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
Check for open in harness and connector between
ECU and door courtesy switch LH connector.
–
STEERING
STEERING COLUMN
SR–99
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
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
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
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STEERING
POWER STEERING
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