1991 LEXUS SC400 brake

±MEMO±
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±117
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DTC
31, 32,
33, 34,35, 36
Speed Sensor Circuit
CIRCUIT DESCRIPTION
The speed sensor detects the wheel speed and sends the ap-
propriate signals to the ECU. These signals are used for control
of both the ABS and TRAC control systems. The front and rear
rotors each have 48 serrations. When the rotors rotate, the
magnetic field emitted by the permanent magnet in the speed
sensor generates an AC voltage. Since the frequency of this
AC voltage changes in proportion to the speed of the rotors
(wheels) the frequency is used by the ECU to detect the speed
of each wheel.
BR3583
BR3582
DTC No.DTC Detecting ConditionTrouble Area
31, 32,
33, 34
Detection of any of conditions (1) through (3):
(1) At vehicle speed of 10 km/h (6 mph) or more,
pulses are not input for 5 sec.
(2) Momentary interruption of the vehicle speed sen-
sor signal occurs at least 7 times in the time between
switching the ignition switch ON and switching it OFF.
(3) Abnormal fluctuation of speed sensor signals with
the vehicle speed 20 km/h (12 mph) or more.

Right front, left front, right rear and left rear
speed sensor.

Open or short in each speed sensor circuit.

ECU
35
Vehicle speed sensor signal is not input for about 1 sec.
while the left front and right rear with the vehicle speed
sensor signals are being checked IG switch ON.
Open in left front, right rear speed sensor cir-
cuit.

ECU
36
Vehicle speed sensor signal is not input for about 1 sec.
while the right front and left rear vehicle speed sensor
signals are being checked with the IG switch ON.
Open in right front, left rear speed sensor cir-
cuit.

ECU
HINT: DTC No. 31 is for the right front wheel speed sensor.
DTC No. 32 is for the left front wheel speed sensor.
DTC No. 33 is for the right rear wheel speed sensor.
DTC No. 34 is for the left rear wheel speed sensor.
Fail safe function: If trouble occurs in the speed sensor circuit, the ECU cuts off current to the ABS
solenoid relay and prohibits ABS control.
BR±118
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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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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