cruise control LEXUS SC300 1991 Service Repair Manual

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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INTRODUCTION Total Diagnostic Communication Link (TDCL)IN±7
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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.
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INTRODUCTION How to Troubleshoot ECU Controlled SystemsIN±15
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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
IN±18±
INTRODUCTION How to Troubleshoot ECU Controlled Systems
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PROBLEM SYMPTOM CONFIRMATION
AT09U±07
Taking into consideration the results of the customer problem analysis, try to\
reproduce the symptoms of
the trouble. If the problem is that the transmission does not up±shift, \
does not down±shift, or the shift point
is too high or too low, conduct the following road test referring to the automatic shift schedu\
le and simulate
the problem symptoms.
ROAD TEST
AT09V±05NOTICE: Perform the test at normal ATF operating temperature
50±80 5C (122±176 5F).
1. D POSITION TEST (NORM AND PWR PATTERN)
Shift into the D position and fully depress the accelerator ped-
al and check the following points:
(a) Check up±shift operation
1" 2, 2 "3 and 3 "O/D up±shift takes place, and shift point
should conform to those shown in the automatic shift sched-
ule (See page AT±45)
Conduct a test under both Normal and Power patterns.
HINT:
w O/D up±shift or lock±up will not occur when the engine
coolant temp. is below 60
C (140
F) and speed is under
60 km/h (37 mph), or if there is a 10 km/h (6 mph)
difference between the set cruise control speed.
w 3rd up±shift or lock±up will not occur when engine
coolant temp. is below 35
C (95
F) and speed is under
40 km/h (25 mph).
(b) Check for shift shock and slip. In the same manner, check the shock and slip at the 1 "2,
2 " 3 and 3 "O/D up±shifts.
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A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTINGAT±41
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PWR Mode (Kick±down foot switch deactivated)
Shift positionShifting pointVehicle speed km/h (mph)  Throttle valve fully opened 1"2 67±71 (42±44)  2"3 118±124 (73±77)  3"O/D 179±186 (111±116) 
Dposition
 O/D"3 149±155 (93±96) D position 3"2 95±100 (59±62)  2"1 22±26 (14±16)  Throttle valve fully closed 3"O/D 32±35 (20±22)  O/D"3 23±26 (14±16)  Throttle valve fully opened 1"2 67±71 (42±44) 
2 position
 3"2 106±112 (66±70)  2"1 10±13 (6±8) 
Lposition
 Throttle valve fully opened 3"2 104±109 (65±68) L position 2"1 57±63 (35±39)
LOCK±UP POINT
NORM Mode
 D position km/h (mph) 
Lock±upON
 
Lock±upOFF Throttle valve opening 5% Lock±up ON Lock±up OFF
 *3rd Gear 83±88 (52±55) 77±82 (48±51)
 O/D Gear 56±60 (35±37) 53±57 (33±35)
*: O/D Switch OFF
PWR Mode
D position km/h (mph)Lock±upONLock±upOFF Throttle valve opening 5%Lock±up ONLock±up OFF
 *3rd Gear 83±88 (52±55) 77±82 (48±51)
 O/D Gear 56±60 (35±37) 53±57 (33±35)
*: O/D Switch OFF
HINT:
(1) There is no lock±up in the 2 and L positions.
(2) In the following cases, the lock±up will be released regardless\
of the lock±up pattern.

When the throttle valve is completely closed.

When the brake light switch is ON.
(3) Shift up to 3rd will not occur when the engine coolant temp. is below 3\
5 C (95 F) and the vehicle speed
is below 40 km/h (25 mph).
(4) Shift±up to O/D will not occur when the engine coolant temp. is\
below 60 C (140 F) and the vehicle
speed is below 63 km/h (39 mph).
(5) During cruise control operation, the shift pattern is fixed in NOR\
M. And when the vehicle speed drops to 10 km/h (6 mph) or more below the cruise control set vehicle speed, s\
hift down from O/D to 3rd
occurs.
(6) The kick±down foot switch turns ON when the accelerator pedal i\
s depressed further with the throttle valve already fully open.
AT±46
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A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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AT±66
IN±33
WIRING DIAGRAM
O/D Cancel Signal Circuit
CIRCUIT DESCRIPTION
While driving with cruise control activated, in order to minimize gear shifti\
ng and provide smooth cruising
when driving uphill, overdrive may be prohibited temporarily in some conditions.The cruise control ECU
sends O/D cut signals to the ECM as necessary and the ECM cancels overdrive s\
hifting until these signals
are discontinued.(For details, see the cruise control system, on BE sectio\
n).
DIAGNOSTIC CHARTDIAGNOSTIC CHART
AT±116±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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NGOK
NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal OD1of ECM connector and body ground.
C
OK
P1. Connect the check harness A to the ECM (See EGsection).
2. Turn ignition switch ON.
Measure voltage between terminal OD1 of ECM con-
nector and body ground.
Voltage: 4 ± 6 V
Proceed to next circuit inspection shown on matrix chart
(See page AT±66).
2Check voltage between terminal OD of cruise control ECU harness side con\
nector and body
ground.
C
OK
P1. Disconnect cruise control ECU connector.
2. Turn ignition switch ON.
Measure voltage between terminal OD of cruise control
ECU harness side connector and body ground.
Voltage: 4 ± 6± V
Check and replace cruise control ECU.
3Check harness or connector between cruise control ECU and ECM (See page\
IN±33).
Repair or replace harness or connector.
Check and replace ECM.
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A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTINGAT±117
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Description
The power source supplies power to each of the vehicle's electrical devices. It is composed of the battery, fuses
and relays, which are located centrally at relay block No. 2 and relay block No. 6 i\
n the engine compartment
and junction block No. 1 relay block No. 4 and relay block No. 5 in the \
cabin near the driver's feet.
Related systems for each Fuse
No.Part NameRelated Systems or Parts
1IGN
Charging System
AIR±BAG System1IGN
Engine
2ST
Starter
3WIPER
Wiper and Washer System
4HTR
Defogger System
A/C System
5ENGINE
Charging System
6RADIO NO. 2
Audio System
Power Mirror System

