1991 LEXUS SC400 VSV

OKNG
INSPECTION PROCEDURE
1Check fuel pressure control VSV.
C
OK
P
OK
C
(2) Remove fuel pressure control VSV.
(2) Disconnect fuel pressure control VSV connector.
(2) Measure resistance between terminals.
(2) Measure resistance between each terminal and thebody.
1. Resistance: 30 ± 50 at 20C (68F)
2. Resistance: 1M or higher
Check operation of fuel pressure control VSV when bat-
tery voltage is applied to the terminals of fuel pressure
control VSV connector or not.
Battery voltage is applied:
The air from pipe E is flowing out through the air fil-
ter.
Battery voltage is not applied:
The air from pipe E is flowing out through pipe G.
Replace fuel pressure control VSV.
Go to step 2.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±143
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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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Diag. Code 71
EGR System Malfunction (Only for
USA spec.)
CIRCUIT DESCRIPTION
If even one of the following conditions is ful-
filled, the VSV is turned ON by a signal from
the ECU. This results in atmospheric air act-
ing on the EGR valve, closing the EGR valve
and shutting off the exhaust gas (EGR cut±
OFF).
w
Coolant temp. below 505C (122 5F)
w
During deceleration (throttle valve closed)
w
Light engine load (amount of intake air very
small).
w
Engine speed over 5,200 rpm. The EGR system is designed to recirculate the exhaust gas properly controll\
ed according to the driv-
ing condition back into the intake air±fuel mixture. It helps to slow dow\
n combustion in the cylinder
and thus lower the combustion temperature which, in turn, reduces the amoun\
t of NOx emission. The
amount of EGR is regulated by the EGR vacuum modulator according to the engine\
load.
Code No.Diagnostic Code Detecting ConditionTrouble Area
EGR t i 70
5C (158 5F) b l f 1 4
w
Open in EGR
gas temp. sensor circuit.EGR gas temp. is 70 5C (158 5F) or below for 1 4
min. under conditions (a) and (b).
(2 trip detection logic)*
Oen in EGR gas tem. sensor circuit.
w
Short in VSV circuit for EGR.
71
(2 trip detection logic)*
(a) Coolant temp.: 63 5C (145 5F) or more.
(b) EGR operationpossible (EX ECT in 3rd speed
Short in VSV circuit for EGR.
w
EGR hose disconnected, valve stuck.
(b) EGR operation possible (EX. ECT in 3rd speed
(5th for M/T), A/C ON, 60 mph (96 km/h), Flat
road)
EGR hose disconnected, valve stuck.
w
Clogged EGR gas passage.
road).gg g g
w
ECU
*: See page TR±25.
TR±104
±
ENGINE TROUBLESHOOTING Circuit Inspection
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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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15
ABBREVIATIONS
DISCONNECTION AND CONNECTION OF BOLT
TYPE CONNECTORS
For engine and ECT ECU in this vehicle, connectors are used
which require a bolt built into the connector to be screwed down to
securely connect the connector.
1. Disconnect the connectorAfter completely loosening the bolt, the two parts of the
connector can be separated.
NOTICE:
Do not pull the wire harness when disconnecting the
connector.
2. Connect the connector
NOTICE:
Before connecting the connector, always check that the
terminals are not bent or damaged.
(a) Match the guide section of the male connectorcorrectly with the female connector, then press them
together.
(b) Tighten the bolt. Make sure the connectors are completely connected,
by tightening the bolt until there is a clearance of less
than 1 mm (0.04 in.) between the bottom of male
connector and the end of female connector.
ABBREVIATIONS
The following abbreviations are used in this manual.
A/C = Air Conditioning O/D = Overdrive
ABS = Anti±Lock Brake System R/B = Relay Block
A/T = Automatic Transmission RH = Right±Hand
CB = Circuit Breaker SRS = Supplement Restraint System
COMB. = Combination SW = Switch
ECT = Electronic Controlled Transmission TDCL = Total Diagnostic Communication Link
ECU = Electronic Control Unit TEMP. = Temperature
EGR = Exhaust Gas Recirculation TRAC = Traction Control
FL = Fusible Link VSV = Vacuum Switching Valve
ISC = Idle Speed Control W/ = With
J/B = Junction Block W/O = Without
LH = Left-Hand
* The titles given inside the components are the names of the terminals (ter\
minal codes) and are not treatedas being abbreviations.
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226
AUTOMATIC AIR CONDITIONER
1. HEATER BLOWER MOTOR OPERATION
CURRENT IS APPLIED AT ALL TIMES THROUGH HEATER FUSE (60A) TO TERMINAL 5 OF HEATER RELAY. WHEN THE IGNITION SW IS
TURNED ON, CURRENT FLOWS THROUGH HEATER FUSE (10A) TO TERMINAL 1 OF HEATER RELAY " TERMINAL 3 " TERMINAL HR
OF A/C CONTROL ASSEMBLY. AT THE SAME TIME, CURRENT ALSO FLOWS FROM HEATER FUSE (10A) TO TERMINAL IG+ OF A/C
CONTROL ASSEMBLY AND TERMINAL 2 OF WATER VALVE VSV " TERMINAL 1 " TERMINAL WV OF A/C CONTROL ASSEMBLY.
