1991 LEXUS SC400 power steering

ABBREVIATIONS USED IN THIS
MANUAL
ABS Anti±Lock Brake System J/B Junction Block
A/C Air Conditioner LED Light Emitting Diode
ALR Automatic Locking Retractor LH Left±Hand
APPROX. Approximation LHD Left±Hand Drive
A/T, ATM Automatic Transmission LLC Long Life Coolant (Year Around Coolant)
ATF Automatic Transmission Fluid Max. Maximum
BTDC Before Top Dead Center Min. Minimum
BVSV Bimetal Vacuum Switching Valve MP Multipurpose
CALIF. Vehicles Sold in California N Neutral
CB Circuit Breaker OD, O/D Overdrive
DOHC Double Over Head Cam O/S Oversize
DP Dash Pot P & BV Proportioning and Bypass Valve
ECT Electronic Controlled Transmission PCV Positive Crankcase Ventilation
ECU Electronic Controlled Unit PS Power Steering
EFI Electronic Fuel Injection RH Right±Hand
EGR Exhaust Gas Recirculation RL Rear Left
ELR Emergency Locking Retractor RR Rear Right
EPR Evaporator Pressure Regulator RR, Rr Rear
ESA Electronic Spark Advance SRS Supplemental Restraint System
EVAP Evaporative (Emission Control) SSM Special Service Materials
EX Exhaust (manifold, valve) SST Special Service Tools
Ex. Except STD Standard
FIPG Formed in Place Gasket SW Switch
FL Front Left TDC Top Dead Center
FL Fusible Link TDCL Total Diagnostic Communication Link
FPU Fuel Pressure Up Temp. Temperature
FR Front Right TRAC Traction Control System
FR, Fr Front TWC Three±Way Catalyst
HAC High Altitude Compensation VSV Vacuum Switching Valve
IG Ignition VTV Vacuum Transmitting Valve
IN Intake (manifold, valve) w/ With
INT Intermittent w/o Without
ISC Idle Speed Control
IN±34±
INTRODUCTION Abbreviations Used in This Manual
WhereEverybodyKnowsYourName

When the negative (±) terminal cable is disconnected from
the battery, memory of the clock and audio systems will be
cancelled. So before starting work, make a record of the con-
tents memorized by each memory system. Then when work
is finished, reset the clock and audio systems as before.
When the vehicle has power tilt and power telescopic steer-
ing, power seat, power outside rear view mirror and power
shoulder belt anchorage, which are all equipped with
memory function, it is not possible to make a record of the
memory contents. So when the operation is finished, it will be
necessary to explain this fact to the customer, and ask the
customer to adjust the features and reset the memory.
To avoid erasing the memory of each memory system, never
use a back±up power supply from outside the vehicle.
3. Even in cases of a minor collision where the airbag does not deploy, the front airbag sensors and the steering wheel pad
should be inspected. (See page AB±9)
4. Never use airbag parts from another vehicle. When replacing parts, replace them with new parts.
5. Before repairs, remove the airbag sensors if shocks are likely
to be applied to the sensors during repairs.
6. The center airbag sensor assembly contains mercury. After
performing replacement, do not destroy the old part. When
scrapping the vehicle or replacing the center airbag sensor
assembly itself, remove the center airbag sensor assembly
and dispose of it as toxic waste.
7. Never disassemble and repair the front airbag sensors, center airbag sensor assembly or steering wheel pad in order
to reuse it.
8. If the front airbag sensors, center airbag sensor assembly or steering wheel pad have been dropped, or if there are cracks,
dents or other defects in the case, bracket or connector,
replace them with new ones.
9. Do not expose the front airbag sensors, center airbag sensor assembly or steering wheel pad directly to hot air or flames.
10. U s e a v o l t / o h m m e t e r w i t h h i g h i m pedance (10 kW/V
minimum) for troubleshooting of the electrical circuit.
11. Information labels are attached to the periphery of the airbag components. Follow the notices.
12. After work on the airbag system is completed, perform the
airbag warning light check (See page AB±30).
±
INTRODUCTION Precautions for Vehicles Equipped with SRS AirbagIN±9
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HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
A large number of ECU controlled systems are used in the LEXUS SC400. In \
general, the ECU controlled sys-
tem is considered to be a very intricate system requiring a high level o\
f technical knowledge and expert skill to
troubleshoot. However, the fact is that if you proceed to inspect the circuits one by one, trou\
bleshooting of these
systems is not complex. If you have adequate understanding of the system\
and a basic knowledge of electricity,
accurate diagnosis and necessary repair can be performed to locate and fix the p\
roblem. This manual is de-
signed through emphasis of the above standpoint to help service technici\
ans perform accurate and effective
troubleshooting, and is compiled for the following major ECU controlled \
systems:
Repair ManualSystemPage
1. EngineTR±1
Vl1
2. Automatic TransmissionAT±33
Vol. 13. Anti±Lock BrakeBR±43
4. Traction ControlBR±139
5. Steering Column Electronic ControlSR±22
6. SRS AirbagAB±25
7. Power Seat ControlBE±265
Vl2
8. Door Lock ControlBE±347
Vol. 29. Theft DeterrentBE±381
10. Wireless Door Lock ControlBE±425
11. Cruise ControlBE±459
12. Air ConditionerAC±21
The troubleshooting procedure and how to make use of it are described on\
the following pages.
±
INTRODUCTION How to Troubleshoot ECU Controlled SystemsIN±15
WhereEverybodyKnowsYourName

