1991 LEXUS SC400 sensor

HOW TO PROCEED WITH TROUBLESHOOTING
Malfunction symptoms of the supplemental restraint system are difficult to confirm, so the diagnostic
trouble codes become the most important source of information when troubleshoot\
ing. Perform trouble-
shooting of the supplemental restraint system in accordance with the fol\
lowing procedure:
HINT: Do not disconnect the battery negative (±) terminal cable until st\
ep , Diagnostic Trouble Code
Check and Recording, has been completed.

CUSTOMER PROBLEM ANALYSIS
Using the CUSTOMER PROBLEM ANALYSIS CHECK SHEET (See page RS±58) for reference, ask the
customer in as much detail as possible about the problem.
WARNING LIGHT CHECK
Check the SRS warning light. If the light remains on, a malfunction is stored in the center airbag sensor,
assembly, so proceed to step . If the SRS warning light is not on, a malfunction has occurred in the SRS
warning light circuit, so perform troubleshooting for 22.
HINT: 22 is recorded when a malfunction occurs in the SRS warning light syst\
em.
If an open malfunction occurs in the SRS warning light system, the SRS w\
arning light does not light up,
so that until the malfunction is repaired, the diagnostic trouble codes (\
including 22) cannot be confirmed.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING
Check the di agnostic trouble codes and make a note of any malfunction codes which ar\
e output. If a normal
code is output, an abnormality in the power source circuit may have occurred\
, so perform troubleshooting
for source voltage in step .
If 22 is output, skip steps  and  and proceed to step .
 MALFUNCTION CODE CLEARANCE
Clear the malfunction code.
HINT: The malfunction code output in step  indicates that a malfunction has occurred in the circuit desig-
nated by the malfunction code, but does not indicate whether the malfunction \
is still occurring or whether
it was in the past.
Accordingly, it is necessary to find out the present condition of the malfunction oc\
currence by clearing the
malfunction code and performing the diagnostic code check again. If this\
operation is neglected and trou-
bleshooting is performed using only the malfunction code confirmed in step , isolating the problem com-
ponent becomes difficult and invites mistaken diagnosis.
 DIAGNOSTIC TROUBLE CODE CHECK AND RECORDING  SYMPTOM SIMULATION
After repeating ignition switch ON±OFF operation (ON: wait 20 secs, OFF: \
wait 20 secs.) 5 times, check
the diagnostic trouble codes. If any code is output, the malfunction is sti\
ll occurring, so proceed to step .
Bearing in mind that a malfunction code was registered in step , provided that the normal code is present-
ly output, use the methods described in step  to simulate the malfunction.
RS±54
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName

NOTICE: When connecting the battery after clearing the malfunction code, always\
do it with the igni-
tion switch in LOCK position. When the battery has been reconnected, turn the ignition switch to
ACC or ON position after at least 2 seconds have elapsed.
If the battery is reconnected with the ignition switch in ACC or ON posi\
tion, or the ignition switch
is turned to ACC or ON within 2 seconds of connecting the battery, it is possible that the diagnosis
system will not operate normally.
 DIAGNOSTIC TROUBLE CODE CHART
Proceed to the appropriate flow chart in step  in accordance with the malfunction code found in step 
or .
 CIRCUIT INSPECTION \b REPAIR
Find out if the problem lies in a sensor, actuator or TROUBLESHOOTING, and repair the problem. After
the problem part is repaired, reinstall the disassembled parts. Do not s\
tart work until at least 90 seconds
after the ignition switch is turned to the LOCK position and the negative (±\
) terminal cable is disconnected.
CAUTION: If incorrect procedure is used, a malfunction may occur in the system o\
r there is the dan-
ger that airbag may be accidentally deploy during the repair operation. \
Carefully read the GENERAL
DESCRIPTION (See page RS±2) and the cautions for each operation, and perform repairs in the cor-
rect order using the correct methods.
HINT: The following illustration for the CIRCUIT INSPECTION shows each conne\
ctor for the SRS squib
circuit.
 
















