ECU LEXUS SC400 1991 Service Repair Manual

NOYES
NGOK
OKNG
INSPECTION PROCEDURE
1Is diagnostic trouble code output for the engine?
Perform diagnostic trouble code check on page EG±523 or EG±305 .
Repair circuit indicated by the code output.
2Check voltage between terminal VTH of TRAC ECU and body ground.
C
OK
P1. Remove TRAC ECU with connectors still con-
nected.
2. Remove intake air duct.
3. Turn ignition switch on.
Measure voltage between terminal VTH of TRAC ECU
and body ground, when the main throttle valve is turned
from fully closed position to fully opened position by
hand
In addition, as the main throttle valve is turned, the
voltage should increase gradually w ith out interrup-
tion.
Go to step .
3Check for open and short in harness and connector between terminal VTH o\
f TRAC ECU and
terminal VTO1 of ECM (See page IN±33).
Repair or replace harness or connector.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±203
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NGOK
NGOK
4Check voltage between terminal VTO1 of ECM and body ground with TRAC ECU connector dis-
connected.
C
OK
P1. Connect the Check Harness A. (See page EG±542
or EG±328 ).
2. Disconnect the TRAC ECU connector.
3. Turn ignition switch on.
Measure voltage between terminal VTO1 or ECM and
body ground, when the main thro ttle valve is fully closed
and fully opened.
Check and replace TRAC ECU.
5Check voltage of terminal VTA1 of ECM (See page EG±608 or EG±388 ).
Check and replace ECM.
BR±204
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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OKNG
NGOK
6Check for open and short in harness and connector between terminal VTA1 of ECM and main
throttle position sensor (See page IN±33
).
Repair or replace harness or connector.
Adjust or replace main throttle position sensor
(See page EG±333 or EG±205 ).
7Check voltage between terminal IDL1 of TRAC ECU and body ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal IDL1 of TRAC ECU
and body ground, when the main throttle valve is fully
closed and fully opened.
Check and replace TRAC ECU.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±205
WhereEverybodyKnowsYourName

NGOK
OKNG
8Check voltage between terminal IDL1 of TRAC ECU connector and body ground with TRAC ECU
connector disconnected.
C
OK
P1. Disconnect the TRAC ECU connector.
2. Turn ignition switch on.
Measure voltage between IDL1 of TRAC ECU connec-
tor and body ground, when the main throttle valve is fully
closed and fully opened.
Check and replace TRAC ECU>
9Check for open and short in harness and connector between terminal IDL1 of TR\
AC ECU and
ECM (See page IN±33).
Repair or replace harness or connector.
BR±206
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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DTC47, 48Sub±Throttle Position Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the opening angle of the sub±throttle valve and sends the appropriate signals to the ECU.
If a trouble signal is input, the ECU prohibits TRAC control.
DTC No.DTC Detecting ConditionTrouble Area
47
When any of the following (1) through (3) is detected:
(1) Deviation of 5 steps or more to the closedside of the idle step during sub±throttleinitial check.
(2) Voltage at terminal IDL2 switch is OFF evenafter sub±throttle is driven to fully closedposition during
sub±throttle initial check 4.
(3) Voltage at terminal VSH is 1.45 V or morefor at least 0.15 sec. while idle switch is ON.

Sub±throttle position sensor

Open or short in IDL2 circuit

ECM

TRAC ECU
48
Either of the following (1) or (2) continues for atleast
0.12 sec.
(1) Input voltage of TRAC ECU terminal VSH:4.3 V or more.
(2) Input voltage of TRAC ECU terminal VSHis 0.2 V or less while IDL2 switch OFF.

Sub±throttle position sensor

Open or short in VSH circuit

ECM

TRAC ECU
BR±208±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
WhereEverybodyKnowsYourName

NOYES
NGOK
OKNG
INSPECTION PROCEDURE
1Is diagnostic trouble code output for the engine?
Perform diagnostic trouble code check on page EG±523 or EG±305 .
Repair circuit indicated by the code output.
2Check voltage between terminal VSH or TRAC ECU and body ground.
C
OK
P1. Remove TRAC ECU with connectors still con-
nected.
2. Remove intake air duct.
3. Disconnect step motor connector.
4. Turn ignition switch on.
Measure voltage between terminal VSH or TRAC ECU
and body ground, when the sub±throttle valve is turned
from fully opened position to fully closed position.
In addition, as the sub±throttle valve is turned, the
voltage should increase gradually w ith out interrup-
tion.
Go to step
.
3Check for open and short in harness and connector between terminal VSH of TRAC ECU and
terminal VTO2 of ECM (See page IN±33).
Repair or replace harness or connector.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±211
WhereEverybodyKnowsYourName

NGOK
NGOK
4Check voltage between terminal VTO2 of ECM and body ground with TRAC ECU connector dis-
connected.
C
OK
P1. Connect the Check Harness A. (See page EG±562
or EG±328 ).
2. Disconnect the TRAC ECU connector.
3. Turn ignition switch on.
Measure voltage between terminal VTO2 of ECM and
body ground, when the sub±throttle valve is fully closed
and fully opened.
Check and replace TRAC ECU.
5Check voltage of terminal VTA2 of ECM (See page EG±608 or EG±388 ).
Check and replace ECM.
BR±212
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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OKNG
NGOK
6Check for open and short in harness and connector between terminal VTA2 of ECM and sub±
throttle position sensor (See page IN±33
)
Repair or replace harness or connector.
Adjust or replace sub±throttle position sensor
(See page EG±333 or EG±205 ).
7Check voltage between terminal IDL2 of TRAC ECU and body ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal IDL2 or TRAC ECU
connector and body ground, when the sub±throttle
valve is fully closed and fully opened.
Check and replace TRAC ECU.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±213
WhereEverybodyKnowsYourName

NGOK
OKNG
8Check voltage between terminal IDL2 of TRAC ECU connector and body ground with TRAC ECU
connector disconnected.
C
OK
Hint
P1. Disconnect the TRAC ECU connector.
2. Turn ignition switch on.
Measure voltage between terminal IDL2 of TRAC ECM
connector and body ground, when the sub±throttle
valve is fully closed and fully opened.
Check and replace TRAC ECU.
9Check for open and short in harness and connector between terminal IDL2 of TR\
AC ECU and
ECM (See page IN±33).
Repair or replace harness or connector.
BR±214
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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IN±29).
WIRING DIAGRAM
DTC49Engine Communication Circuit
CIRCUIT DESCRIPTION
This circuit is used to send ignition timing retard request signals from the TRAC ECU to\
the ECM in order to retard
the engine ignition timing.
DTC No.DTC Detecting ConditionTrouble Area
49TR2 output voltage differs from TR2 monitorvoltage in
TRAC ECU.
Open or short in TR2 circuit

ECM

TRAC ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±216±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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