Lexus SC300 / Lexus SC400. Manual - part 64

MEMO

AB–39

SRS

 AIRBAG   –   Troubleshooting

Circuit Inspection

Diag. Code (Normal)

Source Voltage Drop

CIRCUIT DESCRIPTION

The airbag system is equipped with a voltage–increase circuit (DC–DC converter) in the center airbag
sensor assembly in case the source voltage drops.
When the battery voltage drops, the voltage–increase circuit (DC–DC converter) functions to increase
the voltage of the airbag system to normal voltage.
The diagnosis system malfunction display for this circuit is different to other circuits–when the airbag
warning light remains lit up and the diagnostic code is a normal code, source voltage drop is indicated.
Malfunction in this circuit is not recorded in the center airbag sensor assembly, and approx. 10 se-
conds after the source voltage returns to normal, the airbag warning light automatically goes off.

Code No.

Diagnosis

(Normal)

Source voltage drop.

DIAGNOSTIC CHART

Preparation.

Does airbag warning light turn on after
approx. 10 seconds?

Check battery and charging system
(See page 

CH–1

).

Check diagnostic code, and if a
malfunction code is output,
perform troubleshooting according
to malfunction code.
If a normal code is output,
replace center airbag sensor
assembly.

WIRING DIAGRAM

AB–40

SRS

 AIRBAG   –   Troubleshooting

(1) Turn ignition switch LOCK.
(2) Disconnect center airbag sensor assembly

connector.

(3) Turn ignition switch ON. But do not start engine.
(4) Measure voltage at IG

2

 or ACC on connector

wire harness side of center airbag assembly and
operate electric system (defogger, wiper,
headlight, heater, blower, etc.).
Voltage:  6 V – 11.5 V at IG

2

 and ACC.

(5) Turn electric system switch OFF.
(6) Turn ignition switch LOCK.
(7) Remove voltmeter and connect center airbag

sensor assembly.

Does airbag warning light turn off after approx. 10 seconds?

Preparation.

Turn ignition switch ON.

Operate electric system checked in [ 1 ] (4) and
check that airbag warning light goes off after
approx. 10 seconds.

Check diagnostic code, and if a malfunction
code is output, perform troubleshooting
according to malfunction code. If a normal
code is output, replace center airbag
sensor assembly.

Check battery and charging system

(See page 

CH–1

)

INSPECTION PROCEDURE

AB–41

SRS

 AIRBAG   –   Troubleshooting

Diag. Code 11

Short is Squib Circuit or Front Airbag
Sensor Circuit (to Ground)

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 11 is recorded when occurrence of ground short is detected in the squib circuit or front
airbag sensor circuit.

Code No.

Diagnosis

11

Short circuit in squib wire harness (to ground).

Squib malfunction.

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

Front airbag sensor malfunction.

Short circuit between +S wire harness and –S wire harness of front airbag sensor.

Spiral cable malfunction.

Center airbag sensor assembly malfunction.

DIAGNOSTIC CHART

Preparation.

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

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

Check squib circuit.

Check center airbag sensor assembly.

Check squib.

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.

Go to step [ 7 ] on next page.

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

AB–20

).

Go to step [ 8 ] on next page.

Replace center airbag sensor
assembly.

Replace steering wheel pad.

AB–42

SRS

 AIRBAG   –   Troubleshooting