ignition system LEXUS SC400 1991 Service Owner's Guide

OPERATION
FUNCTION OF COMPONENTS
1. FRONT AIRBAG SENSORA front airbag sensor is mounted inside each of the front
fenders. The sensor unit is a mechanical type. When the sen-
sor detects deceleration force above a predetermined limit in
a collision, the contacts in the sensor make contact, sending
a signal to the center airbag sensor assembly. The sensor
cannot be disassembled.
2. SPIRAL CABLE (in COMBINATION SWITCH) A spiral cable is used as an electrical joint from the vehicle
body side to the steering wheel.
3. STEERING WHEEL PAD (with AIRBAG) The inflater and bag of the airbag system are stored in the
steering wheel pad and cannot be disassembled.
The inflater contains a squib, igniter charge, gas generant,
etc., and inflates the bag in case of a frontal collision.
4. AIRBAG WARNING LIGHT The airbag warning light is located on the combination meter.
It goes on to alert the driver of trouble in the system when a
malfunction is detected in the center airbag sensor assembly
self±diagnosis. In normal operating condition when the igni-
tion switch is turned to the ACC or ON position, the light goes
on for about 6 seconds and then goes off.
5. CENTER AIRBAG SENSOR ASSEMBLY The center airbag sensor assembly is mounted on the floor
inside the center cluster. The center airbag sensor assembly
consists of a center airbag sensor, safing sensors, ignition
control and drive circuit, diagnosis circuit, etc. It receives sig-
nals f rom the airbag sensors, judges whether the airbag must
be activated or not and diagnoses system malfunctions. AB±5
± OperationSRS AIRBAG
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REMOVAL AND INSTALLATION OF
COMPONENT PARTS
Steering Wheel Pad and Spiral Cable
Removal and install the parts as shown.
(MAIN POINTS OF REMOVAL AND
INSTALLATION)
CAUTION: Work must be started after approx. 20 se-
conds or longer from the time the ignition switch is
turned to the LOCK position and the negative (±) terminal
cable is disconnected from the battery (See page AB±2).
NOTICE:
wIf the wiring connector of the airbag system is discon-
nected with the ignition switch at ON or ACC, diagnostic
codes will be recorded.
wNever use airbag parts from another vehicle. When re-
placing parts, replace with new parts.
1. REMOVE STEERING WHEEL PAD (a) Remove negative terminal (±) from the battery.
(b) Place the front wheels facing straight ahead.
(c) Using a torx wrench, loosen the four screws.
Torx wrench: T30 (Part No. 09042±00010 or locally manufac-
tured tool)
(d) Loosen the torx screws until the groove along the screwcircumference catches on the screw case.
AB±14
SRS AIRBAG
± Removal and Installation of Component Parts
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Front Airbag Sensor
Remove and install the parts as shown.
(MAIN POINTS OF REMOVAL AND
INSTALLATION)
CAUTION: Work must be started after approx. 20 se-
conds or longer from the time the ignition switch is
turned to the LOCK position and the negative (±) terminal
cable is disconnected from the battery (See page AB±2).
NOTICE:
wIf the wiring connector of the airbag system is discon-
nected with the ignition switch at ON or ACC, diagnostic
codes will be recorded.
wNever use airbag parts from another vehicle. When
replacing parts, replace with new parts.
wNever reuse the sensor involved in a collision when the
airbag has deployed.
wNever repair a sensor in order to reuse it.
AB±16SRS AIRBAG ± Removal and Installation of Component Parts
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How To Proceed With Troubleshooting
Malfunction symptoms of the airbag system are difficult to confirm, so the diagnostic codes become the most
important source of information when troubleshooting. Perform troubleshooting of the airbag system in ac\
cor-
dance with the following procedure:
HINT: Do not disconnect the battery negative (±) terminal cable until st\
ep [ 3 ], Diagnostic Code Check and Re-
cording, has been completed.1. CUSTOMER PROBLEM ANALYSIS Using the CUSTOMER PROBLEM ANALYSIS CHECK SHEET (See page AB±29) for reference, ask the
customer in as much detail as possible about the problem.
2. WARNING LIGHT CHECK Check the airbag warning light. If the light remains on, a malfunction is sto\
red in the center airbag sensor,
assembly, so proceed to step [ 3 ]. If the airbag warning light is not on, a malf\
unction has occurred in the
airbag warning light circuit, so perform troubleshooting for code 22.
HINT: Code 22 is recorded when a malfunction occurs in the airbag warning li\
ght system.
If an open malfunction occurs in the airbag warning light system, the airb\
ag warning light does not light up,
so that until the malfunction is repaired, the diagnostic codes (includin\
g code 22) cannot be confirmed.
3. DIAGNOSTIC CODE CHECK AND RECORDING Check the diagnostic codes and make a note of any malfunction codes which are\
