Lexus SC300 / Lexus SC400. Manual - part 740

OK

NG

NG

OK

INSPECTION PROCEDURE

1

Check operation of door courtesy light LH.

Check that door courtesy light comes on when the driver’s door is opened, and that the light goes
off when the driver’s door is closed.

P

Check and repair door courtesy light circuit.

2

Check voltage between terminal DSW of ECU connector and body ground.

C

P

Remove ECU with connectors still connected.

Measure voltage between terminal DSW of ECU con-
nector and body ground when the driver’s door is
opened and closed.

Proceed to next circuit inspection shown on matrix chart
(See page  

SR–52

).

Check for open in harness and connector between
ECU and door courtesy switch LH connector.

–

STEERING

STEERING COLUMN

SR–99

SR–52

).

 

IN–33

).

Unlock Warning Switch Circuit

CIRCUIT DESCRIPTION

Whether or not the key is inserted in the key cylinder is detected and a signal is sent to the ECU.
(The switch is ON (closed) when the ignition key is inserted.)

ÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑ

Ignition key

ÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑ

Unlock Warning Switch

ÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑ

UWSW Voltage

ÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑ

Out

ÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑ

Opened

ÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑ

10–14 V

ÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑ

In

ÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑ

Closed

ÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑ

Below 1 V

DIAGNOSTIC CHART

DIAGNOSTIC CHART

SR–100

–

STEERING

STEERING COLUMN

NG

OK

OK

NG

OK

NG

INSPECTION PROCEDURE

1

Check voltage between terminal UWSW of ECU connector and body ground

C

OK

P

Remove ECU with connectors still connected.

Measure voltage between terminal UWSW of ECU con-
nector and body ground with the ignition key inserted,
or removed.

Proceed to next circuit inspection shown on matrix chart
(See page 

SR–52

).

2

Check unlock warning switch.

C

OK

P

Disconnect unlock warning switch connector.

Measure resistance between terminals 9 and 10 of un-
lock warning switch connector with the ignition key in-
serted or removed.

Replace unlock warning switch.

3

Check harness and connector between ECU and unlock warning switch (See page  

IN–33

).

Repair or replace harness or connector.

Check and replace ECU.

–

STEERING

STEERING COLUMN

SR–101

POWER STEERING

DESCRIPTION

SR0KG–03

The Progressive Power Steering (PPS) is basically a power rack and pinion gear with a rotary control valve.
The PPS varies the amount of hydraulic assistance with respect to vehicle road speed. In addition the unit
incorporates an electronically controlled hydraulic reaction chamber.

PRINCIPLES OF POWER STEERING

Power steering is a hydraulic device which utilizes engine power to reduce steering effort. Consequently,
the engine is used to drive a pump to develop fluid pressure, and this pressure acts on a piston within the
power cylinder so that the piston assists the rack effort. The amount of this assistance depends on the ex-
tent of pressure acting on the piston. Therefore, if more steering force is required, the pressure must be
raised. The variation in the fluid pressure is accomplished by a control valve which is linked to the steering
main shaft.

SR–102

–

STEERING

POWER STEERING