1991 LEXUS SC400 relay

Trouble Area
ºCHECKº
Engine Warning
Light *

Memory* See PageTrouble Area
Normal
ModeTest
Mode
MemorySee Page
w Open or short in air flow meter circuit.
w Air flow meter
w ECU
ONN.A.TR±88
wECUONONTR±92
wOpen or short in throttle position sensor circuit.
wThrottle position sensorONONTR±94Throttle osition sensor
w ECU
wNo. 1 speed sensor
w Combination meter
w Open or short in No. 1 speed sensor circuit.
w ECU
ONONTR±98
wOpen or short in starter signal circuit.
w Open or short in ignition switch or main relay circuit.
w ECU
N.A.OFFXTR±100
wOpen or short in sub±throttle position sensor circuit.
wSub±throttle position sensorOFFONTR±94Sub throttle osition sensor
wECU
wOpen or short in No. 1 knock sensor circuit.wOen or short in No. 1 knock sensor circuit.
w No. 1 knock sensor (looseness)
ONN.A.No. 1 knock sensor (looseness)
wECU

w ECUONN.A.XTR±102
w Open or short in No. 2 knock sensor circuit.w Oen or short in No. 2 knock sensor circuit.
w No. 2 knock sensor (looseness)
ONN.A. No. 2 knock sensor (looseness)
w ECU

*1, 2: See page TR±20.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±19
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
Refer to inspection procedure in details.
HINT: If diag. code 14 is displayed, check No. 1 igniter circuit. If diag. code 15 is displayed, check No. 2 igniter circuit.
Check for spark.
Check for open and short in IGF signal circuit
between igniter and ECU.
Check voltage of terminal IGF.
Check and replace ECU.
Check voltage of terminal IGT.
Check voltage of igniter power source.
Check for open and short in primary coil circuit.
Check ignition coil.
Replace igniter.
Check and repair igniter power source circuit.
Check voltage of terminal IGT
(Disconnect igniter connector).
Check and repair igniter power source circuit. Repair or replace harness or
connector.
Replace igniter.
Repair or replace harness or
connector
Replace ignition relay.
Replace ignition relay.
Check for open and short in IGT signal circuit
between igniter and ECU.
Check and replace ECU. Repair or replace harness or
connectorReplace igniter.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±55
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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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