ECU LEXUS SC400 1991 Service Repair Manual

BR0EY±05
ECU TERMINALS STANDARD VALUE
w/o TRAC:
 


Symbols
(Terminals No.) 

STD Voltage (V)\
 
\

\
Condition
 


BAT
(A23±22) 
± 


GND
(A23±13) 


10±14\
 
\

\

Always
 IG
(A23±11) ± GND
(A23±2) 10±14\
 \
IG switch ON
 

SR
(A22±5) 

±
 

R±
(A22±4) 

8.3±14
\
 
\

\
IG switch ON, ABS warning light OFF
 

MR
(A22±11) 

±
 

R±
(A22±4) 

Below 1.0
\
 
\

\
IG switch ON
 


SFR
(A23±1) 

±
 


GND
(A23±2) 

10±14
\
 
\

\
IG switch ON, ABS warning light OFF
 


SFL
(A22±6) 
± 


GND
(A23±13) 

10±14\
 
\

\
IG switch ON, ABS warning light OFF
 


SRR
(A22±12) 
± 


GND
(A23±13) 

10±14\
 
\

\
IG switch ON, ABS warning light OFF
 AST
(A22±8) ± GND
(A23±13) 10±14\
 \
IG switch ON, ABS warning light OFF
 

WA
 

±
 

GND
 

Below 2.0
\
 
\

\
IG switch ON, ABS warning light ON
 
WA
(A23±10) 
±
 
GND
(A23±13) 10±14\
 \
IG switch ON, ABS warning light OFF
 PKB ± GND Below 1.5\
 \
IG switch ON, PKB switch ON
 
PKB
(A23±16) ± 
GND
(A23±13) 10±14\
 \
IG switch ON, PKB switch OFF
 STP 
±
 GND Below 1.5\
 \
Stop light switch OFF
 STP
(A23±7) ± GND
(A23±2) 8±14\
 \
Stop light switch ON
 

D/G
(A23±21) 

±
 

GND
(A23±13) 

10±14
\
 
\

\
IG switch ON, ABS warning light OFF
 


Tc
(A23±17) 

±
 


GND
(A23±13) 

10±14
\
 
\

\
IG switch ON
 


Ts
(A23±6) 
± 


GND
(A23±2) 

10±14\
 
\

\
IG switch ON
 


FR+
(A22±1) 
± 


FR±
(A22±7) 


AC generation\
 
\

\

IG switch ON
Slowly turn right front wheel
 FL+
(A22±3) ± FL±
(A22±10) AC generation\
 \
IG switch ON
Slowly turn left front wheel
 

RR+
(A23±19)
 

±
 

RR±
(A23±20)
 

AC generation
\
 
\

\
IG switch ON
Slowly turn right rear wheel
 

RL+
(A23±14) 

±
 

RL±
(A23±3) 

AC generation
\
 
\

\
IG switch ON
Slowly turn left rear wheel
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±59
WhereEverybodyKnowsYourName

TROUBLESHOOTING
How to proceed with troubleshooting
Perform troubleshooting in accordance with the procedure on the followin\
g pages.

