ignition LEXUS SC300 1991 Service Repair Manual

OKNG
YESNO
YESNO
4Check SRS warning light circuit.
C
OK
P1. Disconnect center airbag sensor assembly.
2. Connect negative (±) terminal cable to battery.
3. Turn ignition switch ACC or ON.
Measure voltage LA terminal of harness side connector
of center airbag sensor assembly.
Voltage: Battery positive voltage.
Repair SRS warning light circuit.
5Does SRS warning light come on?
C
OK
P1. Disconnect negative (±) terminal cable from bat-tery.
2. Connect center airbag sensor assembly.
3. Connect negative (±) terminal cable to battery.
4. Turn ignition switch ACC or ON.
Check operation of SRS warning light.
SRS warning light comes on.
Check terminal LA of center airbag sensor assembly and
electrical connection check mechanism. If normal, re-
place center airbag sensor assembly.
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.
6Is new ECU±B fuse burnt out again?
Using simulation method, reproduce malfunction symp-
toms (See page RS±65).
Check harness between ECU±B fuse and SRS warning light, and ECU±B fuse a\
nd center airbag sensor
assembly.
RS±106±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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YESNo
HINT: If diagnostic trouble code 22 is output, perform the following troubles\
hooting:
1Is diagnostic trouble code 22 output again?
C
PClear malfunction.
1. Turn ignition switch LOCK, and wait at least 20 sec-onds.
2. Turn ignition switch ACC or ON, and wait at least 20 seconds.
3. Using SST, connect terminals Tc and E
1 of DLC2.
SST 09843±18020
4. Check diagnostic trouble code.
Using simulation method, reproduce malfunction symp-
toms (See page RS±65).
Replace center airbag sensor assembly.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±107
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DTC31Center Airbag Sensor Assembly Malfunction
CIRCUIT DESCRIPTION
The center airbag sensor assembly consists of center airbag sensor, safing sensors, ignition control and drive
circuit, diagnosis circuit, etc.
It receives signals from the airbag sensors, judges whether or not the SRS must be deploy, and diagnoses sys-
tem malfunction.
Diagnostic trouble code 31 is recorded when occurrence of a malfunction in the cen\
ter airbag assembly is de-
tected.
DTC No.Trouble Area
31
Center airbag sensor assembly malfunction.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: When a malfunction code other than code 31 is displayed at the same time, first repair the malfunction
indicated by the malfunction code other than code 31.
(See page RS±65).
RS±108±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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YESNO
INSPECTION PROCEDURE
HINT: When a malfunction code other than code 31 is displayed at the same time, first repair the malfunction
indicated by the malfunction code other than 31.
1Is diagnostic rouble code 31 output again?
C
PClear malfunction.
1. Turn ignition switch LOCK, and wait at least 20 sec-onds.
2. Turn ignition switch ACC or ON, and wait at least 20 seconds.
3. Repeat operation in step (1) and (2) at least 5 times.
4. Using SST, connect terminals Tc and E
1 of DLC2.
SST 09843±18020
5. Check diagnostic trouble code.
Using simulation method, reproduce malfunction symp-
toms (See page RS±65).
Replace center airbag sensor assembly.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±109
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ECU Power Source Circuit
CIRCUIT DESCRIPTION
When the ignition switch is turned on, battery voltage
is applied to the terminal IG SW of the ECU, and the
main relay control circuit in the ECU sends a signal to
the terminal M±REL of the ECU, switching on the
main relay. This signal causes current to flow to the
coil, closing the contacts of the main relay and supply-
ing power to the terminals +B and +B1 of the ECU.
If the ignition switch is turned off, the ECU continues
to switch on the main relay for a maximum of 2 se-
conds for the initial setting of the ISC valve.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
See next page for the DIAGNOSTIC CHART.
WIRING DIAGRAM
TR±124±
ENGINE TROUBLESHOOTING Circuit Inspection
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
Check for short in all the harness and
components connected to IGN fuse.
Check voltage of terminal M±REL.
Check for open in harness and connector
between battery and ECU.
Check and replace ECU.
Replace ignition switch.
Repair or replace harness or
connector.
Repair or replace harness or
connector.
Check for open and short in harness and
connector between terminal M REL and body
ground.
Replace EFT main relay.
Check voltage of terminal IGSW.
Check IGN fuse.
Check continuity between terminals E1 and
body ground.
Check voltage of ECU power source.
Proceed to next circuit inspection
shown on matrix chart (See page
TR±35
).
Check ignition switch.
Check EFT fuse.
Check EFT main relay.
Check and repair or harness or connector
between EFI fuse and battery.
Check for short in all the harness and
components connected to EFI fuse.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±125
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NGOK
OKNG
NGOK
INSPECTION PROCEDURE
1Check voltage between terminals + B, + B1 and E1 of engine & ECT ECU connecto\
r.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Turn ignition switch on.
Measure voltage between terminals + B, + B1 and E1
of engine & ECT ECU connector.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix chart
2Check for open in harness and connector between terminals E1 of engine &\
ECT ECU and body
ground (See page IN±27).
Repair or replace harness or connector.
3Check voltage between terminal IG SW of engine & ECT ECU connector and b\
ody ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal IG SW of engine &
ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step 6.
TR±126
±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
4Check IGN Fuse.
C
OK
PRemove IGN fuse from J/B No.1.
Check continuity of IGN fuse.
Continuity.
Check for short in all the harness and components con-
nected to IGN fuse (See attached wiring diagram).
5Check ignition switch.
C
OK
PRemove under cover and finish panel.
Check continuity between terminals.
continuity
Replace ignition switch.
Check and repair harness and connector between
battery and ignition switch, ignition switch and en-
gine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±127
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OKNG
OKNG
6Check voltage between terminal M±REL of engine & ECT ECU connector and bod\
y ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal M±REL of engine &
ECT ECU connection and body ground.
Voltage: 10 ± 14 V
Check and replace engine & ECT ECU.
7Check EFI
C
OK
PRemove EFI fuse R/B No.2.
Check continuity of EFI fuse.
Continuity
Rep
TR±128
±
ENGINE TROUBLESHOOTING Circuit Inspection
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Check EFI fuse.
Check voltage of terminal BATT.
Check operation for the back±up.
Proceed to next circuit inspection
shown on matrix chart (See page TR±39).
Check for short in all the harness and
components connected to EFI fuse.
Check and repair harness or connector
between battery, EFI fuse and ECU.
Check and replace fuse.
WIRING DIAGRAM
Back Up Power Source Circuit
CIRCUIT DESCRIPTION
Battery voltage is supplied to terminal BATT of the ECU even when the ignition switch is off for use
by the diagnostic code memory and air±fuel ratio adaptive control val\
ue memory, etc.
DIAGNOSTIC CHART
TR±126±
ENGINE TROUBLESHOOTING Circuit Inspection
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