EVAPORATOR
REMOVAL OF EVAPORATOR
1. DISCONNECT NEGATIVE (±) CABLE FROM BATTERY
2. RECOVER REFRIGERANT IN REFRIGERATION SYSTEMSee page AC±16
3. REMOVE ABS ACTUATOR
See page BR±48
4. REMOVE LIQUID TUBE AND SUCTION TUBE Remove two bolts and both tubes.
5. REMOVE EQUALIZER TUBE FROM EPR
Remove the bole and the tube.
NOTICE: Cap the open fittings immediately to keep mois-
ture out of the system.
6. REMOVE UNDER COVER GLOVE BOX AND SIDE AIR DUCT
7. DISCONNECT CONNECTORS AND REMOVE POWER STEERING RELAY BOX COOLING FAN COMPUTER AND
TRC COMPUTER
AC±122
±
AIR CONDITIONING SYSTEM Evaporator
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DISPOSAL OF STEERING WHEEL
PAD (WITH AIRBAG)
When scrapping vehicles equipped with an airbag system or dis-
posing of a steering wheel pad (with airbag), always first deploy
the airbag in accordance with the procedure described below.
If any abnormality occurs with the airbag deployment, contact the
SERVICE DEPT. of TOYOTA MOTOR SALES, U.S.A., INC..
Never dispose of a steering wheel pad which has an
undeployed airbag.
When disposing of a steering wheel pad with an airbag deployed
in a collision, follow the same procedure given under ªAIRBAG
DEPLOYMENT PROCEDURE (WHEN SCRAPPING THE VE-
HICLE), part 5, DISPOSAL OF STEERING WHEEL PAD (WITH
AIRBAG)º (See page AB±93).
PRECAUTIONS FOR AIRBAG DEPLOYMENT
1. The airbag produces a sizeable exploding sound when
it deploys, so perform the operation out±of±doors and
where it will not create a nuisance to nearby residents.
2. When deploying the airbag, always use the specified
SST; SRS AIRBAG DEPLOYMENT TOOL (SST
09082±00700). Perform the operation in a place away
from electrical noise.
3. When deploying an airbag, perform the operation from at least 10 m (33 ft) away from the steering wheel pad.
4. The steering wheel pad is very hot when the airbag is deployed, so leave it alone for at least 30 minutes after
deployment.
5. Use gloves and safety glasses when handling a steering
wheel pad with deployed airbag.
6. Always wash your hands with water after completing the operation.
7. Do not apply water, etc. to a steering wheel pad with deployed airbag.
AIRBAG DEPLOYMENT PROCEDURE
(WHEN SCRAPPING VEHICLE)
HINT: Have a battery ready as the power source to deploy the
airbag.
1. DISCONNECT NEGATIVE (±) TERMINAL CABLE FROM BATTERY
CAUTION: Work must be started after approx. 30 sec-
onds or lo nger from the time the ignition switch is turned
to the LOCK position and the negative (±) terminal cable
is disconnected from the battery (See page AB±2).
±
SRS AIRBAG Disposal of Steering Wheel Pad (with Airbag)AB±91
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5. DISPOSAL OF STEERING WHEEL PAD (WITH AIRBAG)CAUTION:
w The steering wheel pad is very hot when the airbag is
deployed, so leave it alone for at least 30 minutes after
deployment.
w Use gloves and safety glasses when handling a steering
wheel pad with deployed airbag.
w Do not apply water, etc. to a steering wheel pad with
deployed airbag.
w Always wash your hands with water after completing the
operation.
(a) When scrapping a vehicle, deploy the airbag and scrap
the vehicle with the steering wheel pad still installed.
(b) When moving a vehicle for scr apping which has a
steering wheel pad with deployed airbag, use gloves
and safety glasses.
AIRBAG DEPLOYMENT PROCEDURE
(PROCEDURE FOR DISPOSAL OF
STEERING WHEEL PAD ONLY)
When disposing of the steering wheel pad (with airbag)
only, never use the customer's vehicle to deploy the
airbag.
Remove the steering wheel pad from the vehicle and be sure
to follow the procedure given below when deploying the
airbag.
HINT: Have a battery ready as the power source to deploy the
airbag.
1. REMOVE STEERING WHEEL PAD (SEE PAGE AB±16)
CAUTION:
wWhen removing the steering wheel pad (with
airbag), work must be started after approx. 30
