) ± GND
(A25±22) Below 1.5\
\
IG switch ON, Other shift position in ªPº position
N
±
GND
10±14\
\
\
IG switch ON, Shift position in ªNº position
N
(A26±5)
±
GND
(A25±22) Below 1.5\
\
IG switch ON, Other shift position in ªNº position
FR+
(A24±17) ±
FR±
(A24±4)
AC generation\
\
IG switch ON
Slowly turn right front wheel.
FL+
(A24±5)
±
FL±
(A24±18)
AC generation
\
\
\
IG switch ON
Slowly turn left front wheel.
RR+
(A25±14)
±
RR±
(A25±3)
AC generation
\
\
\
IG switch ON
Slowly turn right rear wheel.
RL+
(A25±4)
±
RL±
(A25±15)
AC generation
\
\
\
IG switch ON
Slowly turn left rear wheel.
FRO
(A26±15)
±
GND
(A25±22)
Pulse generation\
\
\
IG switch ON
Slowly turn right front wheel.
FLO
(A26±6)
±
GND
(A25±22)
Pulse generation\
\
\
IG switch ON
Slowly turn left front wheel.
RRO
(A26±13)
±
GND
(A25±22)
Pulse generation\
\
\
IG switch ON
Slowly turn right rear wheel.
RLO
(A26±4) ± GND
(A25±22) Pulse generation\
\
IG switch ON
Slowly turn left rear wheel.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±159
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Page 1129 of 4087
TRAC ECU:
Symbols
(Terminals No.)
STD Voltage (V)
\
\
\
Condition
BAT
(T13±8)
±
GND
(T14±14)
10±14
\
\
\
Always
BM
(T14±15)
±
GND
(T14±14)
10±14\
\
\
Always
IG
(T14±2)
±
GND
(T14±14)
10±14\
\
\
IG switch ON
ACM
(T14±13)
±
GND
(T14±14)
4±5\
\
\
IG switch ON
Sub throttle valve fully open
A
(T14±11) ± GND
(T14±14) 4±5\
\
IG switch ON
Sub throttle valve fully open
A
(T14±12)
±
GND
(T14±14)
4±5
\
\
\
IG switch ON
Sub throttle valve fully open
BCM
(T14±26)
±
GND
(T14±14)
4±5
\
\
\
IG switch ON
Sub throttle valve fully open
B
(T14±24)
±
GND
(T14±14)
4±5
\
\
\
IG switch ON
Sub throttle valve fully open
B
(T14±25)
±
GND
(T14±14)
4±5\
\
\
IG switch ON
Sub throttle valve fully open
TR5 ± E1 Below 1.0\
\
IG switch ON, Engine stopped
TR5
(T14±16) ±
E1
(T14±20) 10±14\
\
Engine idling
IDL1
±
E1 Below 1.0\
\
Engine idling, Main throttle valve fully closed
IDL1
(T14±10) ± E1
(T14±20) 10±14\
\
Engine idling, Main throttle valve fully open
IDL2
±
E1
Below 1.0\
\
IG switch ON, Sub±throttle valve fully closed
IDL2
(T14±22)
±
E1
(T14±20)
10±14\
\
\
IG switch ON, Sub±throttle valve fully open
VTH ± E1 Below 1.5\
\
IG switch ON, Main throttle valve fully closed
VTH
(T14±8)
±
E1
(T14±20) 3.0±5.5\
\
IG switch ON, Main throttle valve fully open
VSH ± E1 Below 1.5\
\
IG switch ON, Sub±throttle valve fully closed
VSH
(T14±19) ±
E1
(T14±20) 3.0±5.5\
\
IG switch ON, Sub±throttle valve fully open
TR2
(T14±21)
±
E1
(T14±20)
10±14\
\
\
IG switch ON
NEO
(T14±6)
±
E1
(T14±20)
Pulse generation\
\
\
Engine idling
CSW ± GND Below 1.5\
\
IG switch ON, TRAC cut switch pushed in
CSW
(T13±13) ±
GND
(T14±14) 10±14\
\
IG switch ON, TRAC cut switch released
Below 1 5
\
\
IG switch ON, PKB switch ON,
PKB
±
GND
(T14±14)
Below 1.5\
\
Fluid in M/C reservoir above MIN level
PKB
(T14±1) ± (T14±14)
10±14
\
\
IG switch ON, PKB switch OFF, 10±14\
\
Fluid M/C reservoir above MIN level
BR±160±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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Page 1130 of 4087
Symbols
(Terminals No.)
STD Voltage (V)\
\
\
Condition
IND
(T13±11) ± GND
(T14±14) 10±14\
\
IG switch ON, TRAC indicator light OFF
WT
±
GND
Below 2.0\
\
\
IG switch ON, TRAC OFF indicator light ON
WT
(T13±14)
±
GND
(T14±14)
10±14
\
\
\
IG switch ON, TRAC OFF indicator light OFF
STP ± GND Below 1.5\
\
Stop light switch OFF
STP
(T13±2) ±
GND
(T14±14) 8±14\
\
Stop light switch ON
P
±
GND 10±14\
\
IG switch ON, Shift position in ªPº position
P
(T13±7) ±
GND
(T14±14) Below 1.5\
\
IG switch ON, Other shift position in ªPº position
N
±
GND 10±14\
\
IG switch ON, Shift position in ªNº position
N
(T13±16) ± GND
(T14±14) Below 1.5\
\
IG switch ON, Other shift position in ªNº position
Tc
(T13±6)
±
GND
(T14±14)
10±14
\
\
\
IG switch ON
FRO
(T13±10)
±
GND
(T14±14)
Pulse generation
\
\
\
IG switch ON
Slowly turn right front wheel
FLO
(T13±3)
±
GND
(T14±14)
Pulse generation\
\
\
IG switch ON
Slowly turn left front wheel
RRO
(T13±12)
±
GND
(T14±14)
Pulse generation\
\
\
IG switch ON
Slowly turn right rear wheel
RLO
(T13±5)
±
GND
(T14±14)
Pulse generation\
\
\
IG switch ON
Slowly turn left rear wheel
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±161
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