ect LEXUS SC300 1991 Service Repair Manual

2. READ DIAGNOSTIC TROUBLE CODERead the 2±digit diagnostic trouble code as indicated by the
number of times the SRS warning light blinks. As an example,
the blinking patterns; normal, 11 and 31 are as shown on the
illustration.
wNormal code indication
The light will blink 2 times per second.
w Malfunction code indication
In the event of a malfunction, the light will blink. The number
represented by the first blink code output indicates the first
digit of a 2±digit diagnostic trouble code. After a 1.5 second
pause, the second blink code will indicate the second digit.
If there are two or more codes, there will be a 2.5 second
pause between each.
After all the codes have been output, there will be a 4.0 se-
cond pause and they will all be repeated.
HINT:
w In the event of a number of trouble codes, indication will
begin from the smaller numbered code to the larger.
w If it does not output a diagnostic trouble code or output
a diagnostic trouble code without terminal connection,
proceed to the Tc terminal circuit inspection on page
RS±121 .
Using LEXUS hand±held tester: (a) Hook up the LEXUS hand±held tester to the DLC1 or DLC2.
(b) Read the diagnostic trouble codes by following the prompts on the tester screen.
HINT: Please refer to the LEXUS hand±held tester operator's
manual for further details.
RS±60
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName

DIAGNOSTIC TROUBLE CODE
CLEARANCE
Using diagnostic check wire:(a) Connect the 2 service wires to terminals Tc and AB of DLC1.
(b) Turn the ignition switch ACC or ON And wait approx. 6 seconds.
(c) Starting with the Tc terminal, apply body ground alternately to terminal Tc and terminal AB twice each in cycles of 1.0
seconds Confirm that body ground is absolute. Finally, keep
applying body ground to terminal Tc.
HINT: When alternately grounding terminals Tc and AB, re-
lease ground from one terminal and immediately apply it to
the other terminal within an interval of 0.2 second. If diagnos-
tic trouble codes do not clear, repeat the above procedure un-
til the codes are cleared.
(d) Several seconds after performing the clearing procedure, theSRS warning light will blink in a 50 m sec cycle to indicate the
codes have been cleared.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±63
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

2HEAT METHOD: When the problem seems to occur when the suspect area is heate\
d.
Heat the component that is likely the cause of the mal-
function with a hair dryer or similar object. Check to see
if the malfunction will occur.
Notice:

Do not heat to more than 60 C (140 F) (Tempera-
ture limit that the component can be touched with a
hand.)

Do not apply heat directly to any part in the ECU.
3WATER SPRINKLING METHOD: When the malfunction seems to occur on a rainy day or in
a high±humidity condition.
Sprinkle water onto the vehicle and check to see if the
malfunction will occur.
Notice: Never apply water directly onto the
electronic components.
HINT:

If the vehicle is subject to water leakage, the leaked
water may contaminate the ECU. When testing a ve-
hicle with a water leakage problem, special caution
must be paid.
4OTHER: When a malfunction seems to occur when electrical load is excessive.
Turn on all electrical loads including the heater blower,
headlights, rear window defogger, etc. and check to see
if the malfunction will occur.
RS±66±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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

OKNG
INSPECTION PROCEDURE
1Preparation.
P1. Disconnect battery negative (±) terminal cable, andwait 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.
2Check front airbag sensor circuit. (Measure resistance between terminals +SR and ±SR, +SL
and ±SL of center airbag sensor assembly connector.)
C
OK
PDisconnect center airbag sensor assembly connector.
Measure resistance between terminals +SR and ±SR,
+SL and ±SL of harness side connector o center airbag
sensor assembly.
Resistance: 755
± 885

Go to step

±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±73
WhereEverybodyKnowsYourName

OKNG
OKNG
3Check front airbag sensor circuit. (Measure resistance between terminals +SR\
and +SL of cen-
ter airbag sensor assembly connector and body ground.)
C
OK
Measure resistance between terminals +SR, +SL of
harness side connector of center airbag sensor assem-
bly and body ground.
Resistance: 1 M
or higher
Repair or replace harness or connector between center
airbag sensor assembly and front airbag sensor (See
page RS±48 ).
4Check D squib circuit.
C
OK
For the connector (on the spiral cable side) between the
spiral cable and steering wheel pad, measure the resist-
ance between D+, D± and body ground.
Resistance: 1 M
or higher
Go to step 
RS±74
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
WhereEverybodyKnowsYourName