light LEXUS SC400 1991 Service Workshop Manual

*1: ªOº mark means ªO/D OFFº light blinks once every 2 seconds.\
ªXº mark means ªO/D OFFº light never
blinks.
*2: ªOº mark means the ECM memorizes the malfunction code if the ECM detects the diag. trouble \
code
detection condition.
*3: This indicates items for which ª2 trip detection logicº is use\
d. With this logic, when a logic malfunction
is first detected, the malfunction is temporarily stored in the ECM memory. If the same case is detected
again during the second drive test, this second detection causes the O/F\
OFF Light to blink.
The 2 trip repeats the same mode twice. (However, the IG switch must be turned OFF between the 1st trip
and 2nd trip.)
HINT:

If the malfunction returns to normal while a malfunction warning is being \
output, the O/D OFF indicator
light stops blinking and goes off.
However, the malfunction code is retained in memory until it is cleared from me\
mory.

If the diagnosis system outputs a malfunction code even though the O/D OFF indicator was not
blinking, there is intermittent trouble. Check all the connections in the circuit\
s corresponding to that
code.

If the vehicle speed sensors No.1 and No.2 happen to fail simultaneously\
, the ECM will neither alert
the driver by blinking the O/D OFF indicator nor record any diagnostic t\
rouble code. It will, however,
decide that the vehicle can be driven only in 1st and none of the other gears, shifting \
upwards will then
be prohibited.