 
















 
















±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±55
WhereEverybodyKnowsYourName

HINT:

When the SRS warning light remains lit up and the diagnostic trouble code in\
the normal code, this means a
source voltage drop.
This malfunction is not stored in memory by the center airbag sensor assembl\
y and if the power source voltage
returns to normal, after approx. 10 seconds the SRS warning light will automati\
cally go out.

Code 22 in recorded when a malfunction occurs in the SRS warning light syste\
m. If an open malfunction occurs
in the SRS warning light system, the SRS warning light does not light up\
. so that until the malfunction is repaired,
the diagnostic trouble codes (including code 22) cannot be confirmed.

When 2 or more codes are indicated, the lowest numbered code will appear\
first.

If a code not listed on the chart is displayed, then the center airbag s\
ensor assembly is faulty.
RS±62
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName

SYMPTOM SIMULATION
ªIntermittent troubles or problemsº are the malfunctions about which the customer \
has a complaint, but which
do not occur and can not be confirmed in the workshop. The intermittent pr\
oblems also include complaints about
the SRS warning light going on and off erratically.
The self±diagnostic system stores the circuit of the intermittent pro\
blem in memory even if the ignition switch
is turned off.
And, for accurate diagnosis of the problems, ask the customer to obtain info\
rmation as much as possible follow-
ing the customer problem analysis check sheet (See page RS±58) and try to reproduce the intermittent problem.
The problem simulation methods described below are the effective ways for this nature of problem to produce
the problem conditions by applying vibration, heat, and humidity.
1VIBRATION METHOD: When vibration seems to be the major cause.
CONNECTORS
Slightly shake the connector vertically and horizontally.
(Inspection of connectors)
(a) Does the wire harness connecting with its corre-
sponding part have insufficient slack?
(b) Are the terminals dirty?
(c) Are the terminals making loose contact due to termi-
nals spread?
WIRE HARNESS
Slightly shake the wire harness vertically and horizontal-
ly. The connector joint, fulcrum of the vibration, and
body through portion are the major areas to be checked
thoroughly.
PARTS AND SENSORS
Apply vibration slightly by a finger to the part or sensor
considered to be the problem cause and check if the
malfunction will occur.
Caution: Do not apply vibration to the center
airbag sensor assembly.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±65
WhereEverybodyKnowsYourName

DIAGNOSTIC TROUBLE CODE MATRIX CHART
If a malfunction code is displayed during the diagnostic trouble code chec\
k, check the circuit listed for that
code in the table below (Proceed to the page given for that circuit).
 DTC No.\
 \
Diagnosis Page
 (Normal)*1\
 \

Source voltage drop RS±68
 11\
 \

Short in squib circuit or front airbag sensor circuit (to ground) RS±70
 12\
 \

Short in squib circuit or front airbag sensor circuit (to B+) RS±78
 13\
 \

Short in squib circuit (between D+ wire harness and D± wire harness\
) RS±85
 14\
 \

Open in squib circuit (between D+ wire harness and D± wire harness)\
 RS±92
 15\
 \

Open in front airbag sensor circuit RS±97
 22*2\
 \

SRS warning light system malfunction RS±102
 31\
 \

Center airbag sensor assembly malfunction RS±108
 53\
 \

Short in squib circuit (between P+ wire harness and P± wire harness\
) RS±110
 54\
 \

Open in squib circuit (between P+ wire harness and P± wire harness)\
 RS±115
HINT:
*
1 When the SRS warning light remains lit up and the diagnostic trouble co\
de is the normal code, this means
a source voltage drop.
*
2 Code 22 is recorded when a malfunction occurs in the SRS warning light \
system. If an open malfunction
occurs in the SRS warning light system, the SRS warning light does not light up, s\
o that until the malfunction
is repaired, the diagnostic trouble code (including 22) cannot be conf\
irmed.
PROBLEM SYMPTOM CHART
Proceed with troubleshooting of each circuit in the table below.
\
 \
Problem Symptom Inspection Item Page
\
 

