LEXUS SC400 1991 Service Repair Manual

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.
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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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EVALUATION
If N " D or N " R time lag are longer than specified:
 Problem\
 \
Possible cause 






N " D time lag is longer
\
 
\


\


\

\


Line pressure too low
 Forward clutch worn
 O/D one±way clutch not operating properly
 Accumulator back pressure too low
 






N " R time lag is longer
\
 
\


\


\

\


Line pressure too low
 Direct clutch worn
 First and reverse brake worn
 O/D one±way clutch not operating properly
 Accumulator back pressure too low
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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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SPECIFIED LINE PRESSURE
 
Condition
 
D positionkPa (kgf/cm2, psi)
 
R positionkPa (kgf/cm2, psi) 

Idling
 

382±441 (3.9±4.5, 55±64)
 

637±716 (6.5±7.3, 92±104) 

Stall
 

1,265±1,402 (12.9±14.3, 183±203)
 

1,726±2,060 (17.6±21.0, 250±299)
If the measured pressures are not up to specified values, recheck the thro\
ttle cable adjustment and perform
a retest.
EVALUATION
 Problem\
 \
Possible cause
 \
 \

Throttle cable out of adjustment If the measured values at all positions are higher.\
 \
 Throttle valve defective 


\

\

\

Regulator valve defective
 \
 \
 Throttle cable out of adjustment
 \
 \
 Throttle valve defective
 If the measured values at all positions are lower.\
 \
 Regulator valve defective
 \
 \
 Oil pump defective
 \
 \
 O/D direct clutch defective
 
Ifpressure is low in the Dposition only
\
 \
 D position circuit fluid leakage If pressure is low in the D position only.\
 \
 Forward clutch defective 


\

\

\

R position circuit fluid leakage
 If pressure is low in the R position only.\
 \
 Direct clutch defective
 \
 \
 First and reverse brake defective
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MEASURE ACCUMULATOR BACK PRESSURE
AT0QU±01
NOTICE:
Perform the test at normal operating fluid temperature 50±80 C (122±176 F).
 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 rear right side and connec\
t the oil pressure gauge SST.
SST 09992±00094
HINT: Connecting the oil pressure gauge will be made easier by moving the RH \
side head insulator aside.
(c) Remove the passenger side No.2 under cover and ECM protector.
(d) Connect the SST (check harness A) between ECM and connector of vehicle\
wire harness.
SST: 09990±01000
(e) Install one test lead probe into the terminal SLN of the ECM wire harnes\
s side connector and take care not to ground the other test lead probe.
HINT: Prepare test leads which are connected with an (approximately) 8 W l\
ight bulb.
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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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SPECIFIED ACCUMULATOR BACK PRESSURE
 Condition if ECM terminal SLN Not ground kPa (kgf/cm2, psi) Ground kPa (kgf/cm2 , psi) 

Accumulator back pressure 

177±255 (1.8±2.6, 26±37) 

0
EVALUATION
 Problem\
 \
Possible cause \
 \

Throttle cable out of adjustment 

Th l t b k i t ifi d
\

\

\

Throttle valve defective
 The accumulator back pressure is not as specified
(high or low) when the terminal SLN is not ground.\
 \
 Solenoid modulator valve defective
 
(high or low) when the terminal SLN is not ground.
\
 \
 SLN solenoid valve defective
 \
 \
 Accumulator control valve defective
 


The accumulator back pressure does not become 0
kgf/cm2 when the terminal SLN is grounded.
\

\

\

SLN solenoid valve defective
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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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