1991 LEXUS SC400 manual transmission

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
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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
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4. Read the diagnostic trouble code indicated by thenumber of times the O/D OFF indicator light blinks.
HINT: If the system is operating normally, the light will blink
2 times per second.
The malfunction code is indicated as shown in the illustration
at left (Diagnostic trouble code ª42º is shown as an example).
HINT: When 2 or more trouble codes are stored in memory,
the lower±numbered code is displayed first.
If no diagnostic trouble code is output, or if a diagnostic
trouble code is output even though no diagnostic trouble
code output operation is performed, check the TE1 terminal
circuit on page AT±118.
DIAGNOSTIC TROUBLE CODE CHECK
BY USING LEXUS HAND±HELD TESTER
AT0RD±01
1. Hook up the LEXUS hand±held tester to the DLC2.
2. Read the diagnostic trouble codes by following theprompts on the tester screen.
Please refer to the LEXUS hand±held tester operator's
manual for further details.
CANCELING DIAGNOSTIC TROUBLE
CODE
AT09T±07
After repair of the trouble area, the diagnostic trouble code
retained in the ECM memory must be canceled out by remov-
ing the EFI fuse for 10 seconds or more, with the ignition
switch off.
Check that the normal code is output after connecting the
fuse.
AT±38
±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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ECM DATA MONITOR BY USING LEXUS
HAND±HELD TESTER
AT0RE±01
1. Hook up the LEXUS hand±held tester to the DLC2.
2. Monitor the ECM data by following the prompts on thetester screen.
HINT: LEXUS hand±held tester has a ªSnapshotº function
which records the monitored data.
Please refer to the LEXUS hand±held tester operator's
manual for further details.
ECM TERMINAL VALUES
MEASUREMENT BY USING LEXUS
BRAKE±OUT BOX AND LEXUS
HAND±HELD TESTER
AT0RF±01
1. Hook up the LEXUS brake±out box and LEXUShand±held tester to the vehicle.
2. Read the ECM input/output values by following the
prompts on the tester screen.
HINT: LEXUS hand±held tester has a ªSnapshotº function.
This records the measured values and is effective in the diag-
nosis of intermittent problems.
Please refer to the LEXUS hand±held tester/LEXUS brake±
out box operator's manual for further details.
AT±40
±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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MANUAL SHIFTING TEST
AT0QV±01
HINT: With this test, it can be determined whether the trouble
is within the electrical circuit or is a mechanical problem in the
transmission.
1. DISCONNECT SOLENOID WIRE
2. INSPECT MANUAL DRIVING OPERATION Check that the shift and gear positions correspond with the
table below.
 Shift Position Gear Position
 D PositionO/D 2 Position3rd L Position1st 

R PositionReverse
 P PositionPawl Lock
HINT: If the L, 2 and D position gear positions are difficult to
distinguish, perform the following road test.
w
While driving, shift through the L, 2 and D positions.
Check that the gear change corresponds to the shift
position.
If any abnormality is found in the above test, the problem is
in the transmission itself.
3. CONNECT SOLENOID WIRE
4. CANCEL OUT DIAGNOSTIC TROUBLE CODE (See page AT±39)
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A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTINGAT±59
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Chapter 2. On±Vehicle Repair
( : '94 A340E and A341E AUTOMATIC TRANSMISSION Repair Manual for LEXUS SC400)
AT±48
AT±48
V04379
AT±68±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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Chapter 3. Off±Vehicle Repair
( : '94 A340E and A341E AUTOMATIC TRANSMISSION Repair Manual for LEXUS SC400)
AT±25
AT±70±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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DTC62, 63No. 1, No. 2 Solenoid Valve Circuit
CIRCUIT DESCRIPTION
Shifting from 1st to O/D is performed in combination with ON and OFF of the No. \
1 and No. 2 solenoid valves
controlled by ECM. If an open or short circuit occurs in either of the solenoid valves\
, the ECM controls the remain-
ing normal solenoid to allow the vehicle to be operated smoothly (Fail saf\
e function.
Fail Safe Function
If either of the solenoid valve circuits develops a short or an open, th\
e ECM turns the other solenoid ON and
OFF to shift to the gear positions shown in the table below. The ECM also turns the lock±up solenoid valve OFF
at the same time. If both solenoids malfunction, Hydraulic control cannot \
be performed electronically and must
be done manually.
Manual shifting as shown in the following table must be done. (In the case of \
a short circuit, the ECM stops send-
ing current to the short circuited solenoid).
 

Position
 

NORMAL
 

NO. 1 SOLENOID
MALFUNCTIONING 

NO. 2 SOLENOID
MALFUNCTIONING 

BOTH SOLENOIDS
MALFUNCTIONING
 Position Solenoid valve Gear Solenoid valve Gear Solenoid valve Gear Gear when shift selectoris
  No. 1 No. 2 Gear No. 1 No. 2 Gear No. 1 No. 2 Gear 
Gear when shift selectorismanually operated
  ON OFF 1st x ON 3rd ON x 1st O/D
 D ON ON 2nd x ON 3rd OFF x O/D O/D
  OFF ON 3rd x ON 3rd OFF x O/D O/D
  OFF OFF O/D x OFF O/D OFF x O/D O/D
  ON OFF 1st x ON 3rd ON x 1st 3rd
 2 (S) ON ON 2nd x ON 3rd OFF x 3rd 3rd

()
OFFON3rdxON3rdOFFx3rd3rd 
L
 ON OFF 1st x OFF 1st ON x 1st 1st L ON ON 2nd x ON 2nd ON x 1st 1st
x: Malfunctions
Check the No. 1 solenoid when diagnostic trouble code 62 is output and check t\
he No. 2 solenoid when diagnos-
tic trouble code 63 is output.
DTC No.DTC Detecting ConditionTrouble Area
62, 63

Solenoid resistance of 8
or less is detected (*)
8 times or more when solenoid is energized.

Solenoid resist ance of 100 k
or more is detected
(*) 8 times or more when solenoid is not energized.
Solenoid valve.

Harness or connector between solenoid and
ECM.

ECM
(*) If the above failures are detected less than 8 times, the ECM memo\
rizes the malfunction code but the O/D
OFF indicator light doesn't blink. AT±90
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A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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