ect LEXUS SC300 1991 Service Repair Manual

OKNG
OKNG
OKNG
INSPECTION PROCEDURE
1Check brake fluid level.
Check the amount of fluid in the bake reservoir.C
Check and repair brake fluid leakage and add fluid.
2Check brake fluid level warning switch.
See page BE±142.
Replace brake fluid level warning switch.
3Check for short in all the harness and components connected to brake fluid le\
vel warning light
(See page IN±33).
Repair or replace harness or connector.
Check and replace ABS & TRAC ECU.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±133
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DTC56, 57Pressure Sensor Circuit
CIRCUIT DESCRIPTION
The pressure sensor detects the TRAC accumulator hydraulic pressure and if \
it is low, it sends signals to the
ECU to operate the pump. If the pressure is high, it sends signals to th\
e ECU to stop the pump.
DTC No.DTC Detecting ConditionTrouble Area
56Pressure sensor terminal PR outputs below 1 V for
about 1 sec. or more.
Open or short in pressure sensor circuit.
57
TRAC (BRAKE) control is executed continuouslymore
than 255 times while pressure sensor ONsignal is not
output.

Pressure sensor
Fail safe function: If trouble occurs in the pressure sensor circuit, the ECU cuts off current to the TRAC
solenoid relay and prohibits TRAC control.
BR±134
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals PR and E2 of ABS & TRAC ECU connector.
C
OK
P
C
Notice
1. Remove ABS & TRAC ECU with connectors stillconnected.
2. Operate the engine for about 30 seconds at idle speed to raise the pressure of TRAC actuator to a
high level.
1. Stop the engine and then turn ignition switch ON.
2. Measure voltage between terminals PR and E2 of ABS & TRAC ECU connector.
Voltage: 4 ± 8 V
1. Drain the fluid out of the actuator to reduce the pres-
sure (See page BR±48).
2. Measure voltage between terminals PR and E2 of ABS & TRAC ECU connector.
Voltage: 10 ± 14 V
Add fluid to reservoir after the check.
Check and replace ABS & TRAC ECU.
2Check harness and connector between ABS & TRAC ECU and TRAC actuator (See page IN±33).
Repair or replace harness or connector.
Replace TRAC actuator.
BR±136±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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WIRING DIAGRAM
DTC61TRAC ECU Communication Circuit Malfunc-
tion.
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
61
Either of the following (1) or (2) continues for more than
8 sec.:
(1) Vehicle speed signal of 4 wheels is less than 1 km/h
(1 mph) when TRCO signal is input.
(2) THFA signal is 0V when TRCO signal is not input.

Open or short in THFA, TRCO circuit

ABS & TRAC ECU

TRAC ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±138±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKOK
OKNG
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INSPECTION PROCEDURE
1Check voltage between terminals THFA, TRCO of ABS & TRAC ECU and body ground.
C
OK
PRemove ABS & TRAC ECU with connectors still con-
nected.
Measure voltage between terminals THFA, TRCO of
ABS & TRAC ECU and body ground when ignition
switch is turned ON.
Voltage: 10 ± 14 V
Check and replace ABS & TRAC ECU.
2Check for open and short in harness and connector between ABS & TRAC ECU and TRAC ECU
(See page IN±33).
Repair or replace harness or connector.
3Check voltage of terminals THFA, TRCO of TRAC ECU.
C
OK
PDisconnect ABS & TRAC ECU connector.
Measure voltage between terminals THFA, TRCO of
TRAC ECU and body ground when ignition switch is
turned ON.
Voltage: 10 ± 14 V
Check and replace TRAC ECU.
Check and replace ABS & TRAC ECU.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±139
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DTC62TRAC Vehicle Speed Malfunction
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
62
Detection of any of conditions (1) through (3):At vehicle speed of 10 km/h (6 mph) or more, pulses
are not input for 5 sec.

ECU
HINT: When DTC Nos. 31±36 are recorded in memory, DTC No. 62 is not recorded.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±140±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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NGOK
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INSPECTION PROCEDURE
1Check operation of stop light.
Check that stop light lights up when brake pedal is depressed and turns off when brake pedal is re-
leased.C
Repair stop light circuit (See page BE±78).
2Check voltage between terminal STP of ABS (& TRAC) ECU and body ground\
.
C
OK
PRemove ABS (& TRAC) ECU with connectors still con-
nected.
Measure voltage between terminal STP of ABS (&
TRAC) ECU and body ground when brake pedal is de-
pressed.
Voltage: 8 ± 14 V
Proceed to next circuit inspection shown on problem
symptoms chart (See page BR±74).
3Check for open in harness and connector between ABS (& TRAC) ECU and s\
top light switch
(See page IN±33).
Repair or replace harness or connector.
Check and replace ABS (& TRAC) ECU.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±143
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WIRING DIAGRAM
ABS Warning Light Circuit
CIRCUIT DESCRIPTION
If the ECU detects trouble, it lights the ABS warning light while at the s\
ame time prohibiting ABS control.
At this time, the ECU records a diagnostic trouble code in memory.After removing the short pin of the DLC1,
connect a DLC1 or connect terminals Tc and E1 of the DLC2 to make the ABS warning light to blink and
output the diagnostic trouble code.DIAGNOSTIC CHARTPerform troubleshooting in accordance with the
chart below for each trouble symptom.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Perform troubleshooting in accordance with the chart below for each trouble sym\
ptom.
 


ABS warning light does not light up 


Go to step
 

ABS warning light remains on 

Go to step
BR±144±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKNG
INSPECTION PROCEDURE
1Check ABS warning light.
See Combination Meter Troubleshooting on page BE±159.
Replace bulb or combination meter assembly.
2Check ABS solenoid relay.
C
OK
P
OK
C
Remove solenoid relay from R/B No. 6.
Check continuity between each terminal of ABS sole-
noid relay shown below.
1. Apply battery voltage between terminals 4 and 6.
2. Check continuity between each terminal of ABS so-
lenoid relay shown below.
Replace ABS solenoid relay.
Repair or replace and check for open in harness and connector between ch\
eck connector and ABS
solenoid relay and body ground (See page IN±33).
BR±146±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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NOYES
YESNO
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INSPECTION PROCEDURE
3Is diagnosis trouble code output?
Perform diagnostic trouble code check on page BR±76.
Repair circuit indicated by the code output.
4Does ABS warning light go off if short pin is removed?
Check for short in harness and connector between warn-
ing light and data link connector 1 and ECU (See page
IN±33 ).
5Check ABS solenoid relay (See step No. ).
Replace ABS solenoid relay.
Repair or replace and check for short in harness
and connector between data link connector 1 and
ABS solenoid relay (See page IN±33).
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±147
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