Lexus SC300 / Lexus SC400. Manual - part 238

NO

YES

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Is 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.

2

Check voltage between terminal VTH of TRAC ECU and body ground.

C

OK

P

1.

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 with out interrup-
tion.

Go to step 



.

3

Check for open and short in harness and connector between terminal VTH of 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

NG

OK

NG

OK

4

Check voltage between terminal VTO1 of ECM and body ground with TRAC ECU connector dis-
connected.

C

OK

P

1.

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 throttle valve is fully closed
and fully opened.

Check and replace TRAC ECU.

5

Check 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)

OK

NG

NG

OK

6

Check 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

).

7

Check voltage between terminal IDL1 of TRAC ECU and body ground.

C

OK

P

Turn 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

NG

OK

OK

NG

8

Check voltage between terminal IDL1 of TRAC ECU connector and body ground with TRAC ECU
connector disconnected.

C

OK

P

1.

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>

9

Check for open and short in harness and connector between terminal IDL1 of TRAC ECU and
ECM (See page 

IN–33

).

Repair or replace harness or connector.

BR–206

–

BRAKE SYSTEM

TRACTION CONTROL SYSTEM (TRAC)