Cigarette Lighter
A/C System
7CIG
Combination Meter System
AIR±BAG System7CIG
Shift Lock System
Theft Deterrent System

TEL System
8STOP
Stop Light System
Cruise Control System
9TURN
Turn Signal and Hazard
Warning Light System
Cornnering Light System
10MIR HTR
Mirror Heater System
11PANEL
Illumination Light System
12ECU±B
Combination Meter System
AIR±BAG System

Combination Meter System
ECT System
13GAUGE
Back±Up Light
Transmission Indicator

Light Failare Sensor
ABS and TRAC

Power Seat System
Door Lock Control System

TEL System
Shift Lock System
14ECU±IG
Radiator Fan
Auto Antenna

Electric Tension Reducer System
Power Steering

Auto±Tilt away Steering
Cruise Control System
15TAIL
Taillight System
Side Marker15TAIL
Clearance Light
16DOOR
Power Seat System
Luggage Door Opener16DOOR
Door Lock Control System
Fuel Lid Opener System
17IG SWUpstream of ECU±IG, ENGINE, WIP, HTR, TURN, GAUGE, and ST Fuse
18PWR
Power Window System
Sliding Roof System
19ABS NO. 1
ABS and TRAC
20AM1Upstream of MIR HTR, TAIL, PANEL, STOP, ECUA±B, DOOR and PWR Fuse
21ALTUpstream of DEF, HTR, AM1, and ABS No. 1 Fuse
BE±18±
BODY ELECTRICAL SYSTEM Power Source
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No.Part NameRelated Systems or Parts
22MAIN
Upstream of ALT±S and EFI Fuse
23AM2
Charging System
Engine23AM2
AIR±BAG System
24ABS NO. 2
ABS and TRAC
25INJ
Charging System
Engine25INJ
AIR±BAG System
26DEF
Defogger System

Power Seat System
Sliding Roof System

A/C System
Liquid Crystal Inner Mirror System
27DOME
Combination Meter System
Interior Light System27DOME
ABS and TRAC
Wireless Door Lock Control System

Cruise Control System
Auto±Tilt away Steering

Theft Deterrent System
28EFI
Engine
29HAZ HORN
Turn Signal and Hazard Warning Light System29HAZ±HORN
Horn System
30RADIO NO. 1
Audio System
31TEL
TEL System
32ALT±S
Charging System
33TRAC
ABS and TRAC
34HEAD (RH±LWR)
Headlight System
35HEAD (LH±LWR)
Headlight System
36HEAD (RH±UPR)
Headlight System
37HEAD (LH±UPR)
Headlight System
38HTR
Blow Motor
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BODY ELECTRICAL SYSTEM Power SourceBE±19
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Shift Lock ECU
Tilt and Power
Telescopic ECU
Airbag ECU
Cruise Control ECU Engine ECUABS and Traction ECU
(w/ Traction System) or
ABS ECU
(w/o Traction System)
Theft Deterrent and
Door Lock ECU
(w/ Traction System)
Traction ECU
Remote Control Mirror ECU A/C Control Amplifier
PPS ECU
Engine Cooling Fan ECU
Component to be aligned
Section of repair manual
for relevant model year
Front Wheels Suspension and Axle (SA) section
Rear Wheels Suspension and Axle (SA) section
Propeller Shaft Propeller Shaft (PR) section
2. BRAKE SYSTEM
The brake system is one of the most important safety components. Always \
follow the directions and
notes given in section BR of the repair manual for the relevant model ye\
ar when handling brake sys-
tem parts.
NOTICE: When repairing the brake master cylinder or TRAC system, bleed t\
he air out of the TRAC
system.
3. DRIVE TRAIN AND CHASSIS
The drive train and chassis are components that can have great effects on the running performance
and vibration resistance of the vehicle. After installing components in \
the sections listed in the table
below, perform alignments to ensure correct mounting angles and dimensions. P\
articularly accurate
repair of the body must also be done to ensure correct alignment.
HINT: Correct procedures and special tools are required for alignment. Alway\
s follow the directionsgiven in the repair manual for the relevant model year during alignment \
and section DI of this manual.
4. ECU (ELECTRONIC CONTROL UNIT)
Locations of ECUs
INTRODUCTIONIN-8
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