LEXUS SC400 1991 Service Repair Manual

BE±78).
BR±74 ).
IN±33 ).
WIRING DIAGRAM
Stop Light Switch Circuit
CIRCUIT DESCRIPTION
The stop light switch senses whether the brake pedal is depressed or releas\
ed, and sends a signal to the ECU.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±142±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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OKNG
NGOK
OKNG
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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±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±145
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OKNG
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
OKNG
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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IN±33).
WIRING DIAGRAM
Tc Terminal Circuit
CIRCUIT DESCRIPTION
Connecting between terminals Tc and E1 of the DLC1 or the DLC2 causes the ECU to display the diagnos-
tic trouble code by flashing the ABS warning light.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±148±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals Tc and E1 of DLC2 or DLC1.
C
OK
PTurn ignition switch ON.
Measure voltage between terminals Tc and E1 of DLC2
or DLC1.
Voltage: 10 ± 14 V
If ABS warning light does not blink even after Tc and E1
are connected,t he ECU may be defective.
2Check for open and short in harness and connector between ABS (& TRAC) ECU \
and DLC2 or
DLC1, DLC2 or DLC1 and body ground (See page IN±33).
Repair or replace harness or connector.
Check and replace ABS (& TRAC) ECU.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±149
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IN±33 ).
WIRING DIAGRAM
Ts Terminal Circuit
CIRCUIT DESCRIPTION
The sensor check circuit detects abnormalities in the speed sensor signal w\
hich can not be detected with
the diagnostic trouble code check.Connecting terminals Ts and E1 of the DLC1 in the engine compartment
starts the check.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±150±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal Ts and E1 of data link connector 1.
C
OK
PTurn ignition switch ON.
Measure voltage between terminals Ts and E1 of DLC1.
Voltage: 10 ± 14 V
If ABS warning light does not blink even after Ts and E1
are connected, the ECU may be defective.
2Check for open and short in harness and connector between ABS (& TRAC) ECU and D\
LC1,
DLC1 and body ground (See page IN±33).
Repair or replace harness or connector.
Check and replace ABS (& TRAC) ECU.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±151
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