output. If a normal code
is output, an abnormality in the power source circuit may have occurred, so perform troubleshootin\
g for
source voltage in step [ 8 ].
If code 22 is output, skip steps [ 4 ] and [ 5 ] and proceed to step [ 7\
].
4. CLEARING OF MALFUNCTION CODE (EXCEPT CODE 41) Clear the malfunction code.
HINT: The malfunction code output in step [ 3 ] 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 [ 3 ], isola\
ting the problem com-
ponent becomes difficult and invites mistaken diagnosis.
5. DIAGNOSTIC CODE CHECK AND RECORDING [ 6 ] SYMPTOM SIMULATION After repeating ignition switch ON±OFF operation (ON: wait 20 secs., OFF: wait 20 secs.) 5 times, check
the diagnostic codes. If any code other than code 41 is output, the malfunc\
tion is still occurring, so proceed
to step [ 7 ].
If code 41 only is output, the following three cases are possible:
w Intermittent trouble occurred previously, but it is now normal.
w The problem has been corrected, but clearing of code 41 has been forgott\
en.
w There is a malfunction in the circuit for code 41.
Focusing on the circuit of the malfunction code stored in step 3, use th\
e simulation method in step [ 6 ]
in order to simulate the malfunction. If the malfunction occurs, proceed t\
o step [ 7 ]; if not, proceed to step.
[ 12 ]. AB±25
SRS AIRBAG
± Troubleshooting
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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.
HINT: Determine the malfunction in the airbag system in step [ 6 ] by whethe\
r or not a malfunction code
other than code 41 is output.
7. DIAGNOSTIC CODE CHART Proceed to the appropriate flow chart in step [ 8 ] in accordance with the malfunction code found in step
[ 5 ] or [ 6 ].
8. CIRCUIT INSPECTION [ 9 ] REPAIR Find out if the problem lies in a sensor, actuator or wire harness and connector, and repair the problem.
After the problem part is repaired, reinstall the disassembled parts. Do not \
start work until at least 20 se-
conds after the ignition switch is turned to the LOCK position and the negati\
ve (±) terminal cable is discon-
nected.
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 activated during the repair operation. Carefully read the GEN-
ERAL DESCRIPTION (See page AB±2) and the cautions for each operation, and perform repairs in
the correct order using the correct methods.
HINT: The following illustration for the CIRCUIT INSPECTION shows each conne\
ctor for the circuit from
the center airbag sensor assembly to the steering wheel pad (squib).
10 CLEARING OF MALFUNCTION CODE (EXCEPT CODE 41) When all the malfunction codes found in steps [ 5 ] and [ 6 ] have been repa\
ired, clear the malfunction
codes.
AB±26
SRS AIRBAG
± Troubleshooting
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11. DIAGNOSTIC CODE CHECKAfter repeating ignition switch ON±OFF operation (ON: wait 20 secs., OFF: wait 20 secs.) 5 times, check
the diagnostic codes. If only code 41 is displayed, proceed to step [ 12 ]. If a code other than code 41 is
displayed, return to step [ 7 ] and troubleshoot the displayed malfuncti\
on code.
NOTICE: When connecting the battery after clearing the malfunction code,\
always do it with the ignition
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 positi\
on, or the ignition switch is turned
ACC or ON within 2 seconds of connecting the battery, it is possible that the diagnosis system will not oper-
ate normally.
12. CLEARING OF MALFUNCTION CODE 41 STORED IN MEMORY Clear malfunction code 41 stored in memory. This operation is not necessary only in case that the power
source voltage returns to normal.
13. CONFIRMATION TEST Check the warning light again and confirm that all the malfunctions have been\
repaired. If the warning light
indicates an abnormality, repeat the operation again from step [ 2 ]. If code 41 is output at st\
ep [ 3 ], skip
steps [ 4 ] and [ 5 ] and proceed to step [ 7 ]. AB±27
SRS AIRBAG
± Troubleshooting
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Diagnosis Inspection
AIRBAG WARNING LIGHT CHECK
(a) Turn the ignition switch to ACC or ON and check that theairbag warning light lights up.
(b) Check that the airbag warning light goes out after approx. 6 seconds.
HINT:
wWhen the ignition switch is at ACC or ON and the airbag
warning light remains on, the center airbag sensor
assembly has detected a malfunction code.
wIf, after approx. 6 seconds have elapsed, the airbag
warning light sometimes lights up or the airbag warning
light lights up even when the ignition switch is OFF, a
short in the airbag warning light circuit can be
considered likely. Proceed to Airbag warning light
system (always lit up) on page AB±84.
DIAGNOSTIC CODE CHECK
1. OUTPUT DIAGNOSTIC CODE
(a) Turn the ignition switch to ACC or ON position and waitapprox. 20 seconds.
(b) Using SST, connect terminals Tc and E
1 of the TDCL.
SST 09843±18020
NOTICE: Never make a mistake with the terminal connec-
