Lexus SC300 / Lexus SC400. Manual - part 234

OK

NG

OK

NG

INSPECTION PROCEDURES

1

Check TRAC fuse.

C

OK

P

Remove 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

).

2

Check voltage between terminals BM and GND or TRAC ECU.

C

OK

P

Remove 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

OK

NG

OK

NG

3

Check sub–throttle actuator.

C

OK

P

Disconnect sub–throttle actuator connector.

Check continuity between each terminal of sub–throttle
actuator connector shown below.

Replace sub–throttle actuator.

4

Check 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)

WIRING DIAGRAM

DTC

25, 26, 27 TRAC Sub–Throttle Valve

CIRCUIT DESCRIPTION

DTC No.

DTC Detecting Condition

Trouble 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

27

When 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

P

Remove 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

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

DTC

31, 32,

33, 34

Speed Sensor Circuit

CIRCUIT DESCRIPTION

DTC No.

DTC Detecting Condition

Trouble 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 ECU prohibits TRAC control.

BR–190

–

BRAKE SYSTEM

TRACTION CONTROL SYSTEM (TRAC)