LEXUS SC400 1991 Service Repair Manual

±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±185
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WIRING DIAGRAM
IN±33).
DTC24TRAC Sub±Throttle Actuator Circuit
CIRCUIT DESCRIPTION
The sub±throttle actuator operates in accordance with signals from the E\
CU, controlling the opening and
closing of the sub±throttle valve.
DTC No.DTC Detecting ConditionTrouble Area
24Open or short in sub±throttle actuator circuit

TRAC fuse

Open or short in BM circuit.

Sub±throttle actuator.

Open or short in sub±throttle actuatorcircuit.

ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±186±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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OKNG
OKNG
INSPECTION PROCEDURES
1Check TRAC fuse.
C
OK
PRemove TRAC fuse from R/B No. 2.
Check continuity of TRAC fuse.
Continuity
Check for short in all harness and components con-
nected to TRAC fuse (See attached wiring diagram).
2Check voltage between terminals BM and GND or TRAC ECU.
C
OK
PRemove TRAC ECU with connectors still connected.
Measure voltage between terminals BM and GND of
TRAC ECU.
Voltage: 10 ± 14 V
Check and repair harness or connector.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±187
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OKNG
OKNG
3Check sub±throttle actuator.
C
OK
PDisconnect sub±throttle actuator connector.
Check continuity between each terminal of sub±throttle
actuator connector shown below.
Replace sub±throttle actuator.
4Check for open and short in harness and connector between TRAC ECU and sub±\
throttle actua-
tor (See page IN±33).
Repair or replace harness or connector.
Check and replace TRAC ECU.
BR±188±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
WhereEverybodyKnowsYourName

WIRING DIAGRAM
DTC25, 26, 27TRAC Sub±Throttle Valve
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
25
The difference between the sub±throttle sensor signal
voltage and the voltage required by the step count is 1
V or more.

Sub±throttle actuator.

Throttle body (sub±throttle valve is truck or operation is
faulty).

Sub±throttle position sensor.

Open or short in sub±throttle position sensor circuit.

ECM

TRAC ECU
26
Even when sub±throttle valve is driven to the fully open
position, input voltage at terminal VSH does not come
within range of the specifications 3 ~ 4.5 V.

Sub±throttle actuator.

Throttle body (sub±throttle valve is truck or operation is
faulty).

Sub±throttle position sensor.

Open or short in sub±throttle position sensor circuit.

ECM

TRAC ECU
27When input voltage at ECU terminal VSH is less than
the specification by about 2.5 V for 0.2 sec. or more.

Sub±throttle actuator (return spring is disconnected).

Sub±throttle position sensor.

Open or short in sub±throttle position sensor circuit.

ECM

TRAC ECU
C
OK
Hint
PRemove air cleaner and duct.
Open and close the sub±throttle valve manually and
check the condition during operation.
The valve should operate smoothly without catch-
ing.
If sub±throttle actuator, sub±throttle valve, sub±throttle
position sensor and harness are free from any defect,
ECM may be defective. If ECM is free from any defect,
TRAC ECU may be defective.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±189
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The speed sensor detects the wheel speed and sends the ap-
propriate signals to the ECU. These signals are used for control
of both the ABS and TRAC control systems. The front and rear
rotors each have 48 serrations. When the rotors rotate, the mag-
netic field emitted by the permanent magnet in the speed sensor
generates an AC voltage. Since the frequency of this AC voltage
changes in proportion to the speed of the rotors (wheels), the
frequency is used by the ECU to detect the speed of each wheel.
BR3583
BR3582
DTC31, 32,
33, 34Speed Sensor Circuit
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
31, 32,
33, 34
Detection of any of conditions (1) through (3):
(1) At vehicle speed of 10 km/h (6 mph) or more, pulses are not input for 5 sec.
(2) Momentary interruption of the vehicle speed sen- sor signal occurs at least 7 times in the time be-
tween switching the ignition switch ON and switch-
ing it OFF.
(3) Abnormal fluctuation of speed sensor signals with the vehicle speed 20 km/h (12 mph) or more.

Right front, left front, right rear and left rear
speed sensor.

Open or short in each speed sensor circuit.

ECU
Hint: DTC No. 31 is for the right front wheel speed sensor.
DTC No. 32 is for the left front wheel speed sensor.
DTC No. 33 is for the right rear wheel speed sensor.
DTC No. 34 is for the left rear wheel speed sensor.
Fail safe function: If trouble occurs in the speed sensor circuit, the E\
CU prohibits TRAC control.
BR±190
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
WhereEverybodyKnowsYourName

BR±120
WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±191
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IN±33).
WIRING DIAGRAM
DTC41IG Power Source Circuit
CIRCUIT DESCRIPTION
This is the power source for the ECU and becomes power source for the CPU an\
d actuators.
DTC No.DTC Detecting ConditionTrouble Area
41
When either of the following (1) or (2) is detected:
(1) Voltage at ECU terminal IG is less than 9.5 V for more than 10 sec. while engine speed is 500 rpm
or higher.
(2) Voltage at ECU terminal IG is more than 17 V for more than 5 sec.

Battery

IC regulator

Open or short in power source circuit

ECU
Fail safe function: If trouble occurs in the power source circuit, the E\
CU prohibits TRAC control.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±192±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
WhereEverybodyKnowsYourName

OKNG
NGOK
OKNG
INSPECTION PROCEDURE
1Check battery positive voltage.
Voltage: 10 ± 14 VCOK
Check and repair the charging system.
2Check voltage between terminals IG and GND of TRAC ECU connector.
C
OK
P1. Remove TRAC ECU with connectors still con-nected.
2. Turn ignition switch on.
Measure voltage between terminals IG and GND of
TRAC ECU connector.
Voltage: 10 ± 14 V
Check and replace TRAC ECU.
3Check continuity between terminals GND of TRAC ECU connector and body gr\
ound.
C
OK
Measure resistance between terminal GND or TRAC
ECU connector and body ground.
Resistance: 1
or less
Repair or replace harness or connector.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±193
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OKNG
4Check ECU±IG fuse.
C
OK
PRemove ECU±IG fuse from J/B No. 1.
Check continuity of ECU±IG fuse.
Continuity
Check for short in all the harness and components con-
nected to ECU±IG fuse (See attached wiring diagram).
Check for open in harness and connector between
TRAC ECU and battery (See page IN±33).
BR±194±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
WhereEverybodyKnowsYourName