ECU LEXUS SC400 1991 Service Repair Manual

Fuel Pressure Control VSV Circuit
CIRCUIT DESCRIPTION
The ECU turns on a VSV (Vacuum Switching Valve)
to draw the air into the diaphragm chamber of the
pressure regulator if it detects that the temperature of
the coolant is too high during engine starting.
The air drawn into the chamber increases the fuel
pressure to prevent fuel vapor lock at high engine
temperature in order to help the engine start when it
is warm.
Fuel pressure control ends approx. 100 secs. after
the engine is started.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Check operation for fuel pressure control
VSV.Replace fuel pressure control VSV.
Repair or replace harness or
connector.
Proceed to next circuit inspection
shown on matrix chart (See page
TR±35).
Check for open and short in harness and
connector between main relay and ECU.
Check voltage of VSV power source.
Check and replace ECU.
WIRING DIAGRAM
TR±142±
ENGINE TROUBLESHOOTING Circuit Inspection
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NGOK
OKNG
2Check voltage between terminal FPU of engine & ECT ECU connector and body gro\
und.
C
OK
Hint
P(2) Connect the Check Harness A.(See page TR±30)
(2) Turn ignition switch on.
Measure voltage between terminal FPU of engine &
ECT ECU connector and body ground.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix chart
(See page TR±35).
3
Check for open and short in harness and connector between engine & ECT ECU an\
d VSV, VSV
and EFI main relay (See page IN±27).
Repair or replace harness or connector
Check and replace engine & ECT ECU.
TR±144±
ENGINE TROUBLESHOOTING Circuit Inspection
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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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NGOK
OKNG
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals TE1, TE2 and E1 of check connector, TDCL.
C
OK
PTurn ignition switch on.
Measure voltage between terminals TE1, TE2 and E1
of check connector, TDCL.
Voltage: 10 ± 14 V
Check and replace engine & ECT ECT.
2Check continuity between terminal E1 of check connector, TDCL and body ground.
Repair or replace harness or connector.
3
Check for open and short in harness and connector between engine & ECT ECU and che\
ck con-
nector, TDCL (See page IN±27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±147
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(c) Remove the seal plate.
4. REMOVE PULLEY (a) Hold SST (A) with a torque wrench, and tighten SST (B)clockwise to the specified torque.
SST 09820±63010
Torque: 39 N Vm (400 kgf Vcm, 29 ft Vlbf)
(b) Check that SST (A) is secured to the rotor shaft.
(c) As shown in the illustration, mount SST (C) in a vise, and
install the alternator to SST (C).
(d) To loosen the pulley nut, turn SST (A) in the direction
shown in the illustration.
NOTICE: To prevent damage to the rotor shaft, do not
loosen the pulley nut more than one±half of a turn.
(e) Remove the alternator from SST (C).
(f) Turn SST (B) and remove SST (A and B).
(g) Remove the pulley nut and pulley.
5. REMOVE RECTIFIER END FRAME (a) Remove the four mounting nuts.
(b) Using SST, remove the rectifier end frame.
SST 09286±46011
CH±12
±
CHARGING SYSTEM Alternator
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4. INSTALL PULLEY(a) Install the pulley to the rotor shaft by tightening thepulley nut by hand.
(b) Hold SST (A) with a torque wrench, and tighten SST (B)
clockwise to the specified torque.
SST 09820±63010
Torque: 39 N Vm (400 kgf Vcm, 29 ft Vlbf)
(c) Check that SST (A) is secured to the pulley shaft.
(d) As shown in the illustration, mount SST (C) in a vise, and
install the alternator to SST (C).
(e) To torque the pulley nut, turn SST (A) in the direction shown in the illustration.
Torque: 110 N Vm (1,125 kgf Vcm, 81 ft Vlbf)
(f) Remove the alternator from SST (C).
(g) Turn SST (B) and remove SST (A and B).
5. INSTALL RECTIFIER HOLDER (a) Place the seal plate on the rectifier end frame.
(b) Install the four rubber insulators on the lead wires.
(c) Install the rectifier holder with the four screws.
CH±18
±
CHARGING SYSTEM Alternator
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ELECTRONICALLY CONTROLLED HYDRAULIC COOLING FAN
Description
In this way system, the cooling fan ECU controls the hydraulic pressure ac\
ting on the hydraulic motor, thus
controlling the speed of the cooling fan steplessly in response to the c\
ondition of the engine and air conditioner.
Operation
The hydraulic pump is driven by a drive belt (V±ribbed belt). The sole\
noid valve adjusts the volume of oil
sent from the hydraulic pump to the hydraulic motor which drives the fan dir\
ectly, thereby controlling the fan
speed. Oil which has passed through the hydraulic motor is cooled by the oil coole\
r before returning to the reservoir
tank. The solenoid valve is controlled by the computer in accordance with the E/G\
rpm, water temp. and A/C
signals. CO±22
±
COOLIING SYSTEM Electronically Controlled Hydraulic
Cooling Fan (Description, Operation)
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Electronic Control Parts
(System Circuit)
(Cooling Fan ECU)
COMPONENTS FOR REMOVAL AND
INSTALLATION
CO±60±
COOLIING SYSTEM Electronically Controlled Hydraulic Cooling Fan
(Electronic Control Parts)
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INSPECTION OF COOLING FAN ECU
1. DISCONNECT CABLE FROM NEGATIVE TERMINAL OFBATTERY
CAUTION: Work must be started after 20 seconds or longer
from the time the ignition switch is turned to the ºLOCKº posi-
tion and the negative (±) terminal cable is disconnected from
the battery.
2. DISCONNECT COOLING FAN ECU CONNECTOR (See Components on page CO±60)
(a) Remove the instrument panel under cover.
(b) Remove the lower instrument panel finish panel and glove compartment door assembly.
(c) Disconnect the cooling fan ECU connector.
3. INSPECT COOLING FAN ECU (a) Connect the cable to the negative (±) terminal of thebattery.
(b) Check the connector on the wiring harness side as shown in the chart.
Check forTester connectionConditionSpecified value
Voltage1±GroundIgnition switch ONBattery voltage
Resistance2±3Solenoid valve at cold (20 5C (68 5F))7.5±8.5

Continuity4±Ground±Continuity
Continuity5±GroundThrottle valve openNo continuityContinuity5±GroundThrottle valve closedContinuity
Resistance9±10Coolant temp. at 80 5C (176 5F)1.48±1.58 k

(c) Disconnect the cable from the negative (±) terminal of
the battery.
4. RECONNECT COOLING FAN ECU CONNECTOR
5. RECONNECT CABLE TO NEGATIVE TERMINAL OF BATTERY
±
COOLIING SYSTEM Electronically Controlled Hydraulic
Cooling Fan (Electronic Control Parts)CO±61
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EXHAUST GAS RECIRCULATION (EGR) SYSTEM
DESCRIPTION
To reduce NOx emission, part of the exhaust gases are recirculated through\
the EGR valve to the intake
manifold to lower the maximum combustion temperature.
OPERATION
Coolant Temp.ConditionEGR ValveExhaust Gas
Below 53 5C (127 5F)±CLOSEDNot recirculated
Above 55 5C (131 5F)(a)Idling, Deceleration, Neutral,
Low air volume, High Engine speedCLOSEDNot recirculatedAbove 55 C (131 F)
Except (a)OPEN*Recirculated
* The ECU calculates the appropriate number of steps according to the in\
take air volume and the engine speed, then
drives the stepping motor to maintain the EGR volume at a level appropri\
ate to the driving conditions.

±
EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±15
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