LEXUS SC400 1991 Service Repair Manual

DTC15, 16TRAC Solenoid Relay Circuit
CIRCUIT DESCRIPTION
This relay circuit supplies power to each traction actuator solenoid.When th\
e ignition switch is turned on, the
relay goes on.
DTC No.DTC Detecting ConditionTrouble Area
15
Conditions (1) through (3) continue for 0.2 sec.or more:
(1) TRAC solenoid relay (TSR) terminal voltage: Bat-
tery positive voltage
(2) All TRAC actuator solenoid: OFF(3) All TRAC ac-
tuator solenoid monitor voltage (in ECU): 0V

TRAC solenoid relay

Open or short in TRAC solenoid relay circuit

ECU
16
Conditions (1) through (3) continue for 0.2 sec.or more:
(1) TRAC solenoid relay (TSR) terminal voltage: 0V
(2) All TRAC actuator solenoid: OFF
(3) TRAC actuator solenoid monitor voltage (in ECU):
Battery positive voltage

TRAC solenoid relay

B+ short in TRAC solenoid relay circuit

ECU
Fail safe function: If tr ouble occurs in this relay circuit, the ECU cuts off the current to the ABS and TRAC
solenoid relays and prohibits ABS and TRAC control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±102±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±103
WhereEverybodyKnowsYourName

OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal 1 of R/B No. 6 (for TRAC solenoid relay) and\
body ground.
C
OK
PRemove TRAC solenoid relay from R/B No. 6.
Measure voltage between terminal 1 o R/B No. 6 (for
TRAC solenoid relay) and body ground.
Voltage: 10 ± 14 V
Repair or replace harness or connector.
2Check continuity between terminal 3 of R/B No. 6 (for TRAC solenoid relay) \
and terminals SAC,
SMC, SRC or ABS & TRAC ECU.
C
OK
Hint
Check continuity between terminal 3 of R/B No. 6 (for
TRAC solenoid relay) and terminals SAC, SMC, SRC of
ABS & TRAC ECU.
Continuity
Resistance of the TRAC actuator solenoid is 2
.
Repair or replace harness or TRAC actuator.
BR±104
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName

OKNG
OKNG
3Check TRAC solenoid relay.
C
OK
P
OK
C
Remove solenoid relay from R/B NO. 6.
Check continuity between each terminal of TRAC sole-
noid relay shown below.
1. Apply battery voltage between terminals 4 and 6.
2. Check continuity between terminals shown below.
Replace TRAC solenoid relay.
4Check for open and short in harness and connector between TRAC solenoid 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±105
WhereEverybodyKnowsYourName

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)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±107
WhereEverybodyKnowsYourName

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)
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±111
WhereEverybodyKnowsYourName