1991 LEXUS SC400 check engine

IDENTIFICATION INFORMATION
VEHICLE IDENTIFICATION NUMBER
This number is stamped on the vehicle identification number plate
at the top of the left instrument panel and is also on the certification
regulation label.A: Vehicle Identification Number
B: Vehicle Identification Number Plate
C: Certification Regulation Label
ENGINE SERIAL NUMBER
The engine serial number is stamped on the engine block as
shown.
GENERAL REPAIR INSTRUCTIONS
1. Use fender seat and floor covers to keep the vehicle clean
and prevent damage.
2. During disassembly, keep parts in the appropriate order to facilitate reassembly.
3. Observe the following:
(a) CAUTION: W ork must be started after approx. 20 seconds
or longer from the time the ignition switch is turned to the
ºLOCKº position and the negative (±) terminal cable is
disconnected from the battery (See page AB±2).
(b) B e fo re pe rfo rmin g ele ctrica l wo rk, disc onnect the
negative cable from the battery terminal.
(c) If it is necessary to disconnect the battery for inspection or repair, always disconnect the cable from the negative
(±) terminal which is grounded to the vehicle body.
(d) To prevent damage to the battery terminal post, loosen the terminal nut and raise the cable straight up without
twisting or prying it.
(e) Clean the battery terminal posts and cable terminals with a shop rag. Do not scrape them with a file or other
abrasive object.
(f) Install the cable terminal to the battery post with the nut loose, and tighten the nut after installation. Do not use
a hammer to tap the terminal onto the post.
(g) Be sure the covers for the positive (+) terminal and negative (±) terminal are properly in place.
4. Check hose and wiring connectors to make sure that they are
secure and correct.
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12. Observe the following precautions to avoid damage to theparts:
(a) Do not open the cover or case of the ECU unless
absolutely necessary (If the IC terminals are touched, the
IC may be destroyed by static electricity.).
(b) To pull apart electrical connectors, pull on the connectoritself, not the wires (See page BE±2).
(c) Be careful not to drop electrical components, such as sensors or relays. It they are dropped on a hard floor,
they should be replaced and not reused.
(d) When checking continuity at the wire connector, insert the tester probe carefully to prevent terminals from
bending.
(e) To disconnect vacuum hoses, pull on the end, not the middle of the hose.
(f) When steam cleaning an engine, protect the distributor,
coil and air filter from water.
(g) Ne ve r use an imp a ct wre n ch to re mo ve or in sta ll temperature switches or temperature sensors.
(h) When using a vacuum gauge, never force the hose onto
a connector that is too large. Use a step±down adapter
instead. Once the hose has been stretched, it may leak.
13. Tag hoses before disconnecting them: (a) When disconnecting vacuum hoses, use tags to identify
how they should be reconnected.
(b) After completing a job, double check that the vacuum hoses are properly connected. A label under the hood
shows the proper layout.
14. Installation of wheels The wheel assemblies are of the uni±directional type and
must be rotated only between the front and rear as illustrated.
Wheels are marked with turning direction indicators.
When installing the wheels, check the marks carefully and
install the wheel correctly.
15. Bleeding of traction control system When repairing the brake master cylinder or TRAC system,
bleed the air out of the TRAC system (See page BR±7).
CAUTION: Since the fluid is under high pressure, it could
spray out with great force, so be careful.
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TOTAL DIAGNOSTIC
COMMUNICATION LINK (TDCL)
The TDCL is provided inside the cabin (located under the left side
instrument panel) as a connector exclusively for diagnosis of data
from the engine, ECT, ABS, A/C, Airbag and Cruise Control Sys-
tem to improve serviceability. The check connector inside the en-
gine compartment is used for engine adjustment.
Connecting the following terminals of the TDCL to terminal E1 se-
lects the diagnosis mode shown.
NOTICE: Never make a mistake with the terminal connection
position as this will cause a malfunction.
TerminalSystem
TE1Engine and ECT (Normal mode)
TE2 and TE1Engine and ECT (Test mode)
TcABS, A/C, Airbag, Traction Control and Cruise
Control System
TTECT
Refer to the respective system for the inspection method.
HINT: By connecting the TDCL up to a monitor specifically de-
signed for use with the TDCL, the diagnosis result for each system
can be read easily.
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PRECAUTIONS FOR VEHICLES
EQUIPPED WITH TRACTION
CONTROL (TRAC) SYSTEM
When using a rear wheel two±wheel drum tester such as a
speedometer tester or chassis dynamometer, etc., or jacking up
the rear wheels and driving the wheels, always push in the TRAC
cut (ºTRAC OFFº) switch and turn the TRAC system OFF.
CONFIRM TRAC SYSTEM IS OFF
1. Press the TRAC cut (ºTRAC OFFº) switch.
2. Check that the TRAC OFF indicator light comes on when the
TRAC system is turned off by the TRAC cut switch.
HINT: The TRAC indicator light should always operate right after
the engine is restarted.
3. Begin measurements.
4. Press the TRAC cut switch again to change the TRAC to operative and check that the TRAC OFF indicator light goes
off.
HINT: The TRAC indicator light blinks when the TRAC system is
operative.
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INTRODUCTION Precautions for V
ehicles Equipped with Traction Cotnrol
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[1] CUSTOMER PROBLEM ANALYSIS
In troubleshooting, the problem symptoms must be confirmed accurately and \
all preconceptions must be
cleared away in order to give an accurate judgment. To ascertain just what the problem symptoms are, it is ex-
tremely important to ask the customer about the problem and the conditions at t\
he time it occurred.
Important Points in the Problem Analysis
The following 5 items are important points in the problem analysis. Past pr\
oblems which are thought to be unre-
lated and the repair history, etc. may also help in some cases, so as much information as possible s\
hould be
gathered and its relationship with the problem symptoms should be correctly asce\
rtained for reference in trou-
bleshooting. A customer problem analysis table is provided in the troubl\
eshooting section for each system for
your use.
