1991 LEXUS SC400 engine

MECHANICAL SYSTEM TESTS
AT0QT±01
STALL TESTThe object of this test is to check the overall performance of the trans\
mission and engine by measuring
the stall speeds in the D and R positions.
NOTICE:
 Perform the test at normal operating fluid temperature 50±80 C (122±176 F).
 Do not continuously run this test longer than 5 seconds.
 To ensure safety, conduct this test in a wide, clear, level area, which provides good traction.
 The stall test should always be carried out in pairs. One technician sho\
uld observe the conditions of
wheels or wheel stoppers outside the vehicle while the other is performi\
ng the test.
MEASURE STALL SPEED
(a) Chock the 4 wheels.
(b) Connect a tachometer to the engine.
(c) Fully apply the parking brake.
(d) Keep your left foot pressed firmly on the brake pedal.
(e) Start the engine.
(f) Shift into the D position. Step all the way down on the accelerator peda\
l with your right foot.
Quickly read the stall speed at this time.
Stall speed:
2,200 + 150 RPM
(g) Perform the same test in R position.
AT±50±
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EVALUATION
 

Problem\
 
\

\
Possible cause 


\
 
\

\

Engine output may be insufficient.
 \
 \
 Stator one±way clutch is operating properly
 (a) Stall speed low in D and R positions.\
 \
HINT:
 \
 \
If more than 600 RPM below the specified value, the
 \
 \
torque converter could be faulty.
 \
 \
 Line pressure too low
 
(b) Stall speed high in Dposition
\
 \
 Forward clutch slopping 

(b) Stall speed high in D position.\
 
\
 No.2 one±way clutch not operating properly 


\
 
\

\

O/D one±way clutch not operating properly
 \
 \
 Line pressure too low
 (c) Stall speed high in Rposition\
 \
 Direct clutch slipping
 (c) Stall speed high in R position.\
 \
 First and reverse brake slipping
 \
 \
 O/D one±way clutch not operating properly
 \
 \
 Line pressure too low
 (d) Stall speed high in D and R position.\
 \
 Improper fluid level 

\
 
\
 O/D one±way clutch not operating properly
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TIME LAG TEST
When the shift lever is shifted while the engine is idling, there will be a \
certain time lapse or lag before the
shock can be felt. This is used for checking the condition of the O/D direct \
clutch, forward clutch, direct
clutch, and first and reverse brake.
NOTICE:
Perform the test at normal operating fluid temperature 50±80 C (122±176 F).
 Be sure to allow a one minute interval between tests.
 Make 3 measurements and take the average value.
MEASURE TIME LAG
(a) Fully apply the parking brake
(b) Start the engine and check idle speed.
Idle speed:
650 RPM (In N position and air conditioner OFF)
(c) Shift the shift lever from N to D position. Using a stop watch, measure the time it take\
s from shifting thelever until the shock is felt.
In same manner, measure the time lag for N
R.
Time lag:
N D Less than 1.2 seconds
N R Less than 1.5 seconds
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MEASURE LINE PRESSURE
NOTICE:
Perform the test at normal operating fluid temperature 50±80 C (122±176 F).
 The line pressure test should always be carried out in pairs. One technicia\
n should observe the
conditions of wheels or wheel stoppers outside the vehicle while the other is perf\
orming the test.
 Be careful to prevent the oil pressure gauge hose from interfering with \
the exhaust pipe.
(a) Warm up the transmission fluid.
(b) Remove the test plug on the transmission case left side and connect the \
oil pressure gauge SST.
SST 09992±00094
HINT: Connecting the oil pressure gauge will be made easier by moving LH sid\
e heat insulator aside.
(c) Fully apply the parking brake and chock the 4 wheels.
(d) Start the engine and check idling RPM.
(e) Keep your left foot pressed firmly on the brake pedal and shift into D p\
osition.
(f) Measure the line pressure when the engine is idling.
(g) Press the accelerator pedal all the way down. Quickly read the highest line pressure when engine speedreaches stall speed.
(h) In the same manner, perform the test in R position. AT±54
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(f) Fully apply the parking brake and chock the 4 wheels.
(g) Start the engine and check idling RPM.
(h) Keep your left foot pressed firmly on the brake pedal and shift into D p\
osition.
(i) Measure the accumulator back pressure.
(j) With the conditions the same as in (h), ground the other probe of the test\
lead which has one end insertedinto the terminal SLN of the ECM harness side connector, then measure the accumulator back pressure
again.
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LOCATION OF CONNECTORS
AT0LA±02
Location of Connectors in Engine Compartment
AT±72±
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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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This sensor detects the rotation speed of the O/D input shaft from the
rotation of the O/D direct clutch drum.
Its construction is the same as that of the No. 2 vehicle speed sensor
(See page AT±86).
By comparing the O/D direct clutch speed signal and the No. 2 vehicle
speed sensor signal, ECM detects the shift timing of the gears and ap-
propriately controls the engine torque and hydraulic pressure in re-
sponse to various conditions, thus performing smooth gear shift.
DTC67O/D Direct Clutch Speed Sensor Circuit
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
67
All conditions below are detected for 4 secs. or more
2 trip detection logic*
(a) Gear position: 1st, 2nd and 3rd
(b) T/M input shaft rpm: 100 rmp or more
(c) T/M output shaft rpm: less than 300 rpm
(d) PNP: OFF (other than P or N position)

O/D direct clutch speed sensor.

Harness or connector between O/D direct
clutch speed sensor and ECM.

ECM
*: See page AT±62.
Reference

Wave form between terminals NCO
+ and NCO± during engine idling.
AT±98
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