light 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
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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
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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.
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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.
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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±
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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
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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±
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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)
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OKNG
OKNG
4Check front airbag sensor.
C
OK
PDisconnect front airbag sensor connector.
Measure resistance between each terminal of front air-
bag sensor.
Notice:
Do not touch ohmmeter probes strongly against
terminals of front airbag sensor.
 Make sure the front airbag sensor connector is
properly connected.
Replace front airbag sensor.
5Check harness between center airbag sensor assembly and front airbag sen\
sor.
C
OK
P5. Disconnect center airbag sensor assembly con- nector.
6. Using service wires, connect +SR and ±SR, +SL and ±SL on the wire harness side of the center air-
bag sensor assembly connector.
Measure resistance between terminals +SR and ±SR,
+SL and ±SL of harness side connector of front airbag
sensor.
Notice:
 Lightly t ouch ohmmeter proves at position shown
in illustration.
 Make sure the front airbag sensor connector is
properly connected.
Resistance: Below 1

Repair or replace harness or connector between center
airbag sensor assembly and front airbag sensor. (See
page RS±48 ).
Replace front airbag sensor connector (See page RS±48).
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DTC22SRS Warning Light System Malfunction
CIRCUIT DESCRIPTION
The SRS warning light is located on the combination meter.
When the supplemental restraint system is normal, the SRS warning light ligh\
ts up for approx. 6 seconds after
the ignition switch is turned from LOCK position to ACC or ON position, and then turn\
s off automatically. If there
is a malfunction in the supplemental restraint system, the SRS warning l\
ight 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.
The SRS warning light circuit is equipped with an electrical connection che\
ck mechanism which detects when
the connector to the center airbag sensor assembly is not properly connecte\
d.
If the connector to the center airbag sensor assembly is not properly conn\
ected, the SRS warning light will not
light up.
Diagnostic trouble code 22 is recorded when a malfunction occurs in the SRS warnin\
g light system. 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 22) c\
annot be confirmed.
DTC No.Trouble Area
22 Open circuit in SRS warning light system.
 Center airbag sensor assembly malfunction.
RS±102±
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