1991 LEXUS SC400 warning light

PROBLEM SYMPTOMS CHART
If a normal code is displayed during the diagnostic trouble code check but\
the problem still occurs, check
the circuits for each problem symptom in the order given in the table below\
and proceed to the page for
troubleshooting.
 Symptoms\
 \
Inspection Circuit See page
 


ABS does not oper-
ate.\
 
\

\

Only when 1.±4. are all normal and the problem is still occurring,
replace the ABS (& TRAC) ECU. 


BR±76
 


\
 
\

\

1. Check the diagnostic trouble code, reconfirming that the nor-
mal code is output. 

BR±122
BR±118
 \
 \
2. IG Power Source Circuit. BR±65 or 68 


\
 
\

\
3. Speed sensor circuit.
 


 




\
 
\


\

\

4. Check the ABS actuator with a checker.
If abnormal, check the hydraulic circuit for leakage (see page
BR±138). 




 


ABS does not oper-
ate efficiently.\
 
\

\

Only when 1.±4. are all normal and the problem is still occurring,
replace the ABS (& TRAC) ECU. 


BR±76
 


\
 
\

\

1. Check the diagnostic trouble code, reconfirming that the nor-
mal code is output. 


BR±118
BR±142
 \
 \
2. Speed sensor circuit. BR±65
or 68
 \
 \
3. Stop light switch circuit 
 




\
 
\


\

\

4. Check the ABS actuator with a checker.
If abnormal, check the hydraulic circuit for leakage (see page
BR±138). 




 


ABS warning light ab-
normal.\
 
\

\

1. ABS warning light circuit. 

BR±144
 \
 \
2. ABS (& TRAC) ECU. 
 




Diagnostic trouble
code check cannot
be performed.\
 
\


\

\

Only when 1. and 2. are all normal and the problem is still occur-
ring, replace the ABS (& TRAC) ECU. 




BR±144
 \
 \
1. ABS warning light circuit BR±148 


\
 
\

\
2. To terminal circuit.
 


 


Speed sensor signal
check cannot be per-
formed.\
 
\

\

1. Ts terminal circuit. 


BR±150
 


\
 
\

\
2. ABS (& TRAC) ECU.
 


BR±82±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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)
WhereEverybodyKnowsYourName

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)
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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)
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName