1991 LEXUS SC400 check engine

CIRCUIT DESCRIPTION (Cont'd)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed c\
onfirming that diag. code is nolonger detected.

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
With the A/C ON and transmission in D range (O/D OFF), drive at 40±\
70 mph for 4 min.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light up at 1±4 min. of driving at 40±70 mph (64±112 km/h).
NOTICE: If the conditions in this test are not strictly followed, detection of the\
malfunction will not be possible.
Malfunction: Open in EGR gas temp. sensor circuit
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±109
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DIAGNOSTIC CHART
WIRING DIAGRAM
Check voltage of terminal EGR 1 ~ 4.
Check voltage of EGR Step motor power
source.
Check resistance of EGR step motor.
Check for open and short in harness and
connector between EGR step motor and
ECU.
Check and replace ECU.
Check operation for EGR step motor.
Check resistance of EGR gas temp. sensor.
Check for open and short in harness and
connector between EGR gas temp. sensor
and ECU.
Check and replace ECU.
Replace EGR gas temp. sensor.
Replace EGR step motor.
Replace EGR step motor.
Repair or replace harness or
connector.
Repair or replace harness or
connector.
Check for ECU power source
circuit.
TR±110±
ENGINE TROUBLESHOOTING
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NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals EGR 1 ~ 4 of engine & ECT ECU connector and b\
ody ground.
C
OK
P(2) Connect the Check Harness A.(See page TR±30).
(2) Turn ignition switch on.
Measure voltage between terminals EGR 1 ~ 4 of en-
gine & ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Go to step 5.
2Check voltage between terminals B1 and B2 of EGR step motor connector an\
d body ground.
C
OK
P(2) Disconnect EGR step motor connector.
(2) Turn ignition switch on.
Measure voltage between terminals B1 and B2 of EGR
step motor connector and body ground.
Voltage: 10 ± 14 V
Check for ECU power source circuit
(See page TR±124).
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±111
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OKNG
OKNG
OKNG
3Check resistance of EGR step motor.
C
OK
PDisconnect EGR step motor connector.
Measure resistance between terminals shown below.
Replace EGR step motor.
4Check for open and short in harness and connector between EGR step motor and e\
ngine & ECT
ECU (See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
5Check operation for EGR step motor.
C
OK
PRemove EGR step motor.
(2) Connect the battery positive lead to terminals B1 and B2, and the negative lead to terminals S1 ± S2
± S3 ± S4 in that order.
(2) Connect the battery positive lead to terminals B1 and B2, and the negative lead to terminals S4 ± S3
± S2 ± S1 in that order.
(2) The valve moves in the closing direction.
(2) The valve moves in the opening direction.
Replace EGR step motor.
TR±112
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ENGINE TROUBLESHOOTING Circuit Inspection
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OKNG
OKNG
6Check resistance of EGR gas temp. sensor.
C
OK
PDisconnect EGR gas temp. sensor connector
(See page FI±103).
Measure resistance between terminals of EGR gas
temp. sensor connector.
Resistance: 69 ± 89 k
at 50 C (122 F)
12 ± 15 k
at 100 C (212 F)
2 ± 4 k
at 150 C (302 F)
Replace EGR gas temp. sensor.
7Check for open and short in harness and connector between EGR gas temp. sensor and\
engine
& ECT ECU (See IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±113
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DIAGNOSTIC CHART
Check fuel pump operation.
Check for open and short in harness and
connector between check connector and
fuel pump ECU.
Repair or replace harness or connector.
Check voltage of terminal +B of check
connector.
Check for open and short in harness and
connector between check connector and
fuel pump.
Repair or replace harness or connector.
Check voltage of terminal FPC.
Check for open and short in harness and
connector between ECU and fuel pump
ECU. ((FPC)
Check for open and short in harness and
connector between ECU and fuel pump
ECU. (DI)
Check and replace ECU.
Check for ECU power source
circuit.
Repair or replace fuel pump.
Replace fuel pump ECU.
Repair or replace harness or
connector.
Repair or replace harness or
connector.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±111
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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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NGOK
NGOK
OKNG
OKNG
4Check for open and short in harness and connector between terminal FP of chec\
k connector,
fuel pump and body ground (See page IN±27).
Repair or replace fuel pump.
Repair or replace harness or connector.
5Check voltage between terminals FPC and E of fuel pump ECU connector.
C
OK
P1. Remove the LH quarter trim panel. (See page FI±81 )
2. Disconnect fuel pump ECU connector.
Measure voltage between terminals FPC and E of fuel
pump ECU connector when ignition switch is turned to
start.
Voltage: 4 ± 6 V
Replace fuel pump ECU.
6Check for open in harness and connector between terminal FPC of engine (& ECT) ECU and ter-
minal FPC of fuel pump ECU, terminal E of fuel pump ECU and body ground (See\
page IN±27).
Repair or replace harness or connector.
7Check for open and short in harness and connector between terminal DI of engin\
e (& ECT) ECU
and terminal DI of fuel pump ECU (See page IN±27).
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±113
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