Lexus SC300 / Lexus SC400. Service manual - part 193

PRECHECK TYPE I

In cases where the wireless door lock control system fails to operate only at a specific locality, perform this check
at that locality.

Open the driver’s door
(Other doors remain closed).

Using the door lock control switch, perform
“lock, unlock” 

*1

 operation 10 times within 30

seconds.

How many times in 10 seconds is “lock, un-
lock” 

*1

 operation performed automatically by

the ECU?

Noise is being produced at that locality. 

*3

Vehicle is now receiving signals from a
transmitter of another vehicle (during
transmission from transmitter of another
vehicle).

Malfunction on vehicle side
(Proceed to Matrix Chart of Problem
Symptom on page 

BE–454

).

Does not
operate

2 times

3 times

Normal 

*2

*1:

Performing lock and unlock once counts as one time.

*2:

If noise is not constantly produced at the locality being used and inspection is performed on an occasion
when there is no noise, then it may happen that the system is judged normal.

*3:

If the conclusion is that noise is produced in the locality the vehicle is used, then transmitter use is limited
in that locality. Limitations on usage are described below.

HINT:
Because the transmitter uses weak electromagnetic waves, it is easily affected by noise, so remote control with-
in the normal range becomes difficult.
To reduce the influence of noise, bring the transmitter as close as possible to the back window glass (antenna
section), or touch (ground) the grooved key tip of the transmitter to the door key cylinder and then operate the
transmitter switch; this should make door lock remote control operation possible.
If door lock remote control operation is still not possible, insert the key in the door key cylinder and press the
transmitter switch.

–

BODY ELECTRICAL SYSTEM

Wireless Door Lock Control System

BE–445

Open the driver’s door
(Other doors remain closed).

Using the door lock control switch, perform
“lock, unlock” 

*1

 operation 10 times with in

30 seconds.

Soon (less than 2 secs.) after performing
the above, continue to press the transmitter
switch for 10 seconds.

How many times does “lock, unlock” *1 op-
eration of all doors occur during the time the
transmitter is operated (approx. 10 secs.)?

Malfunction on vehicle side
(Proceed to Matrix Chart of Problem
Symptom on page 

BE–454

).

Wrong transmitter parts (exclusive code
does not match).
[Replace transmitter and ROM in ECU.
(See page 

BE–449

)]

Transmitter fault
(Inspect transmitter on page 

BE–447

).

Close all doors.

Tune the FM radio to 94.9 MHz.

Inspect transmitter (See page 

BE–447

).

Do all doors lock and unlock?

Is there noise on the radio while the trans-
mitter switch is being pushed? *2

Malfunction on antenna curcuit
(Inspect antenna circuit on page 

BE–448

).

Malfunction on vehicle side
(Proceed to Matrix Chart of Problem
Symptom on page 

BE–454

).

3 times

2 times

Does not
operate

YES

YES

NO

NO

Once

 

Disconnect the antenna cable from the ECU, directly insert
the transmitter (grooved section of key) and press the trans-
mitter switch. In this case do not let the transmitter come in
contact with the ECU case (because the transmitter will be
grounded).

PRECHECK TYPE II

Perform this check in cases where the wireless door lock control system fails to operate anywhere.

*1:

Performing lock and unlock once counts as one time.

*2:

In some localities, inspection cannot be carried out because the local FM radio broadcast is also at 94.9

MHz. When this occurs, perform inspection using a portable radio in a place indoors free from the influence

of FM broadcasts.

BE–446

–

BODY ELECTRICAL SYSTEM

Wireless Door Lock Control System

NG

OK

INSPECTION OF TRANSMITTER

HINT: Perform this inspection only when transmitter is judged to be the faulty in precheck type II.

1

Transmitter battery capacity check.

C

OK

P

Hint

This inspection is not directly for the purpose of check-
ing the capacity of the transmitter battery, but is per-
formed when remote control operation becomes difficult
or impossible, in order to ascertain if this is caused by
low battery capacity.

1.

Remove the transmitter screw.

2.

/Remove the cover.

3.

Remove the O–ring and battery.

1.

Connect 2 new 1.5 V dry–cell batteries in series.
Connect the battery 

 terminal to the battery re-

ceptacle side terminal and the battery 



 terminal to

the bottom terminal to provide 3 V to the transmitter.

2.

In the condition (1), push the wireless door lock re-
mote control switch on the side of the transmitter
body and operate the door lock by remote control.

Remove control operation possible.

Replace the battery for transmitter (See page 

BE–450

).

Replace transmitter and ROM in ECU

(See page 

BE–450

).

–

BODY ELECTRICAL SYSTEM

Wireless Door Lock Control System

BE–447

WIRING DIAGRAM

Check defogger wire (See page 

BE–173

).

NG

OK

Repair defogger wire.

Replace antenna pinjack cable and
capacitor.

1

INSPECTION OF ANTENNA CIRCUIT

Antenna Circuit

      CIRCUIT DESCRIPTION

The antenna receives the electromagnetic wave emitted by the transmitter and sends it to the wireless
door lock ECU.

      DIAGNOSTIC CHART

HINT: Perform this inspection only when vehicle antenna is judged to be faulty in initial check type II.

BE–448

–

BODY ELECTRICAL SYSTEM

Wireless Door Lock Control System