CUSTOMER PROBLEM ANALYSIS
Using the customer problem analysis check sheet for reference, ask the c\
ustomer in as much detail as
possible about the problem.
CHECK AND CLEAR THE DIAGNOSTIC TROUBLE CODES (PRECHECK)
If the ABS warning light lights up, and the ABS does not operate, the ECU \
stores diagnostic trouble codes
corresponding to the problem in memory.
Before confirming the trouble, 1st check the diagnostic trouble codes for any \
malfunction codes stored in
memory. When there are malfunction codes, make a note of them, then clear them \
and proceed to ª  Prob-
lem Symptom Confirmationº.
 PROBLEM SYMPTOM CONFIRMATION,  SYMPTOM SIMULATION
Confirm the problem symptoms. If the problem does not reoccur, simulate the problem by initially checking
the circuits indicted by the diagnostic trouble code in step , using ªProblem simulation methodº.
 DIAGNOSTIC TROUBLE CODE CHECK
Check the diagnostic trouble codes. If a malfunction code is output, proceed \
to ª  Diagnostic Trouble
Code Chartº. If the normal code is output, proceed to ª  Problem Symptoms Chartº. Be sure to proceed
to ª  diagnostic Trouble Code Chartº after steps and  are completed.
If troubleshooting is attempted only by following the malfunction code sto\
red in the memory, errors could
be made in the diagnosis.
 DIAGNOSTIC TROUBLE CODE CHART
If a malfunction code is confirmed in the diagnostic trouble code check,\
proceed to the inspection proce-
dure indicated by the matrix chart for each diagnostic trouble code.
 PROBLEM SYMPTOMS CHART
If the normal code is confirmed in the diagnostic trouble code check, perf\
orm inspection in accordance with
the inspection order in the problem symptoms chart.
 CIRCUIT INSPECTION
Proceed with diagnosis of each circuit in accordance with the inspection\
order confirmed in  and .
Determine whether the cause of the problem is in the sensor, actuators, wire harness and connectors or
the ECU.
\b SENSOR CHECK
Use the ABS warning light to check if each of the signals from speed sensors are being input correctly to
the ECU. Instructions for this check are given in the circuit inspection.
[10] REPAIRS
After the cause of the problem is located, perform repairs by following the i\
nspection and replacement pro-
cedures in this manual.
[11] CONFIRMATION TEST After completing repairs, confirm not only that the malfunction is eliminated\
, but also conduct a test drive
to make sure the entire ABS system is operating correctly. (In vehicles with the TRAC system, also check
the TRAC system.)
BR±72
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName

ECU DATA MONITOR USING LEXUS HAND±HELD TESTER
1. Hook up the LEXUS hand±held tester to the DLC2.
2. Monitor the ECU data by following the prompts on the testerscreen.
HINT: LEXUS hand±held tester has a ªSnapshotº function
which records the monitored data.
Please refer to the LEXUS hand±held tester operator's
manual for further details.
DIAGNOSTIC TROUBLE CODE CLEARANCE
1. Using SST, connect terminals Tc and E1 of DLC2 or DLC1. SST 09843±18020
2. IG switch ON.
3. Clear the diagnostic trouble codes stored in ECU by depressing the brake pedal 8 or more times within 3 seconds.
4. Check that the warning light shows the normal code.
5. Remove the SST from the terminals of DLC2 or DLC1.
6. Connect the Short Pin to DLC1.
HINT: Cancellation can also be done by removing the DOME
fuse, but in this case, other memory systems will also be can-
celled out.
ECU TERMINAL VALUES MEASUREMENT USING LEXUS BREAK±OUT±BOX AND LEXUS HANDHELD TESTER
1. Hook up the LEXUS hand±held tester and LEXUS
break±out±box to the vehicle.
2. Read the ECU input/output values by following the prompts on the scan tool screen.
HINT: LEXUS hand±held tester has a ªSnapshotº function.
This records the measured values and is effective in the diag-
nosis of intermittent problems.
Please refer to the LEXUS hand±held tester/LEXUS break±
out±box operator's manual for further details.
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±77
WhereEverybodyKnowsYourName

ECU DATA MONITOR USING LEXUS HAND±HELD TESTER
1. Hook up the LEXUS hand±held tester to the DLC2.
2. Monitor the ECU data by following the prompts on the testerscreen.
HINT: LEXUS hand±held tester has a ªSnapshotº function
which records the monitored data.
Please refer to the LEXUS hand±held tester operator's
manual for further details.
Diagnostic Trouble Code of Speed Sensor Check Function
 Code No.\
\
Diagnosis Trouble Area 

71
\


\
Low output voltage of right front speed sensor
 



Right front speed sensor
 
71
\
\
Low output voltage of right front speed sensor
 
Sensor installation
 72\
\
Low output voltage of left front speed sensor 
Left front speed sensor
 72\
\
Low output voltage of left front speed sensor 
Sensor installation
 
73
\
\
Low output voltage of right rear speed sensor
 
Right rear speed sensor
 73\
\
Low output voltage of right rear speed sensor 
Sensor installation
 
74
\
\
Low output voltage of left rear speed sensor
 
Left rear speed sensor 74\
\
Low output voltage of left rear speed sensor 
Sensor installation 

