ect LEXUS SC300 1991 Service Repair Manual

SR±52).
BE±168
.
WIRING DIAGRAM
Park/Neutral Position Switch Circuit
CIRCUIT DESCRIPTION
The park/neutral position switch detects whether the shift position is in P\
position or in another position,
and sends a signal to the ECU.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±94±
STEERING STEERING COLUMN
WhereEverybodyKnowsYourName

OKNG
NGOK
INSPECTION PROCEDURE
1Check shift position indicator.
Check that ªPº lights up on the shift indicator when P position is shif\
ted into, and that ªPº is extin-
guished when shifting into another position.P
Check and repair shift position indicator circuit (See
page BE±168 ).
2Check voltage between terminal P of ECU connector and body ground.
C
OK
PRemove ECU with connectors still connected.
1. Turn ignition switch on.
2. Measure voltage between terminal P of ECU con-
nector and body ground when the shift lever is oper-
ated.
Proceed to next circuit inspection shown on matrix chart
(See page SR±52).
Check for open in harness and connectors be-
tween ECU and [IK1] connector.
±
STEERING STEERING COLUMNSR±95
WhereEverybodyKnowsYourName

WIRING DIAGRAM
CIRCUIT INSPECTION
Parking Brake Switch Circuit
CIRCUIT DESCRIPTION
When the parking brake is operating, the parking brake switch sends a signal\
to the ECU. When this signal
is input to the ECU during tilt & telescopic, the ECU cancels tilt & tel\
escopic.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±96±
STEERING STEERING COLUMN
WhereEverybodyKnowsYourName

OKNG
NGOK
NGOK
OKNG
INSPECTION PROCEDURE
1Check operation of brake warning light.
Check that the brake warning light in the instrument panel comes on when the \
parking brake is opera-
tion with the engine running, and the light goes off when the parking brake is not operating.C
Check brake warning light circuit.
2Input signal check.
C
OK
1. See input signal check.
2. Check the indicator light when the parking brake isoperating.
The indicator light goes off when the parking brake
is operating.
Proceed to next circuit inspection shown on matrix
chart.
3Check voltage between terminal PKB of tilt & telescopic ECU connector and bod\
y ground.
C
OK
PRemove tilt & telescopic ECU with connectors still con-
nected.
1. Turn ignition switch ON.
2. Measure voltage between terminal PKB of tilt & telescopic ECU connector and body ground, when
the parking brake lever is operating.
Proceed to next circuit inspection shown on matrix
chart.
4Check for open in harness and connector between tilt & telescopic ECU and brak\
e warning light
(See page IN±33).
.
Repair or replace harness or connector
Check and replace tilt & telescopic ECU.
±
STEERING STEERING COLUMNSR±97
WhereEverybodyKnowsYourName

OKNG
NGOK
INSPECTION PROCEDURE
1Check 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.
2Check voltage between terminal DSW of ECU connector and body ground.
C
PRemove 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 COLUMNSR±99
WhereEverybodyKnowsYourName

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.)
 Ignition key Unlock Warning Switch UWSW Voltage
 

Out 

Opened 

10±14 V
 In Closed Below 1 V
DIAGNOSTIC CHARTDIAGNOSTIC CHART
SR±100±
STEERING STEERING COLUMN
WhereEverybodyKnowsYourName

NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal UWSW of ECU connector and body ground
C
OK
PRemove 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).
2Check unlock warning switch.
C
OK
PDisconnect 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.
3Check 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 COLUMNSR±101
WhereEverybodyKnowsYourName

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 r\
oad 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 ste\
ering effort. Consequently,
the engine is used to drive a pump to develop fluid pressure, and this p\
ressure 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
WhereEverybodyKnowsYourName

OPERATION
NEUTRAL (STRAIGHT±AHEAD) POSITION
SR0NU±01
Fluid from the pump is sent to the control valve. If the control valve is in \
the neutral position, all the fluid
will flow through the control valve into the relief port and back to the pu\
mp. At this time, hardly any pressure
is created and because the pressure on the cylinder piston is equal on bot\
h sides, the piston will not move
in either direction.
WHEN TURNING
When the steering main shaft is turned in either direction, the control valv\
e also moves, closing one of the
fluid passages. The other passage then opens wider, causing a change in fluid flow volume and, at the
same time, a differential pressure is created between both sides of the piston. Conseque\
ntly, the piston
moves in the direction of the lower pressure so that the fluid in the cylinder is forced back to the pump
through the control valve.
±
STEERING POWER STEERINGSR±103
WhereEverybodyKnowsYourName

SERVICE HINT
Troubles with the power steering system are usually concerned with hard steering due to the fact that there
is no assistance. In such cases, before attempting to make repairs, it i\
s necessary to determine whether
the trouble lies with the pump or with the gear housing. To do this, an on±vehicle inspection, can be made
by using a pressure gauge.
ON±VEHICLE INSPECTION Power steering is a hydraulic device and problems are normally due to insufficient fluid pressure acting on
the piston. This could be caused by either the pump not producing the speci\
fied fluid pressure or the control
valve in the gear housing not functioning properly so that the proper fluid p\
ressure can not be obtained.
If the fault lies with the pump, the same symptoms will generally occur wh\
ether the steering wheel is turned
fully to the right or left. On the other hand, if the fault lies with the con\
trol valve, there will generally be a
difference between the amount of assistance when the steering wheel is turned to th\
e left and right, causing
harder steering. However, if the piston seal of the power cylinder is worn, there will be a loss of f\
luid pressure
whether the steering wheel is turned to the right or left and the symptoms will\
be the same for both.
Before performing an on±vehicle inspection, a check must first be made to c\
onfirm that the power steering
system is completely free of any air. If there is any air in the system, the volume of this air will change \
when
the fluid pressure is raised, causing a fluctuation in the fluid pressure s\
o that the power steering will not
function properly. To determine if there is any air in the system, check to see if there is \
a change of fluid
level in the reservoir tank when the steering wheel is turned fully to t\
he right or left.
For example, if there is air in the system, it will be compressed to a smal\
ler volume when the steering wheel
is turned, causing a considerable drop in the fluid level. If the system is free of air, there will be very little
change in the level even when the fluid pressure is raised. This is beca\
use the fluid, being a liquid, does
not change volume when compressed. The little change in the fluid level is d\
ue to expansion of the hoses
between the pump and gear housing when pressure rises. Also, air in the system will sometimes result in
an abnormal noise occurring from the pump or gear housing when the steerin\
g wheel is fully turned in either
direction.
This on±vehicle inspection must be performed every time to ensure tha\
t the power steering system is work-
ing properly after overhauling or repairing the pump or gear housing.
SR±104±
STEERING POWER STEERING
WhereEverybodyKnowsYourName