LEXUS SC400 1991 Service Repair Manual

OKNG
OKNG
INSPECTION PROCEDURE
1Check operation of speedometer.
Drive the vehicle and check if the operation of the speedometer in the c\
ombination meter is normal.
The No. 1 vehicle speed sensor is operating normally if the speedometer dis\
play is normal.C
Hint
Check speedometer circuit. See combination meter
troubleshooting on BE section.
2Check voltage between terminal SPD of ECM connector and body ground.
C
OK
P3. Connect the check harness A to the ECM (See EG section.)
4. Shift the shift lever to N position.
5. Jack up one of the rear wheels.
6. Turn ignition switch ON.
Measure voltage between terminal SPD of ECM con-
nector and body ground when he rear wheel is turned
slowly.
Voltage is generated intermittently.
Check speedometer circuit. See combination meter
troubleshooting on BE section.
Proceed to next circuit inspection shown on ma-
trix chart (See page AT±66).
However, when diag. trouble code 42 is displayed,
check and replace ECM.
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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.
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AT±66
IN±33
WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
±
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OKNG
INSPECTION PROCEDURE
1Check No. 4 solenoid valve.
C
OK
P
C
OK
C
OK
C
OK
Check solenoid resistance
1. Jack up the Vehicle
2. Remove the oil pan.
3. Disconnect the connector
Measure resistance between terminals 1 and 2 of sole-
noid connector.
Resistance: 5.1 ± 5.5

Check solenoid operation
Connect positive  lead with an 8±10 W bulb to terminal
1 of solenoid connector and negative  lead to terminal
2, then check the movement of the valve.
Reference
Check the solenoid's operation
1. Prepare a variable power supply.
2. Connect positive lead of the variable power
supply to terminal 1 of solenoid connector and neg-
ative  lead to terminal 2.
3. Check the movement of the valve when the voltage is gradually increased. (A current greater than 1 A
should not be supplied.)
As the voltage is increased, the valve should move slow-
ly in the direction.
4. Check the movement of the valve when the voltage is cut off.
The valve should return in the direction.
Replace No. 4 solenoid valve.
Go to step
.
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OKNG
2Check harness and connector between battery and No. 4 solenoid valve, No. 4 solenoid valve\
and ECM (See page IN±33).
Repair or replace harness or connector.
Proceed to next circuit inspection shown on ma-
trix chart (See page AT±66). However, when diag.
trouble code 46 is display, check and replace ECM.
±
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DTC61No.2 Vehicle Speed Sensor Circuit
CIRCUIT DESCRIPTION
The No.2 speed sensor detects the rotation speed of the transmission output shaft and sends signals to the
ECM. The ECM determines the vehicle speed based on the these signals. An AC voltage i\
s generated in the
No.2 vehicle speed sensor coil as the rotor mounted on the output shaft rota\
tes, and this voltage is sent to the
ECM.
The gear shift point and lock±up timing are controlled by the ECM based \
on the signals from this vehicle speed
sensor and the throttle position sensor signal.
If the No.2 vehicle speed sensor malfunctions, the ECM uses input signals \
from the No.1 vehicle speed sensor
as a back±up signal.
DTC No.DTC Detecting ConditionTrouble Area
61
All conditions below are detected 500 times or more
continuously.
2 trip detection logic*
(a) No No.2 vehicle speed sensor signal in 4 No.1 ve-
hicle speed sensor signal pulses.
(b) Vehicle speed: 5.6 MPH (9 km/h) or more for
at least 4 secs.
(c) Park/neutral position switch:
OFF (Other than P or N position)

No. 2 vehicle speed sensor

Harness or connector between No.2 vehicle
speed sensor and ECM.

ECM
*: See page AT±62
Reference

Waveform between terminals SP2+ and SP2± when vehicle speed is approx.\
37 MPH (60km/h).
AT±86
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IN±33AT±66
WIRING DIAGRAM
DIAGNOSTIC CHARTDIAGNOSTIC CHART
±
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NGOK
OKNG
INSPECTION PROCEDURE
1Check resistance between terminals SP2+ and SP± of ECM connector.
C
OK
PConnect the check A to the ECM. (See EG section).
Check resistance between terminals SP
+ and SP2± of
ECM connector.
Resistance: 560 ± 680

Proceed to next circuit inspection shown on matrix chart
(See page AT±66).
2Check No.2 vehicle speed sensor.
C
OK
Hint
P
OK
C
Remove No.2 vehicle speed sensor from transmission.
(See page AT±17).
Measure resistance between terminals 1 and 2 of speed
sensor.
Resistance: 560 ± 680

Reference
Check the vehicle speed sensor's function
Check voltage between terminals 1 and 2 of the vehicle
speed sensor when a magnet is put close to the front
end of the vehicle speed sensor then taken away quick-
ly.
Voltage is generated intermittently.
The voltage generated is extremely low.
Replace No.2 vehicle speed sensor.
Check and repair harness and connector between
ECM and No.2 vehicle speed sensor (See page
IN±33).
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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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