seconds or longer from the time the ignition switch
is turned to the LOCK position and the negative (±)
terminal cable is disconnected from the battery.
w When storing the steering wheel pad, keep the upper
surface of the pad facing upward.
2. REMOVE STEERING WHEEL PAD CONNECTOR
Remove the connector on the steering wheel pad rear
surface from the inflater cover.
±
SRS AIRBAG Disposal of Steering Wheel Pad (with Aribag)AB±93
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GENERAL DESCRIPTION
The LEXUS SC400 is equipped with an SRS (Supplemental Restraint System) a\
irbag.
Failure to carry out service operations in the correct sequence could cause the\
airbag system to unex-
pectedly deploy during servicing, possibly leading to a serious accident.
Further, if a mistake is made in servicing the airbag system, it is possible the\
airbag may fail to operate
when required.
Before performing servicing (including removal or installation of parts, insp\
ection or replacement), be
sure to read the following items carefully, then follow the correct procedure described in the repair
manual.
1. Malfunction symptoms of the airbag system are difficult to confirm, so the diagnostic codes become themost important source of information when troubleshooting.
When troubleshooting the airbag system, always inspect the diagnostic co\
des before disconnecting the
battery (See page AB±25).
2. Work must be started after approx. 20 seconds or longer from the time the ig\
nition switch is turned to the LOCK position and the negative (±) terminal cable is disconnec\
ted from the battery. (The
airbag system is equipped with a back±up power source so that if work is sta\
rted within 20 seconds
of disconnecting the negative (±) terminal cable of the battery, the airbag may be deployed.)
When the negative (±) terminal cable is disconnected from the battery, memory of the clock and audio sys-
tems will be cancelled. So before starting work, make a record of the conten\
ts memorized by the audio
memory system. Then when work is finished, reset the audio systems as before a\
nd adjust the clock. When
the vehicle has power tilt and power telescopic steering, power seat, power \
outside rear view mirror and
power shoulder belt anchorage, which are all equipped with memory function, it\
is not possible to make
a record of the memory contents. So when the work is finished, it will be\
necessary to explain this fact to
the customer, and ask the customer to adjust the features and reset the memory. To avoid erasing the
memory of each memory system, never use a back±up power supply from outside\
the vehicle.
3. Even in cases of a minor collision where the airbag does not deploy, the front airbag sensors and
the steering wheel pad should be inspected (See page AB±9).
4. Never use airbag parts from another vehicle. When replacing parts, replace them with new parts.
5. Before repairs, remove the airbag sensors if shocks are likely to be applied to the sensors during repairs.
6. Never disassemble and repair the front airbag sensors, center airbag sensor a\
ssembly or steering
wheel pad in order to reuse it.
7. If the front airbag sensors, center airbag assembly or steering wheel pa\
d have been dropped, or if there are cracks, dents or other defects in the case, bracket or conn\
ector, replace them with new
ones.
8. Do not expose the front airbag sensors, center airbag sensor assembly or\
steering wheel pad directly to hot air or flames.
9. Use a volt/ohmmeter with high impedance (10 kW/V minimum) for troubleshoo\
ting of the electrical circuit.
10. Information labels are attached to the periphery of the airbag components. Follow t\
he instructions
on the notices.
11. After work on the airbag system is completed, perform the airbag warning\
light check (See page AB±30 ).
AB±2
SRS AIRBAG
± General Description
WhereEverybodyKnowsYourName

