Lexus SC300 / Lexus SC400. Service manual — part 66

Check squib circuit.

Disconnect connector between center airbag sen-
sor assembly and spiral cable.

Measure resistance between D+, D– on spiral
cable side of connector between spiral cable and
steering wheel pad and body ground.

Repair or replace spiral cable.

Repair or replace harness or connector between
center airbag sensor assembly and spiral cable,

Resistance: 1 M

or higher

AB–47

SRS

AIRBAG – Troubleshooting

Diag. Code 12

Short in Squib Circuit or Front Airbag
Sensor Circuit (to +B)

CIRCUIT DESCRIPTION

The squib circuit consists of the center airbag sensor assembly, spiral cable and the steering wheel
pad (squib). It causes the airbag to deploy when the airbag deployment conditions are satisfied.
The front airbag sensor detects the deceleration force in a frontal collision and is located in the front
fender on the left and right sides.
For details of the function of each component, see FUNCTION OF COMPONENTS on page

AB–5

.

Diagnostic code 12 is recorded when a +B short is detected in the squib circuit or the front airbag
sensor circuit.

Code No.

Diagnosis

12

Short circuit in squib wire harness (to +B)

Squib malfunction.

Short circuit in front airbag sensor +S wire harness (to +B).

Open circuit in RH and LH front airbag sensor harness.

Spiral cable malfunction.

Center airbag sensor assembly malfunction.

AB–48

SRS

AIRBAG – Troubleshooting

DIAGNOSTIC CHART

Preparation.

Check front airbag sensor circuit.
(Measure voltage between terminal +SR
or +SL of center airbag sensor assembly
connector and body ground).

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.

Repair or replace harness or connector
between center airbag sensor assembly and
spiral cable.

Check front airbag sensor circuit.
(Measure resistance between terminals +SR
and –SR, +SL and –SL of center airbag
sensor assembly connector).

Check squib circuit.

Check center airbag sensor assembly.

Check squib.

Check spiral cable.

Repair or replace spiral cable.

Go to step [ 7 ].

Replace center airbag sensor
assembly.

Replace steering wheel pad.

Go to Code 15 (See page

AB–68

).

Repair or replace harness or
connector between center airbag
sensor assembly and front airbag
sensor (See page

AB–20

).

WIRING DIAGRAM

AB–49

SRS

AIRBAG – Troubleshooting

(1) Disconnect battery negative (–) terminal cable,

and wait at least 20 seconds.

(2) Remove steering wheel pad (See page

AB–14

).

Check front airbag sensor circuit. (Measure resistance between terminals +SR and
–SR, +SL and –SL of center airbag sensor assembly connector.

Preparation.

Disconnect center airbag sensor assembly con-
nector.

Measure resistance between terminals +SR and
–SR, +SL and –SL of harness side connector of
center airbag sensor assembly.

Go to Code 15 (See page

AB–68

).

When storing steering wheel pad, keep upper
surface of the pad facing upward.

Resistance: 755

– 855

Check front airbag sensor circuit. (Measure voltage between terminal +SR or +SL
of center airbag sensor assembly connector and body ground.

(1) Connect negative (–) terminal cable to

battery.

(2) Turn ignition switch ON.

Repair or replace harness or connector
between center airbag sensor assembly

and front airbag sensor (See page

AB–20

).

Resistance: 1 V

Measure voltage between terminals +SR or +SL
of harness side connector of center airbag sensor
assembly and body ground.

INSPECTION PROCEDURE

AB–50

SRS

AIRBAG – Troubleshooting