Lexus SC300 / Lexus SC400. Manual - part 70

–Memo–

AT–36

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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING

DIAGNOSIS SYSTEM

AT09R–07

The electronically controlled transmission system has built–
in self–diagnostic functions. If the malfunction occurs in the
system, the ECM stores the malfunction code in memory and
the O/D OFF (Overdrive OFF) indicator light blinks to inform
the driver. The diagnostic trouble code stored in memory can
be read out by the following procedure.

O/D OFF INDICATOR LIGHT INSPECTION

AT09S–07

1. 

Turn the ignition switch to ON.

2. 

Check if the O/D OFF indicator light lights up when the
O/D main switch is pushed out to OFF and goes off when
the O/D main switch is pushed in to ON.
HINT:

•

If the O/D OFF indicator light does not light up or stay on
all the time, carry out the check for “O/D OFF Indicator
Light Circuit” on page AT–112.

•

If the O/D OFF indicator light blinks, a trouble code is
stored in the ECM memory.

DIAGNOSTIC TROUBLE CODE CHECK

AT0A3–07

1. 

Turn the ignition switch ON, but do not start the engine.

2. 

Push in the O/D main switch to ON.
HINT: Warning and diagnostic trouble codes can be read only
when the O/D main switch is ON. If it is OFF, the O/D OFF indi-
cator lights up continuously and will not blink.

3. 

Using SST, connect terminals TE1 and E1 of the DLC2 or
DLC1.
SST 09843–18020

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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING

AT–37

4. 

Read the diagnostic trouble code indicated by the
number 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 “42” 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 

the

prompts 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

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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING

CHECK TERMINAL T

T

 OUTPUT

VOLTAGE

AT00R–01

When a voltmeter is connected to the DLC1, the following
items can be checked.
1. 

Throttle position sensor signal

2. Brake 

signal

3. Shift 

position 

signal

1. VOLTMETER 

CONNECTION

Connect the positive (+) probe of the voltmeter to terminal T

T

and the negative (–) probe to terminal E1 of the DLC2.
HINT: If a voltmeter with small internal resistance is used, the
correct voltage will not be indicated, so use a voltmeter with
an internal resistance of at least 10 k

.

2. 

TURN IGNITION SWITCH TO ON (DO NOT START THE
ENGINE)

3. 

CHECK THROTTLE POSITION SENSOR SIGNAL
Check if the voltage changes from approximately 0 V to
approximately 8 V when the accelerator pedal is gradually
depressed from the fully closed position.

4. 

CHECK BRAKE SIGNAL (LOCK–UP CUT SIGNAL)

(a)  Open the throttle valve fully to apply approximately 8 V to

terminal T

T

.

(b)  In this condition, check terminal T

T 

voltage when the brake

pedal is depressed and released.

T

T

 terminal voltage:

0 V (When brake pedal is depressed)

8 V (When brake pedal is released)

5. START 

ENGINE

6. 

CHECK SHIFT POSITION SIGNAL
(VEHICLE SPEED ABOVE 60 KM/H OR 37 MPH)
Check up–shifting together with terminal T

T

 voltage.

HINT: Check for light shocks from up–shifting and for
changes in the tachometer.

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Gear Position

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Terminal T

T

 output voltage

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1st Gear

Below 0.5 V

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2nd Gear

1.5 

~ 

2

 

6 V

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3rd Gear

3.5 

~ 

4.6 V

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3rd Lock–up

4.5 

~ 

5.9 V

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O/D

5.5 

~ 

6.9 V

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O/D Lock–up

6.5 

~

 7.9 V

If terminal T

T

 output voltage check cannot be performed, per-

form the check of terminal T

T

 circuit on page AT–120.

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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING

AT–39