DIAGNOSTIC CODES
CodeNo.Blink PatternDiagnosisTrouble AreaAIRBAG
Warning Light
(Nor

System normal±OFF
(Nor-
mal)
Source Voltage drop
Battery

Center airbag sensor assemblyON
11

Short in squib circuit
(to ground)

Front airbag sensor
malfunction

Flower sensor malfunction
Steering wheel pad (squib)

Front airbag sensor

Spiral cable

Center airbag sensor assembly

Wire harness
ON
12

Short in squib circuit
(to +B)
Steering wheel pad (squib)

Front airbag sensor

Spiral cable

Center airbag sensor assembly

Wire harness
ON
13

Short in squib circuit
(between D+ wire harness
and D± wire harness)

Steering wheel pad (squib)

Spiral cable

Center airbag sensor assembly

Wire harness
ON
14

Open in squib circuit
Steering wheel pad (squib)

Spiral cable

Center airbag sensor assembly

Wire harness
ON
15

Open in front airbag
sensor circuit
Front airbag sensor

Center airbag sensor assembly

Wire harness
ON
22

Airbag warning light
system malfunction
Airbag warning light

Center airbag sensor assembly

Wire harness
ON
31

Center airbag sensor
assembly malfunction

Center airbag sensor assemblyON
41

Malfunction stored in
memory

(Center airbag sensor assembly)ON
HINT:
w When the airbag warning light remains lit up and the diagnostic code in the n\
ormal code, this means a
source voltage drop.
This malfunction is not stored in memory by the center airbag sensor ass\
embly and if the power source
voltage returns to normal, after approx. 10 seconds the airbag warning l\
ight will automatically go out.
w Code 22 in recorded when a malfunction occurs in the airbag warning light sy\
stem. If an open malfunction
occurs in the airbag warning light system, the airbag warning light does not l\
ight up, so that until the
mal±function is repaired, the diagnostic codes (including code 22) cannot be confi\
rmed.
w When a malfunction occurs in the airbag system, malfunction codes 11 to 31 are output. After repairing
the malfunction indicated by malfunction codes 11 to 31, codes 11 to 31 are cleared from the memory, but
code 41 is output instead. Once the malfunction has been detected, the airba\
g warning light will remain
lit up until code 41 is cleared, even though the malfunction has been re\
paired.
w When 2 or more codes are indicated, the lowest numbered code will appear\
first.
w If a code not listed on the chart is displayed, then the center airbag s\
ensor assembly is faulty. AB±31
SRS AIRBAG
± Troubleshooting
WhereEverybodyKnowsYourName