1991 LEXUS SC400 relay

DTC17, 18TRAC Motor Relay Circuit
CIRCUIT DESCRIPTION
This relay circuit supplies power to the TRAC pump motor. If the accumulator pressure drops, the ECU switches
the motor relay ON and operates the TRAC motor.
DTC No.DTC Detecting ConditionTrouble Area
17
Conditions (1) through (2) continue for 0.2 sec.or more:
(1) TRAC motor relay (TMR) terminal voltage: Battery positive voltage
(2) Voltage of ABS & TRAC ECU terminal MTT: 0 V

TRAC motor relay

Open or short in TRAC motor relay circuit

ECU
18
Conditions (1) and (2) continue for 2 sec. ormore:
(1) TRAC motor relay (TSR) terminalvoltage: 0 V
(2) Voltage of ABS & TRAC ECU terminal MTT: Battery positive voltage

TRAC motor relay

B+ short in TRAC motor relay circuit

ECU
Fail safe function: If trouble occurs in this relay circuit, the ECU cuts off the current to the TRAC solenoid
relay and prohibits TRAC control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±106±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal 1 of R/B No. 6 (for TRAC motor relay) and bo\
dy ground.
C
OK
PRemove TRAC motor relay from R/B No. 6.
Measure voltage between terminal 1 of
R/B No. 6 (for TRAC motor relay) and body ground.
Voltage: 10 ± 14 V
Check and repair harness or connector.
2Check continuity between terminal 2 of R/B No. 6 (for TRAC motor relay) and terminal MTT of
ABS & TRAC ECU.
C
OK
Hint
Check continuity between terminal 2 or R/B No. 6 (for
TRAC motor relay) and terminal MTT of ABS & TRAC
ECU.
Continuity
There is a resistance of 4 ± 6
between terminals BTM
and MTT of TRAC pump motor.
Repair or replace harness or TRAC pump motor.
BR±108
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKNG
OKNG
3Check TRAC motor relay.
C
OK
P
OK
C
Remove motor relay from R/B No. 6.
Check continuity between each pair of terminal of motor
relay shown below.
1. Apply battery voltage between terminals 3 and 4.
2. Check continuity between terminals shown below.
Replace TRAC motor relay.
4Check for open and short in harness and connector between TRAC motor relay and ABS &
TRAC ECU (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.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±109
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DTC21, 22,23, 24ABS Actuator Solenoid Circuit
CIRCUIT DESCRIPTION
This solenoid goes on when signals are received from the ECU and controls the\
pressure acting on the wheel
cylinders, thus controlling the braking force.
DTC No.DTC Detecting ConditionTrouble Area
21
Conditions (1) through (3) continue for0.05 sec. or more:
(1) ABS solenoid relay (SR) terminalvoltage: Battery positive
voltage
(2) Voltage of ABS (& TRAC) ECU terminal AST: Battery posi-
tive voltage
(3) When power transistor of ECU is ON,voltage of terminal
SFR is 0 V or batterypositive voltage.

ABS actuator

Open or short in SFR circuit.

ECU
22
Conditions (1) through (3) continue for0.05 sec. or more:
(1) ABS solenoid relay (SR) terminalvoltage: Battery positive
voltage
(2) Voltage of ABS (& TRAC) ECU terminal AST: Battery posi-
tive voltage
(3) When power transistor of ECU is ON,voltage of terminal
SFL is 0 V or batterypositive voltage.

ABS actuator

Open or short in SFL circuit.

ECU
23
Conditions (1) through (3) continue for0.05 sec. or more:
(1) ABS solenoid relay (SR) terminalvoltage: Battery positive
voltage
(2) Voltage of ABS (& TRAC) ECU terminal AST: Battery posi-
tive voltage
(3) When power transistor of ECU is ON,voltage of terminal
SRR is 0 V or batterypositive voltage.

ABS actuator

Open or short in SRR circuit

ECU
24
(Only ve-
hicles with TRAC)
Conditions (1) through (3) continue for0.05 sec. or more:
(1) ABS solenoid relay (SR) terminalvoltage: Battery positive
voltage
(2) Voltage of ABS & TRAC ECU terminal AST: Battery posi-
tive voltage
(3) When power transistor of ECU is ON,voltage of terminal
SRL is 0 V or batterypositive voltage.

ABS actuator

Open or short in SRL circuit.

ECU
Fail safe function: If trouble occurs in the actuator solenoid circuit, the ECU cuts off current to the
solenoid relay and prohibits ABS control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±110±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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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)
WhereEverybodyKnowsYourName

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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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)
WhereEverybodyKnowsYourName

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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