1991 LEXUS SC400 relay

OKNG
OKNG
6Check for open and short in harness and connector between ignition relay and \
ignition coil,
ignition coil and igniter (See page IN±27).
Repair or replace harness or connector
#Check ignition coil.
C
OK
PDisconnect ignition coil connector.
(For No. 1 ignition coil (on left bank), remove the battery)
(2) Check primary coil. Measure resistance between terminals of ignition
coil connector.
(2) Check secondary coil. Measure resistance between terminal 1 of ignition
coil connector and high±tension terminal.
Replace ignition coil.
Replace Igniter. *1
*1: When diag. code 14 is displayed, replace the igniter with 5 wire harness. (extra wire is for tachometer). When diag.
code 15 is displayed, replace the igniter with 4 wire har-
ness
TR±58±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
8Check Ignition Relay.
C
OK
P
C
OK
Remove ignition relay.
Check continuity between terminals of ignition relay
shown below.
(2) Apply battery voltage between terminals 3 and 6, 4and 5.
(2) Check continuity between terminals 1 and 2.
Replace ignition relay.
Check and repair harness or connector between
battery and ignition relay, ignition relay and igni-
ter.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±59
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OKNG
OKNG
INSPECTION PROCEDURE
1Disconnect the engine & ECT ECU connector, check voltage between terminals HTL1, HTR1 of
engine & ECT ECU connector and body ground.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Disconnect engine & ECT ECU connector.
(2) Turn ignition switch on.
Measure voltage beween terminals HTL1, HTR1 of en-
gine & ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step [3].
2Check main oxygen sensor heater.
C
OK
PDisconnect main oxygen sensor connector.
Measure resistance between terminals 1 and 2 of main
oxygen sensor connector.
Resistance: 5.1 ± 6.3
at 20 C (68 F)
Replace main oxygen sensor.
Check and repair harness or connector between
main relay and main oxygen sensor, main oxygen
sensor and engine & ECT ECU.
TR±65±
ENGINE TROUBLESHOOTING Circuit Inspection
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DIAGNOSTIC CHART
HINT: When other codes are output in addition to 27 at the same time, check the ci\
rcuits for othercodes first.
WIRING DIAGRAM
Check voltage between terminal HT.
Check resistance of sub±oxygen sensor
heater.
Check for open and short in harness and
connector between EFI main relay and ECU.
Check and replace ECU.
Check operation of sub±oxygen sensor
heater.
Check and replace ECU.
Replace sub±oxygen sensor.
Repair or replace harness or
connector.
Replace sub±oxygen sensor.*
*: In this case, oxygen sensor can bedeteriorated.
TR±78±
ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
NGOK
3Check for open and short in harness and connector between EFI main relay and engine (& ECT)
ECU (See page IN±27).
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
4Check voltage between terminal HT of engine (& ECT) ECU connector and \
body ground.
C
OK
PWarm up engine to normal operating temperature.
Measure voltage between terminal HT of engine (&
ECT) ECU connector and body ground, when engine is
idling and racing at 3,500 rpm.
Replace sub±oxygen sensor.* *: In this case, oxygen sensor can be deteriorated.
Check and replace engine (& ECT) ECU.
TR±80±
ENGINE TROUBLESHOOTING Circuit Inspection
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NGOK
OKNG
INSPECTION PROCEDURE
1Disconnect the engine & ECT ECU connector.
C
OK
P(2) Connect the Check Harness A.(See page TR±30)
(2) Disconnect engine & ECT ECU connector.
(2) Turn ignition switch on.
Measure voltage between terminals HTL2, HTR2 of en-
gine & ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step [3].
2Check sub±oxygen sensor heater.
C
OK
PDisconnect sub±oxygen sensor connector.
Measure resistance between terminals 1 and 2 of sub±
oxygen sensor connector.
Resistance: 5.1 ± 6.3
20 C (68 F)
Replace sub±oxygen sensor.
Check and repair harness or connector between
main relay and sub±oxygen sensor, sub±oxygen
sensor and engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±85
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WIRING DIAGRAM
Check for the test mode.
Check for open in harness and connector
between ECU and relay.Repair or replace harness or
connector.
Proceed to next circuit inspection shown
on matrix chart (See page
TR±39).
Check and replace ECU.
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.
DTC No.DTC Detecting ConditionTrouble Area
43No starter signal to ECU.

Open or short in starter signal circuit.

Open or short in ignition switch or starter
relay circuit.

ECU
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: This diagnostic chart is based on the premise that the engine is cranke\
d normally. If the engine is not
cranked, proceed to the matrix chart of problem symptoms on page TR±39.
TR±96
±
ENGINE TROUBLESHOOTING Circuit Inspection
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INSPECTION PROCEDURE
Check output condition of diag. code 43
Setting the test mode.
6. Turn ignition switch OFF.
7. Connect terminals TE2 and E1 of TDCL.
8. Turn ignition switch ON.(Don't start the engine)
9. Connect terminals TE1 and E1 of TDCL.
Check if code ª43º is output by the ªCHECKº en-
gine warning light.
Code ª43º is output.
Start the engine.
Check if the code ª43º disappear.
Code ª43º is not output.
Proceed to next circuit inspection shown on
matrix chart (See page
TR±39).
Check for open in harness and connector between engine (& ECT) ECU
and starter relay (See page IN±27)
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±97
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