75
\


\
Abnormal change in output voltage of right front speed
sensor 



Right front speed sensor rotor
 

76
\


\
Abnormal change in output voltage of left front speed
sensor 



Left front speed sensor rotor
 

77
\


\
Abnormal change in output voltage of right rear speed
sensor 



Right rear speed sensor rotor
 

78\


\
Abnormal change in output voltage of left rear speed
sensor 



Left rear speed sensor rotor
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)BR±81
WhereEverybodyKnowsYourName

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

DTC11, 12ABS Solenoid Relay Circuit
CIRCUIT DESCRIPTION
This relay supplies power to each ABS solenoid. After the ignition switch is\
turned on, if the initial check is OK,
the relay goes on.
DTC No.DTC Detecting ConditionTrouble Area
11
Conditions (1) and (2) continue for 0.2 sec. or more:
(1) ABS solenoid relay (SR) terminal voltage: Battery
positive voltage
(2) Solenoid relay monitor (AST) terminal voltage: 0V
ABS solenoid relay

Open or short in ABS solenoid relay circuit

ECU
12
Conditions (1) and (2) continue for 0.2 sec. or more:
(1) ABS solenoid relay (SR) terminal voltage: 0V
(2) Solenoid relay monitor (AST) terminal voltage: Bat- tery positive voltage
ABS solenoid relay

B+ short in ABS solenoid relay circuit

ECU
Fail safe function: If trouble occurs in the solenoid relay circuit, th\
e ECU cuts off current to the solenoid
relay and prohibits ABS control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±94±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName

OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals 1 and 2 of R/B No. 6 (For ABS solenoid relay\
).
C
OK
PRemove ABS solenoid relay from R/B No. 6.
Measure voltage between terminals 1 and 2 of R/B No.
6 (for ABS solenoid relay).
Voltage: 10 ± 14 V
Check and repair harness or connector.
2Check continuity between terminal 3 or R/B No. 6 (for ABS solenoid relay) a\
nd terminal AST of
ABS (& TRAC) ECU.
C
OK
Hint
Check continuity between 3 of R/B No. 6 (for ABS sole-
noid relay) and terminal AST of ABS (& TRAC) ECU.
Continuity
There is a resistance of 4 ~ 6
between terminals BS
and AST of ABS actuator.
Repair or replace harness or ABS actuator.
BR±96
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName

OKNG
OKNG
3Check ABS solenoid relay.
C
OK
P
C
OK
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.
4Check for open and short in harness and connector between ABS solenoid r\
elay 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±97
WhereEverybodyKnowsYourName

DTC13, 14ABS Motor Relay Circuit
CIRCUIT DESCRIPTION
The ABS motor relay supplies power to the ABS pump motor. While the ABS is activate the ECU switches the
motor relay ON and operates the ABS pump motor.
DTC No.DTC Detecting ConditionTrouble Area
13
Conditions (1) and (2) continued for 0.2 sec. or more:
(1) ABS motor relay (MR) terminal voltage: Battery positive voltage
(2) Motor relay monitor (MT) terminal voltage: 0V

ABS motor relay

Open or short in ABS motor relay circuit

ECU
14
Conditions (1) and (2) continued for 4 sec. or more:
(1) ABS motor relay (MR) terminal voltage: 0V
(2) Motor relay monitor (MT) terminal voltage: Battery positive voltage

ABS motor relay

B+ short in ABS motor relay circuit.

ECU
Fail safe function: If trouble occurs in the motor relay circuit, the ECU cuts off the current to the solenoid
relay and prohibits ABS control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±98±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName

OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal 1 of ABS motor relay and body ground.
C
OK
PRemove ABS motor relay from R/B No. 6.
Measure voltage between terminal 1 of ABS 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 ABS motor relay) and terminal MT of ABS
(& TRAC) ECU.
C
OK
Hint
Check continuity between terminal 2 or R/B No. 6 (for
ABS motor relay) and terminal MT of ABS (& TRAC)
ECU.
Continuity
There is a resistance of 4 ± 6 between terminals BM and
MT for ABS actuator.
Repair or replace harness or ABS actuator.
BR±100
±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
WhereEverybodyKnowsYourName