tion position as this will cause a malfunction.
2. READ DIAGNOSTIC CODE Read the diagnostic code as indicated by the number of
times the airbag warning light blinks.
wNormal code indication
The light will blink 2 times per second.
wMalfunction code indication
In the event of a malfunction, the light will blink. The first
number of the code No. will equal the first digit of a
2±digit diagnostic code, and after a 1.5 second pause,
the 2nd number of the code No. will equal the 2nd 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:
wIn the event of a number of trouble codes, indication will
begin from the smaller numbered code to the larger.
wIf a diagnostic code is not output or is continuously
output, proceed to the TC terminal circuit inspection on
page AB±86 .
AB±30
SRS AIRBAG
± Troubleshooting
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CLEARING OF DIAGNOSTIC CODE
1. CLEARING OF MALFUNCTION CODE(EXCEPT CODE 41)
Remove the battery negative (±) terminal or ECU±B fuse for
10 seconds or more with the ignition switch OFF.
NOTICE: When connecting the battery after cancelling
the malfunction code, always do it with the ignition
switch in LOCK position. If the battery is connected with
the ignition switch in ACC or ON position, there are cases
when the diagnosis system does not operate normally.
HINT:
wCode 41 cannot be cleared by this method.
wThe lower the temperature, the longer the battery
negative (±) terminal must be left off.
wOther memory systems (clock, audio system) will also
be cancelled out (See page AB±2).
2. CLEARING OF MALFUNCTION CODE 41 STORED IN MEMORY
(a) Connect service wires to terminals Tc and AB of theTDCL.
(b) Turn the ignition switch ACC or ON and wait approx. 6 seconds.
(c) S ta rtin g with th e Tc te rmin a l, ap p ly bo d y gr ound
alternately to terminal Tc and terminal AB twice each in
cycles of 1.0 ± 0.5 seconds. Finally, keep applying body
ground to terminal Tc.
HINT: When alternating between body ground of terminals Tc
and AB release one from body ground while applying it to the
other terminal. The time interval in between must be within
the following conditions. If it is out of the conditions, code 41
will not be cleared.
(d) After several seconds, when the airbag warning light
starts to blink in a 64 msec. cycle, cancellation is
completed.
HINT: This method clears not only code No. 41, but also other
malfunction codes all at once.
Except when instructed by the troubleshooting procedure,
use this method only when the repair procedure is completed
(See page AB±25).
AB±32
SRS AIRBAG
± Troubleshooting
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Diagnostic Code Matrix Chart
If a malfunction code is displayed during the diagnostic code check, check\
the circuit listed for that code in the
table below (Proceed to the page given for that circuit).
Code No.DiagnosisPage
(Normal)*1Source voltage dropAB±40
11Short in squib circuit or front airbag sensor circuit (to ground)AB±42
12Short in squib circuit or front airbag sensor circuit (to +B)AB±48
13Short in squib circuit (between D+ wire harness and D± wire harness)\
AB±54
14Open in squib circuitAB±62
15Open in front airbag sensor circuitAB±68
22*2Airbag warning light system malfunctionAB±74
31Center airbag sensor assembly malfunctionAB±80
41*3Malfunction stored in memoryAB±82
HINT:
*1 When the airbag warning light remains lit up and the diagnostic code is the normal code, this means asource voltage drop.
*2 Code 22 is recorded when a malfunction occurs in the airbag warning light sy\
stem. If an open malfunction occurs in the airbag warning light system, the airbag warning light does not light up, so that until the mal-
function is repaired, the diagnostic code (including code 22) cannot be confir\
med.
*3 When a malfunction occurs in the airbag system, malfunction codes 11 to 31 are output. After repairing the malfunction indicated by malfunction codes 11 to 31, codes 11 to 31 are cleared from the memory, but
code 41 is output instead. Once the malfunction has been detected, the airba\
g warning light will remain
lit up until code 41 is cleared, even though the malfunction has been re\
paired.
Problem Symptom Chart
Proceed with troubleshooting of each circuit in the table below.
Problem SymptomInspection ItemPage

With the ignition switch at ACC or ON, the airbag warning light
sometimes lights up after approx. 6 seconds have elapsed.

Airbag warning light lights up even when ignition switch is in the
LOCK position.
Airbag warning light system
(Always lit up)AB±84

Diagnostic code not displayed.

Diagnostic code continuously displayed.
Tc terminal circuitAB±86
AB±34SRS AIRBAG ± Troubleshooting
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(1) Turn ignition switch LOCK.
(2) Disconnect center airbag sensor assemblyconnector.
(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±41SRS AIRBAG ± Troubleshooting
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