LEXUS SC400 1991 Service Repair Manual

OKNG
OKNG
INSPECTION PROCEDURE
1Check ABS actuator solenoid.
C
OK
Hint
Hint
OK
C
Check continuity between terminal 4 and 1, 3, 4, 6 of the ABS actuator connector.
Continuity
Resistance of each solenoid coil is 1.2
.
Check continuity between terminal 2 and 1, 4, 5, 6 of the ABS actuator connector.
Continuity
Resistance of each solenoid coil is 1.2
.
Replace ABS actuator.
2Check for open and short in harness and connector between ABS (& TRAC) ECU \
and actuator
(See page IN±33).
Repair or replace harness or connector.
If the same code is still output after the diagnostic trouble code is dele\
ted, check the contact condition
of each connection.
If the connections are normal, the ECU may be defective.
BR±112±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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±MEMO±
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±113
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DTC25, 26,27TRAC Actuator Solenoid Circuit
CIRCUIT DESCRIPTION
The TRAC actuator solenoid operates in accordance with signals from the ECU\
, changing TRAC to the normal,
pressure increase, pressure reduction or holding mode.
DTC No.DTC Detecting ConditionTrouble Area
25
Conditions (1) and (2) continue for 0.05 sec. ormore:
(1) TRAC solenoid relay (TSR) terminalvoltage: Bat-
tery positive voltage
(2) Voltage of ABS & TRAC ECU terminal SMC: 0 V
TRAC actuator

Open or short in SMC circuit

ECU
26
Conditions (1) and (2) continue for 0.05 sec. ormore:(1)
TRAC solenoid relay (TSR) terminalvoltage: Battery
positive voltage(2) Voltage of ABS & TRAC ECU termi-
nalSAC: 0V
TRAC actuator

Open or short in SAC circuit

ECU
27
Conditions (1) and (2) continue for 0.05 sec. ormore:(1)
TRAC solenoid relay (TSR) terminalvoltage: Battery
positive voltage(2) Voltage of ABS (& TRAC) ECU ter-
minal SRC: 0V
TRAC actuator

Open or short in SRC circuit

ECU
Fail safe function: If trouble occurs in this solenoid circuit, the ECU cuts off the current to the ABS and
TRAC solenoid relays and prohibits ABS and TRAC control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±114±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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WIRING DIAGRAM
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±115
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OKNG
OKNG
OKNG
INSPECTION PROCEDURE
1Check TRAC actuator solenoid.
C
OK
PDisconnect TRAC actuator connector.
Check continuity between each terminal of TRAC ac-
tuator shown below.
Replace TRAC actuator.
2Check for open and short in harness and connector between solenoid relay and E\
CU (See page
IN±33 ).
Repair or replace harness or connector.
3Check for short in harness and connector between SMC and SRC, SAC and SMC, an\
d SAC and
SRC terminals with TRAC actuator and ECU connectors are disconnected.
Repair or replace harness or connector.
If the same code is still output after the diagnostic trouble code is dele\
ted, check the contact condition
of each connection. If the connections are normal, the ECU may be defectiv\
e.
BR±116±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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±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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