Lexus SC300 / Lexus SC400. Service manual — part 774

OK

NG

1

Preparation.

P

1.

Disconnect battery negative (–) terminal cable, and
wait at least 90 seconds.

2.

Remove steering wheel pad (See page

RS–19

).

3.

Disconnect connectors of front passenger airbag
assembly (See page

RS–32

).

Caution:

Store the steering wheel pad with the

surface facing upward.

2

Check P squib circuit.

C

OK

P

Disconnect center airbag sensor assembly connector.

Measure resistance between P

+

and P

–

on center air-

bag sensor assembly side of connector between center
airbag sensor assembly and front passenger airbag as-
sembly.

Resistance:

Below 1

Repair or replace harness or connector between center
airbag sensor assembly and front passenger airbag as-
sembly.

–

SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING

RS–117

OK

NG

OK

NG

3

Check center airbag sensor assembly.

C

OK

Hint

P

1.

Connect connector to center airbag sensor connec-
tor.

2.

Connect connector between center airbag sensor
assembly and wiring harness connector.

3.

Using a service wire, connect D

+

and D

–

, P

+

and P

–

.

4.

Connect negative (–) terminal cable to battery, and
wait at least 2 seconds.

1.

Turn ignition switch ACC or ON and wait at least 20
seconds. Clear malfunction code. Turn ignition
switch LOCK and wait at least 20 seconds.

2.

Turn ignition switch ACC or ON , and wait at least
20 seconds.

3.

Using SST, connect terminals Tc and E

1

of DLC2.

SST 09843–18020

4.

Check diagnostic trouble code.

Diagnostic trouble code 54 is not output.

Codes other than code 54 may be output at this time, but
this is not relevant to this check.

Replace center airbag sensor assembly.

4

Check P squib.

C

OK

Hint

P

1.

Turn ignition switch LOCK.

2.

Disconnect battery negative (–) terminal cable, and
wait at least 90 seconds.

3.

Connect front passenger airbag assembly connec-
tor.

4.

Connect negative (–) terminal cable to battery, and
wait at least 2 seconds.

1.

Turn ignition switch ACC or ON and wait at least 20
seconds. Clear malfunction code. Turn ignition
switch LOCK and wait at least 20 seconds.

2.

Turn ignition switch ACC or ON, and wait at least 20
seconds.

3.

Using SST, connect terminals Tc and E

1

of DLC2.

SST 09843–18020

4.

Check diagnostic trouble code.

Diagnostic trouble code 54 is not output.

Codes other than code 54 may be output at this time, but
this is not relevant to this check.

Replace front passenger airbag assembly.

From the results of the above inspection, the malfunctioning part can now be considered normal. To
make sure of this, use the simulation method to check.

RS–118

–

SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING

WIRING DIAGRAM

SRS Warning Light System (Always Lit Up, when ignition switch in
LOCK position)

CIRCUIT DESCRIPTION

The SRS warning light is located on the combination meter.
When the supplemental restraint system is normal, the SRS warning light lights up for approx. 6 seconds after
the ignition switch is turned from LOCK position to ACC or ON position, and then turns off automatically.
If there is a malfunction in the supplemental restraint system, the SRS warning light lights up to inform the driver
of the abnormality.
When terminals Tc and E

1

of the DLC2 are connected, the diagnostic trouble code is displayed by the blinking

of the SRS warning light.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

HINT: If the SRS warning light is always lit up by a DTC check procedure, perform Tc Terminal circuit check proce-
dure (See page

RS–121

).

–

SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING

RS–119

YES

NO

INSPECTION PROCEDURE

1

Does SRS warning light turn off?

C

Hint

P

1.

Turn ignition switch LOCK.

2.

Disconnect negative (–) terminal cable from battery
and wait at least 90 seconds.

3.

Remove steering wheel pad (See page

RS–19

).

4.

Disconnect connectors of front passenger airbag
assembly (See page

RS–32

).

5.

Disconnect center airbag sensor assembly con-
nector.

6.

Connect negative (–) terminal cable to battery.

Check operation of SRS warning light.

Ignition Switch is LOCK position.

Check SRS warning light circuit or terminal AB circuit of
DCL1 or DLC2.

Replace center airbag sensor assembly.

RS–120

–

SUPPLEMENTAL RESTRAINT SYSTEM

TROUBLESHOOTING