Codes 46, 62, 63 and 64 are limited to short or open circuits in the electric\
al system comprised of the
solenoids, wire harnesses and connectors. The ECM is unable to detect mechanical t\
rouble (sticking,
for example) in the solenoid valves.
AT±62
±
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DTC46No. 4 Solenoid Valve Circuit (For Accumula-
tor Back Pressure Modulation)
CIRCUIT DESCRIPTION
The No. 4 solenoid valve controls the hydraulic pressure acting on the
brakes and clutches of the planetary gear units when gears are shifted and
performs smooth gear shifting.
The ECM determines optimum operating pressure according to the signals
from the throttle position sensor, vehicle speed sensor and O/D clutch
speed sensor and controls the volume of current flow to the solenoid valve.
The amount of electric current to the solenoid is controlled by the (*) \
duty
ratio of ECM out put signals, causing momentary change to the hydraulic
pressure acting on the clutches during gear shifting.
When the duty ratio is high, the hydraulic pressure acting on the clutch\
es
is low.
(*) Duty Ratio
The duty ration is the ration of the period of continuity in one cycle. For\
example, if A is the period of continuity
in one cycle, and B is the period of non±continuity, then
DTC No.DTC Detecting ConditionTrouble Area
46
All conditions below are detected for 1 sec. or more.
2trip detection logic*
(a) ECM outputs duty signal to No. 4 solenoid in 90%
or higher duty ratio.
(b) Current to No. 4 solenoid:330
100 Ma OR LESS
(O/D OFF indicator light doesn't blink)
 No. 4 solenoid valve.
 Harness or connector between No. 4 sole-
noid valve and ECM
 ECM
*: See page AT±62.
Reference Reference
 Waveform between terminals SLN± and E
1when engine is idling. 
Waveform between terminals SLN± and E1 during shift
change.
AT±82±
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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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DTC64No. 3 Solenoid Valve Circuit
(For Lock±up Control Pressure Modulation)
CIRCUIT DESCRIPTION
The No. 3 solenoid valve is provided for lock±up operations.
The lock±up operation pressure is controlled by the linear sole-
noid for smooth engagement.
The amount of current flow to the solenoid is controlled by the
duty ratio (See page AT±82) of ECM output signal. The higher
the duty ration becomes, the higher the lock±up hydraulic pres-
sure becomes during the lock±up operation. If the malfunction
occurs in this circuit and diagnostic trouble code 64 is stored in
memory, the O/D OFF indicator light does not blink.
DTC No.DTC Detecting ConditionTrouble Area
64
All conditions below are detected for 1 sec. or more.
2 trip detection logic*
(a) ECM outputs duty signal to No. 3 solenoid in 90%
or higher duty ration.
(b) Current to No. 3 solenoid: 450
100 mA or less.
 No. 3 solenoid valve
 Harness or connector between No. 3 sole-
noid valve and ECM.
 ECM
*: See page AT±62
Reference
 Waveform between terminals SLU± and E
1 when lock±up function is not operated.
Reference
 Waveform between terminals SLU± and E
1 when lock±up function is operated.
AT±94±
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OKNG
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal R, PNP, 2, L of 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 terminals R, PNP, 2, L of
ECM connector and body ground when the shift lever is
moved to the following positions.
*: The voltage will drop slightly due to lighting up of the
back up light.
Proceed to next circuit inspection shown on matrix chart
(See page AT±66).
2Check park/neutral position switch.
C
P1. Jack up the vehicle.
2. Remove park/neutral position switch (See page AT±18).
Check continuity between each terminal shown below
when the shift lever is moved to each position.
Replace park/neutral position switch.
3Check harness and connector between ECM and park/neutral position switch, park\
/neutral
position switch and battery (See page IN±33).
Repair or replace harness and connector.
Check and replace ECM.
±
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AT±66BE
IN±33
WIRING DIAGRAM
Stop Light Switch Circuit
CIRCUIT DESCRIPTION
The purpose of this circuit is to prevent the engine from stalling, while d\
riving in lockup condition, when
brakes are suddenly applied.When the brake pedal is operated, this switch sends a signal to ECM. Then
the ECM cancels operation of the lockup clutch while braking is in progress\
.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
AT±108±
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OKNG
OKNG
OKNG
INSPECTION PROCEDURE
1Check operation of stop light.
Check if the stop lights go on and off normally when the brake pedal is operated and released.C
Check and repair stop light circuit (See BE section).
2Check stop light signal.
C
OK
1. Connect voltmeter to the terminals TT and E1 of the
DLC2.
2. Turn ignition switch ON (Do not start the engine).
3. Fully depress the accelerator pedal until the volt- meter indicates 8 V and hold it.
4. Depress and release the brake pedal and check the
voltage.
Proceed to next circuit inspection shown on matrix chart
(See page AT±66).
3Check harness and connector between ECM and stop light switch (See page\
IN±33).
Repair or replace harness or connector.
Check and replace ECM.
±
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WIRING DIAGRAM
O/D Main Switch and O/D OFF Indicator Light Circuit
CIRCUIT DESCRIPTION
The O/D main switch contacts go off when the switch is pushed in and comes on when it is pushed out.
In O/D main switch OFF position, the O/D OFF indicator lights up, and the \
ECM prohibits shifting to over-
drive. The ECM also causes the O/D OFF indicator light to blink when a malfunc\
tion is detected. In this
case, connecting the terminals in the DLC2 or DLC1 can display the malfu\
nction code.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
See next page.
AT±112
±
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O/D OFF indicator light does not light up.
AT±66
BE IN±33
IN±33
O/D OFF indicator light blinks
Perform diagnostic trouble code check (See page AT±38).
±
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OKNG
OKNG
OKNG
INSPECTION PROCEDURE
1Check operation of O/D Main Switch
C
OK
Hint
C
OK
1. Turn ignition switch ON.
2. Check ªO/D OFFº light when O/D main switch ispushed in to ON.
ªO/D OFFº light goes off.
3. Check ªO/D OFFº light when O/D main switch is pushed again, to OFF.
ªO/D OFFº light lights up.
If the ªO/D OFFº lights blinks when the O/D main switch
is pushed in to ON, a malfunction is occurring in the sys-
tem.
Check the diagnostic trouble code.
Go to step
.
2Check voltage between terminal OD2 of ECM connector and body ground.
C
OK
P1. Connect the check harness A to the ECM (See EG
section).
2. Turn ignition switch ON.
Check voltage between terminal OD2 of ECM and body
ground
Proceed to next circuit inspection shown on matrix chart
(See page AT±66).
3Check harness and connector between O/D off indicator light and ECM (Se\
e page IN±33).
Repair or replace harness or connector.
Check and replace ECM.
AT±114±
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