ABS LEXUS SC400 1991 Service Owners Manual

DIAGNOSTIC CHART
DIAGNOSTIC
CHART
WIRING DIAGRAM
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±119
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OKNG
OKNG
INSPECTION PROCEDURE
1Check speed sensor.
C
OK
P
OK
C
P
OK
C
OK
1. Remove front fender liner.
2. Disconnect speed sensor connector.
Measure resistance between terminals 1 and 2 of speed
sensor connector.
Resistance: 0.6 ± 1.8 k 
Measure resistance between terminals 1 and 2 of speed
sensor connector and body ground.
Resistance: 1 M or higher
1. Remove rear fender liner.
2. Disconnect speed sensor connector.
Measure resistance between terminals 1 and 2 of speed
sensor connector.
Resistance: 0.6 ± 1.7 k 
Measure resistance between terminals 1 and 2 of speed
sensor connector.
Resistance: 1 M or higher
Replace speed sensor.
2Check for open and short in harness and connector between each speed sensor a\
nd ECU (See
page IN±33).
Repair or replace harness or connector.
BR±120
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKNG
3Check sensor rotor and sensor installation.
C
OK
P
C
OK
C
OK
P
C
OK
Remove front speed sensor rotor (See page BR±71).
Check sensor rotor serrations.
No scratches or missing teeth.
Check the front speed sensor installation.
The installation bolt is tightened properly.
Remove the drive shaft (See page SA±64).
Check the sensor rotor serrations.
No scratches or missing teeth.
Check the rear speed sensor installation.
The installation bolt is tightened properly and there
is no clearance between the sensor and rear axle
carrier.
Replace speed sensor or rotor.
Check and replace ABS (& TRAC) ECU.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±121
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IN±33
WIRING DIAGRAM
DTC41IG Power Source Circuit
CIRCUIT DESCRIPTION
This is the power source for the ECU and becomes the power source for the CP\
U and actuators.
DTC No.DTC Detecting ConditionTrouble Area
41
Vehicle speed is 3 km/h (1.9 mph) or moreand voltage
of ECU terminal IG remains atmore than 17V or below
9.5V for more than 10 sec.
Battery

IC regulator

Open or short in power source circuit

ECU
Fail safe function: If trouble occurs in the power source circuit, the ECU cuts off current to the ABS
solenoid relay and prohibits ABS control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±122±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKNG
NGOK
INSPECTION PROCEDURE
1Check battery positive voltage.
Voltage: 10 ± 14 VOK
Check and repair the charging system.
2Check voltage between terminals IG1 and GND or ABS (& TRAC) ECU connec\
tor.
C
OK
PRemove ABS (& TRAC) ECU with connectors still con-
nected.
1. Turn ignition switch on.
2. Measure voltage between terminals IG1 and GNDof ABS (& TRAC) ECU connector.\
Voltage: 10 ± 14 V
Check and replace ABS (& TRAC) ECU.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±123
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OKNG
OKNG
3Check continuity between terminal GND of ABS (& TRAC) ECU connector and bod\
y ground.
C
OK
Measure resistance between terminals GND or ABS (&
TRAC) ECU connector and body ground.
Resistance: 1  or less
Repair or replace harness or connector.
4Check ECU±IG fuse.
C
OK
PRemove ECU±IG fuse from J/B No. 1.
Check continuity of ECU±IG fuse.
Continuity
Check for short in all the harness and components con-
nected to ECU±IG fuse (See attached wiring diagram).
Check for open in harness and connector between
ABS (& TRAC) ECU and battery (See page IN±33).
BR±124±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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WIRING DIAGRAM
DTC51ABS Pump Motor Lock
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
51Pump motor is not operating normally duringinitial
check.
ABS pump motor
Fail safe function: If trouble occurs in the ABS pump motor, the ECU cuts off the current to the solenoid
relay and prohibits ABS control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
See inspection of ABS pump motor (See page BR±65 or BR±68 ).
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±125
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IN±33
DTC53TRAC±Pump Motor Lock
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
53
TRAC pump motor is locked

Open for TRAC pump motor ground.

TRAC pump motor

Harness or connector between TRAC pump&
motor and body ground.

TRAC Actuator

ABS & TRAC ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±126±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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WIRING DIAGRAM
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±127
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OKNG
OKNG
INSPECTION PROCEDURES
1Check operation of TRAC pump & motor.
C
OK
P
Notice
Disconnect TRAC pump & motor connector.
Connect positive
lead to terminal 3 or TRAC pump &
motor connector and negative  lead to terminal 1.
Do not apply battery voltage for more than 3 sec.
The TRAC pump motor should emit an operating
sound.
Go to step 3.
2Check continuity between terminal 1 of TRAC pump & motor connector and b\
ody ground.
C
OK
Measure resistance between terminal 1 of TRAC pump
& motor connector and body ground.
Resistance: 0  (Continuity)
Repair or replace harness or connector.
Replace TRAC pump & motor.
BR±128±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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