warning LEXUS SC400 1991 Service Repair Manual

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
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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±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTING
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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)
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±69
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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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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
Troubleshooting for this system is different for when the SRS warning light does not light up and for when dia\
g-
nostic trouble code 22 is output. Confirm the problem symptoms first before selecting the appropriate trouble-
shooting procedure.
HINT: If SRS warning light does not light up, perform the following troubles\
hooting:
(See page RS±65)
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±103
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OKNG
OKNG
INSPECTION PROCEDURE
HINT: If SRS warning light does not light up, perform the following troublesh\
ooting:
1Check ECU±B fuse.
Go to step

2Preparation.
P1. Disconnect battery negative (±) terminal cable, and
wait 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.
3Check connection of center airbag sensor assembly connector.
Repair.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±105
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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±
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TE1, TE2 Terminal Circuit
CIRCUIT DESCRIPTION
Terminal TE1 is located in the check connector in the engine compartment and terminals T\
E1 and TE2 are lo-
cated in the TDCL in the cabin. When these terminals are connected with \
the E1 terminal, diagnostic codes in
normal mode or test mode can be read from the ºCHECKº engine warning lig\
ht on the combination meter.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: If terminals TE1 and TE2 are connected with terminal E1, diagnostic code is not output or test mode isnot activated.
Even though terminal TE1 is not connected with terminal E1, the ºCHEC\
Kº engine warning light blinks.
For the above phenomenon, the likely cause is an open or short in the wire \
harness, or malfunction inside
the ECU.
Check continuity between terminal E1 and
body ground.
Repair or replace harness or
connector.Check for open and short in harness and
connector between check connector TDCL
and ECU.
Check voltage of terminals TE1, TE2.
Check and replace ECU.
Repair or replace harness or
connector.
Check and replace ECU.
WIRING DIAGRAM
TR±146±
ENGINE TROUBLESHOOTING
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DIAGNOSIS SYSTEM
DESCRIPTION
The ECU contains a built±in self±diagnosis system by which
troubles with the engine signal network are detected and a
ºCHECKº engine warning light on the instrument panel lights up.
By analyzing various signals as shown in the later table (See page
TR±14) the Electronic Control Unit (ECU) detects system malfunc-
tions relating to the sensors or actuators.
In the normal mode, the self±diagnosis system monitors 22 (USA
specification vehicles with TRAC control) or 21 (USA (except for
California) and Canadian specification vehicles with TRAC con-
trol) items, indicated by code No. as shown in TR±14. A ºCHECKº
engine warning light informs the driver that a malfunction has been
detected. The light goes off automatically when the malfunction
has been repaired. But the diagnostic code(s) remains stored in
the ECU memory (except for code Nos. 16 and 53). The ECU
stores the code(s) until it is cleared by removing the EFI fuse with
the ignition switch off.
The diagnostic code can be read by the number of blinks of the
ºCHECKº engine warning light when TE1 and E1 terminals on the
TDCL or check connector are connected. When 2 or more codes
are indicated, the lowest number (code) will appear first.
In the test mode, 15 (USA specification vehicles with TRAC con-
trol) or 14 (USA (except for California) and Canadian specification
vehicles with TRAC control) items, indicated by code No. as
shown in TR±14 are monitored. If a malfunction is detected in any
one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26,
27, 28, 29, 35, 41, 42, 47, 71 and 78 (USA specification vehicles)
or 13, 21, 22, 24, 25, 26, 27, 28, 29, 35, 41, 42, 47 and 78 (USA
(except for California) and Canadian specification vehicles) the
ECU lights the ºCHECKº engine warning light to warn the techni-
cian that malfunction has been detected. In this case, TE2 and E1
terminals on the TDCL should be connected as shown later. (See
page TR±12 ).
In the test mode, even if the malfunction is corrected, the malfunc-
tion code is stored in the ECU memory even when the ignition
switch is off (except code Nos. 43 and 51). This also applies in the
normal mode. The diagnostic mode (normal or test) and the output
of the ºCHECKº engine warning light can be selected by connect-
ing the TE1, TE2 and E1 terminals on the check connector or
TDCL, as shown later.
A test mode function has been added to the functions of the self±
diagnosis system of the normal mode for the purpose of detecting
malfunctions such as poor contact, which are difficult to detect in
the normal mode. This function fills up the selfdiagnosis system.
The test mode can be implemented by the technician following the
appropriate procedures of check terminal connection and opera-
tion described later. (See page TR±12)
TR±10
±
ENGINE TROUBLESHOOTING Diagnosis System
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Diagnosis Inspection (Normal Mode)
ºCHECKº ENGINE WARNING LIGHT
CHECK
1. The ºCHECKº engine warning light will come on when theignition switch is turned ON and the engine is not running.
HINT: If the ºCHECKº engine warning light does not light up,
proceed to troubleshooting of the combination meter (See
page
BE±146).
2. When the engine is started, the ºCHECKº engine warning light should go off.
If the light remains on, the diagnosis system has detected a
malfunction or abnormality in the system.
DIAGNOSTIC CODE CHECK
1. Turn ignition switch on.
2. Using SST, connect terminals between TE1 and E1 of TDCLor check connector.
SST 09843±18020
3. Read the diagnostic code from ºCHECKº engine warning light.
HINT: If a diagnostic code is not output, check the TE1 termi-
nal circuit (See page TR±146).
As an example, the blinking patterns for codes;normal, 12
and 31 are as shown on the illustration.
4. Check the details of the malfunction using the diagnostic
code table on page TR±14.
5. After completing the check, disconnect terminals TE1 and E1, and turn off the display.
HINT: In the event of 2 or more malfunction codes, indication
will begin from the smaller numbered code and continue in
order to the larger.
±
ENGINE TROUBLESHOOTING Diagnosis SystemTR±11
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