Lexus SC300 / Lexus SC400. Service manual — part 88

OK

NG

OK

NG

OK

NG

INSPECTION PROCEDURE

1

Check 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).

2

Check stop light signal.

C

OK

1.

Connect voltmeter to the terminals T

T

and E

1

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).

3

Check 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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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING

AT–109

AT–66

IN–33

WIRING DIAGRAM

Pattern Select Switch Circuit

CIRCUIT DESCRIPTION

The ECM memory contains the shift programs for the NORMAL and POWER patterns, 2 position and L
position and the lock–up patterns. Following the programs corresponding to the signals from the pattern
select switch, the park/neutral position switch and other various sensors the ECM switches the solenoid
valves ON and OFF, thereby controlling the transmission gear change and the lock–up clutch operation.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

AT–110

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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING

OK

NG

OK

NG

OK

NG

INSPECTION PROCEDURE

1

Check voltage between terminal P of ECM connector and body ground.

C

OK

Hint

P

1.

Connect the check harness A to the ECM (See EG
section).

2.

Turn ignition switch ON.

Measure voltage between terminal P of ECM connector
and body ground when the pattern select switch is set
to the PWR (POWER) position and NORM (NORMAL)
position.

The ECM uses the normal pattern signal if the power
signal is not input.

Proceed to next circuit inspection shown on matrix chart
(See page AT–66).

2

Check pattern select switch.

C

OK

P

Disconnect pattern select switch connector. (See BO
section).

Measure resistance between terminals 1 and 2 of pat-
tern select switch connector when the select switch is
set to PWR and NORM positions.

Replace pattern select switch.

3

Check harness and connector between ECM and pattern select switch, pattern select switch
and battery (See page IN–33).

Repair or replace harness or connector.

Check and replace ECM.

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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING

AT–111

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 malfunction is detected. In this
case, connecting the terminals in the DLC2 or DLC1 can display the malfunction code.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

See next page.

AT–112

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A304E (1UZ–FE) AUTOMATIC TRANSMISSION

TROUBLESHOOTING