\



With the ignition switch at ACC or ON, the SRS warning light
sometimes lights up after approx. 6 seconds have elapsed
SRS warning light system
(Always lit upwhen ignition switch isRS±119\
 

\



SRS warning light lights up even when ignition switch is in
the LOCK position (Always lit up when ignition switch is
LOCK position)RS±11 9
\
 \

Diagnostic trouble code not displayed.
Tc terminal circuitRS±121
\
 \

Diagnostic trouble code continuously displayed.
Tc terminal circuitRS±121
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±67
WhereEverybodyKnowsYourName

WIRING DIAGRAM
CIRCUIT INSPECTION
DTC(Normal)Source Voltage Drop
CIRCUIT DESCRIPTION
The supplemental restraint 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 volt-
age of the supplemental restraint system to normal voltage.
The diagnosis system malfunction display for this circuit is different to other circuits ± when the SRS warning
light remains lit up and the diagnostic trouble code is a normal code, source\
voltage drop is indicated. Malfunc-
tion in this circuit is not recorded in the center airbag sensor assembly, and approx. 10 seconds after the source
voltage returns to normal, the SRS warning light automatically goes off.
DTC No.Diagnosis
(Normal)Source voltage drop.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
(See page CH±1).
RS±68±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName

YESNO
INSPECTION PROCEDURE
1Preparation.
P1. Turn ignition switch LOCK.
2. Disconnect battery negative (±) terminal cable, andwait at least 90 seconds.
3. Connect battery negative (±) terminal cable.
4. Disconnect center airbag sensor assembly con- nector.
5. Turn ignition switch ON. But do not start engine.
6. Measure voltage at IG
2 or ACC on connector wire
harness side of center airbag sensor assembly and
operate electric system (defogger, wiper, headlight,
heater blower, etc.)
Voltage: 6 V ± 11.5 V at IG
2 and ACC.
7. Turn electric system switch OFF.
8. Turn ignition switch LOCK.
9. Disconnect battery negative (±) terminal cable, and wait at least 90 seconds.
10. Remove voltmeter and connect center airbag sen- sor assembly connector.
11. Connect battery negative (±) terminal cable.
2Does SRS warning light turn off after approx. 10 seconds?
C
PTurn ignition switch ACC or ON and wait at least 20 sec-
onds.
Clear malfunction code. Turn ignition switch LOCK and
wait at least 20 seconds.
Operate electric system checked in
(5) and check
that SRS warning light goes off after approx. 10 sec-
onds.
Check diagnostic trouble code, and if a malfunction code
is output, perform trouble shooting according to mal-
function code. If a normal code is output, replace center
airbag sensor assembly.
Check battery and charging system.
(See page CH±1)
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±69
WhereEverybodyKnowsYourName

DTC11Short in Squib Circuit or Front Airbag Sen-
sor Circuit (to Ground)
CIRCUIT DESCRIPTION
The squib circuit consists of the center airbag sensor assembly, spiral cable and the steering wheel pad (squib),
wire harness connector and front passenger airbag assembly (squib). It\
causes the SRS to operate when the
SRS operation conditions are satisfied.
The front airbag sensor detects the deceleration force in a frontal collisi\
on 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 o\
n page RS±10. Diagnostic
trouble code 11 is recorded when occurrence of ground short is detected in the squib ci\
rcuit or front airbag sen-
sor circuit.
DTC No.Diagnosis
11
 Short circuit in squib wire harness (to ground)
 Squib malfunction
 Short circuit in front airbag sensor +S, D
+, D±, P+, P± wire harness (to ground).
 Front airbag sensor malfunctions.
 Short circuit between +S wire harness and ±S wire harness of front ai\
rbag sensor.
 Spiral cable malfunction.
 Center airbag sensor assembly malfunction.
RS±70±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName