1991 LEXUS SC400 relay

Diag. Code 43Starter Signal Circuit
CIRCUIT DESCRIPTION
When the engine is cranked, the intake air flow is slow, so fuel vaporization is poor. A rich mixture is therefore
necessary in order to achieve good startability. While the engine is being cranked, the battery voltage is applied
to terminal STA of the ECU. The starter signal is mainly used to increase the fuel inj\
ection volume for the starting
injection control and after±start injection control.
Code No.Diagnostic Code Detecting ConditionTrouble Area
43No starter signal to ECU

Open or short in starter signal circuit.

Open or short in ignition switch or main relay
circuit.

ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: This diagnostic chart is based on the premise that the engine is cranked nor\
mally. If the engine is not
cranked, proceed to the matrix chart of problem symptoms on page TR±35.
Check for the test mode.
Check for open in harness and connectors
between ECU and relay.
Check and replace ECU. Proceed to next circuit inspection shown
on matrix chart (See page
TR±35).
Repair or replace harness or
connector.
WIRING DIAGRAM
TR±100±
ENGINE TROUBLESHOOTING Circuit Inspection
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NGOK
OKNG
v
INSPECTION PROCEDURE
1Check output condition of diag. code 43.
C
OK
P
OK
C
Setting the test mode.
(2) Turn ignition switch OFF.
(2) Connect terminals TE2 and E1 of TDCL.
(2) Turn ignition switch ON.(Don't start the engine)
(2) Connect terminals TE1 and E1 of TDCL.
Check if code ª43º is output by the ªCHECKº engine
warning light.
Code ª43º is output.
Start the engine.
Check if the code ª43º disapears.
Code ª43º is not output.
Proceed to next circuit inspection shown on maxtric
chart (See page TR±35).
2Check for open in harness and connectors between engine & ECT ECU and st\
arter relay
(See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±101
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DIAGNOSTIC CHART
Check voltage of VSV for EGR Power
source.
Check resistance of VSV for EGR.
Repair or replace harness or
connector.
Replace VSV for EGR.
Check for open and short in harness and
connector between EFI main relay and ECU.
Check and replace EGR.
Check EGR system (See page EC±12).
Check resistance of EGR gas temp. sensor.
Check and replace EGR.
Check for open in harness and connector
between EGR gas temp, sensor and ECU.
Repair EGR system.
Replace EGR gas temp. sensor.
Repair or replace harness or
connector.
TR±106±
ENGINE TROUBLESHOOTING Circuit Inspection
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NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminal EGR of ECM connector and body ground.
C
OK
P1. Connect the Check Harness A. (See page TR±34).
2. Warm up engine to normal operating temperature.
Measure voltage between terminal EGR of engine (&
ECT) ECU connector and body ground.
Voltage:
Go to step
.
2Check resistance between terminals of VSV for EGR.
C
OK
PRemove VSV for EGR. (See page EC±13).
Measure resistance between terminals of VSV for EGR.
Resistance: 38.5 ± 44.5
at 20  C (68  F)
Replace VSV for EGR.
3Check for open and short in harness and connector between EFI main relay and \
VSV for EGR,
VSV for EGR and engine (& ECT) ECU. (See page IN±27)
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
TR±108±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
NGOK
OKNG
INSPECTION PROCEDURE
1Check fuel pump operation.
C
OK
P1. Turn ignition switch ON.
2. Using SST, connect terminals +B and FP of checkconnector.
SST 09843±18020
Check that there is pressure in the hose from the fuel
filter.
Fuel pressure can be felt.
Go to step
.
2Check for open and short in harness and connector between terminals +B e+B, FP  FP of
the check connector and fuel pump ECU (See page IN±27).
Go to step .
Repair or replace harness or connector.
3Check voltage of terminal +B of check connector.
C
OK
PTurn ignition switch ON.
Measure voltage between terminal +B of check connec-
tor and body ground.
Voltage: 10 ± 14 V
Check for ECU power source circuit (See page TR±120),
and check for open in harness and connector between
terminal +B of check connector and main relay.
TR±112
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ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
NGOK
OKNG
INSPECTION PROCEDURE
1Check fuel pump operation.
C
OK
P(2) Turn ignition switch ON.
(2) Using SST. connect terminals + B and FP of checkconnector.
SST 09843±18020
Check that there is projection of the head of the pulsa-
tion damper screw.
Projection of the head of the pulsation damper
screw.
Go to step 3.
2Check for open and short in harness and connector between terminals + B e + B FP e FP of
the check connector and fuel pump ECU (See page IN±27).
Go to step 5.
Repair or replace harness or connector.
3Check voltage or terminal + B of check connector.
C
OK
PTurn ignition switch ON.
Measure voltage between terminal + B of check connec-
tor and body ground.
Voltage: 10 ± 14 V
Check for ECU power source circuit
(See page TR±124), and check for open in harness and
connector between terminal + B of check connector and
main relay.
TR±116
±
ENGINE TROUBLESHOOTING Circuit Inspection
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ECU Power Source Circuit
CIRCUIT DESCRIPTION
When the ignition switch is turned on, battery voltage
is applied to the terminal IGSW 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 CHART
See next page for the DIAGNOSTIC CHART.
WIRING DIAGRAM
TR±120±
ENGINE TROUBLESHOOTING Circuit Inspection
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Check voltage of ECU power source.
Check continuity between terminals E1 and
body ground.
Check voltage of terminal IGSW.
Check IGN fuse.
Check ignition switch.
Check for open in harness and connector
between battery and ECU.
Check voltage of terminal M±REL.
Check EFI fuse.
Check EFI main relay.Check for open and short in harness and
connector between terminal M±REL and
body ground.
Check and repair harness or connector
between EFI fuse and battery.
Repair or replace harness or
connector.
Replace EFI main relay.
Check for short in all the harness
and components connected to the
EFI fuse.
Check and replace ECU.
Replace ignition switch.
Check for short in all the harness and
components connected to IGN fuse.
Repair or replace harness or
connector.
Proceed to next circuit inspection
shown on matrix cart (See page
TR±39
).
DIAGNOSTIC CHART
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±121
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