Important Points in the Customer Problem Analysis
wWhat Vehicle model, system name
w When Date, time, occurrence frequency
w Where Road conditions
w Under what conditions? Running conditions, driving con\
ditions, weather conditions
w How did it happen? Problem symptoms
(Sample) Engine control system check sheet.
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[2] SYMPTOM CONFIRMATION AND DIAGNOSTIC CODE CHECK
The diagnostic system in the LEXUS SC400 fulfills various functions. The fi\
rst function is the Diagnostic Code
Check in which a malfunction in the signal circuits to the ECU is stored\
in code in the ECU memory at the time
of occurrence, to be output by the technician during troubleshooting. Anot\
her function is the Input Signal Check
which checks if the signals from various switches are sent to the ECU correct\
ly.
The air conditioner system has an Actuator Check function whereby the ECU a\
utomatically operates the actua-
tors of the damper and blowermotor, etc. to check the operation. The cruise control system has a Cancel Si\
gnal
Check function which memorizes and displays what sort of signal it was that l\
ast cancelled the cruise control.
By using these check functions, the problem areas can be narrowed down qui\
ckly and troubleshooting can be
performed effectively. Diagnostic functions are incorporated in the following systems in the \
LEXUS SC400.
SystemDiagnostic CodeCheckInput Signal Check(Sensor Check)Other Diagnosis Function
Engine (with Test Mode)
Automatic Transmission (with Test Mode)
Anti±Lock Brake
Traction Control (Option)
SRS Airbag
Power Seat (only vehicles with memory function)
Wireless Door Lock Control
Cruise Control Cancel Signal
Check
Air Conditioner Actuator Check
In diagnostic code check, it is very important to determine whether the pr\
oblem indicated by the diagnostic code
is still occurring or occurred in the past but returned to normal at pre\
sent. In addition, it must be checked in the
problem sym ptom check whether the malfunction indicated by the diagnostic code is d\
irectly related to the prob-
lem symptom or not. For this reason, the diagnostic codes should be chec\
ked before and after the symptom
confirmation to determine the current conditions, as shown in the table below. If this is not done, it may, depend-
ing on the case, result in unnecessary troubleshooting for normally oper\
ating systems, thus making it more diffi-
cult to locate the problem, or in repairs not pertinent to the problem. Ther\
efore, always follow the procedure in
correct order and perform the diagnostic code check.
DIAGNOSTIC CODE CHECK PROCEDURE
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[3] SYMPTOM SIMULATION
The most difficult case in troubleshooting is when there are no problem symptoms occurring. In s\
uch cases, a
thorough customer problem analysis must be carried out, then simulate the same or similar conditions and envi-
ronment in which the problem occurred in the customer's vehicle. No matter now much experience a technician
has, or how skilled he may be, if he proceeds to troubleshoot without confir\
ming the problem symptoms he will
tend to overlook something important in the repair operation and make a wron\
g guess somewhere, which will
only lead to a standstill. For example, for a problem which only occurs when\
the engine is cold, or for a problem
which occurs due to vibration caused by the road during driving, etc., the pr\
oblem can never be determined so
long as the symptoms are confirmed with the engine hot condition or the \
vehicle at a standstill. Since vibration,
heat or water penetration (moisture) are likely causes for problems which are \
difficult to reproduce, the symptom
simulation tests introduced here are effective measures in that the external causes are applied to the vehicle
in a stopped condition.
Important Points in the Symptom Simulation Test
In the symptom simulation test, the problem symptoms should of course be co\
nfirmed, but the problem area
or parts must also be found out. To do this, narrow down the possible problem circuits according to the sym\
ptoms
before starting this test and connect a tester beforehand. After that, carry out the symptom simulation test, judg-
ing whether the circuit being tested is defective or normal and also confir\
ming the problem symptoms at the
same time. Refer to the matrix chart of problem symptoms for each system to \
narrow down the possible causes
of the symptom.
[1] VIBRATION METHOD: When vibration seems to be the major cause.
CONNECTORS
Slightly shake the connector vertically and horizon-
tally.
WIRE HARNESS
Slightly shake the wire harness vertically and horizontally.
The connector joint, fulcrum of the vibration, and body
through portion are the major areas to be checked thor-
oughly.
PARTS AND SENSORS
Apply slight vibration with a finger to the part of the
sensor considered to be the problem cause and
check if the malfunction occurs.
HINT: Applying strong vibration to relays may result
in open relays. IN±20
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[2] HEAT METHOD: When the problem seems to occur when the suspect area is heated.
Heat the component that is the likely cause of the malfunc-
tion with a hair dryer or similar object. Check to see if the
malfunction occurs.
NOTICE:
(1) Do not heat to more than 60°C (140 °F).
(Temperature limit that no damage is done to the
component).
(2) Do not apply heat directly to parts in the ECU.
[3] WATER SPRINKLING METHOD: When the malfunction seems to occur on a
rainy\
day or in a high±humidity condition.
Sprinkle w ater onto the vehicle and check to see if the mal-
function occurs.
NOTICE:
(1) Never sprinkle water directly into the engine compartment, but indirectly change the tempera-
ture and humidity by applying water spray onto
the radiator front surface.
(2) Never apply water directly onto the electronic components.
(Service hint)
If a vehicle is subject to water leakage, the leaked water
may contaminate the ECU. When testing a vehicle with a
water leakage problem, special caution must be used.
[4] OTHER: When the malfunction seems to occur when electrical load is excessive.
Turn on all electrical loads including the heater blower,
head lights, rear window defogger, etc. and check to see
if the malfunction occurs.
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