* LOW SPEED OPERATION
WHEN THE BLOWER SW (A/C CONTROL ASSEMBLY) IS PUSHED TO LOW SPEED POSITION, THE CURRENT TO TERMINAL HR OF A/C
CONTROL ASSEMBLY FLOWS TO TERMINAL E OF A/C CONTROL ASSEMBLY " GROUND AND TURNS THE HEATER RELAY. AS A
RESULT, THE CURRENT TO TERMINAL 5 OF HEATER RELAY FLOWS TO TERMINAL 4 OF RELAY " TERMINAL 2 OF BLOWER
RESISTOR " TERMINAL 1 " GROUND AND CAUSES THE BLOWER MOTOR TO ROTATE AT LOW SPEED.
* MEDIUM (M1, M2, M3) AND HIGH SPEED OPERATION
WHEN THE BLOWER SW (A/C CONTROL ASSEMBLY) IS SELECTED TO MEDIUM (M1, M2, M3) OR HIGH POSITION, THE CURRENT TO
TERMINAL HR OF A/C CONTROL ASSEMBLY FLOWS TO TERMINAL E " GROUND AND TURNS THE HEATER RELAY ON. THEN, THE
CURRENT TO TERMINAL IG+ OF A/C CONTROL ASSEMBLY FLOWS TO TERMINAL BLR " TERMINAL (B)2 OF POWER TRANSISTOR
" TERMINAL (A)1 " GROUND. AS A RESULT, THE CURRENT TO TERMINAL 5 OF HEATER RELAY FLOWS TO TERMINAL 4 "
TERMINAL 2 OF BLOWER MOTOR " TERMINAL 1 " TERMINAL (A)2 OF POWER TRANSISTOR " TERMINAL (A)1 " GROUND AND
BLOWER MOTOR IS ROTATED AT SELECTED SPEED BY THE A/C CONTROL ASSEMBLY CONTROLLING THE CURRENT FLOW FROM
TERMINAL (B)2 OF POWER TRANSISTOR TO TERMINAL (B)1.
* AUTO FUNCTION
WHEN THE AUTO SW IN HEATER CONTROL SW (A/C CONTROL ASSEMBLY) IS SELECTED, THE CURRENT FLOW IS THE SAME AS
ABOVE MENTIONS, BUT THE A/C CONTROL ASSEMBLY DECIDES THE APPROPRIATE AIR FLOW VOLUME ACCORDING TO SET
TEMPERATURE AND THE INPUT SIGNALS FROM EACH SENSOR. BY CONTROLLING THE CURRENT FLOW\
FROM TERMINAL BLR OF
THE A/C CONTROL ASSEMBLY TO TERMINAL (B)2 OF POWER TRANSISTOR " TERMINAL (A)1 " GROUND , THE A/C CONTROL
ASSEMBLY CONTROLS THE BLOWER MOTOR STEPLESSLY.
2. OPERATION OF AIR INLET CONTROL SERVO MOTOR
(SWITCHING FROM FRESH TO RECIRC)
WITH IGNITION SW TURNED ON, THE CURRENT FLOWS FROM HEATER FUSE (10A) TO TERMINAL IG+ OF A/C CONTROL ASSEMBLY
" TERMINAL MREC " TERMINAL 6 OF AIR INLET CONTROL SERVO MOTOR " TERMINAL 2 " TERMINAL MFRS OF A/C CONTROL
ASSEMBLY " TERMINAL E " GROUND , THE MOTOR ROTATES AND THE DAMPER MOVES TO THE RECIRC SIDE. WHEN THE
DAMPER OPERATES WITH THE A/C SW AT RECIRC POSITION, THE DAMPER POSITION SIGNAL IS INPUT FROM TERMINAL 5 OF THE
SERVO MOTOR TO TERMINAL TPI OF THE ECU (BUILT INTO THE A/C CONTROL ASSEMBLY). AS A RESULT, CURRENT TO THE SERVO
MOTOR CIRCUIT IS CUT OFF BY THE ECU, SO THE DAMPER STOPS AT THAT POSITION.
(SWITCHING FROM RECIRC TO FRESH)
WITH IGNITION SW TURNED ON, WHEN THE RECIRC/FRESH SW IS SWITCHED TO THE FRESH SIDE, THE CURRENT FLOWS FROM
TERMINAL IG+ OF A/C CONTROL ASSEMBLY " TERMINAL MFRS " TERMINAL 2 OF AIR INLET CONTROL SERVO MOTOR "
TERMINAL 6 " TERMINAL MREC OF A/C CONTROL ASSEMBLY " TERMINAL E " GROUND , THE MOTOR ROTATES AND THE
DAMPER STOPS AT THAT POSITION.
3. OPERATION OF AIR VENT MODE CONTROL SERVO MOTOR
WITH IGNITION SW TURNED ON, THE CURRENT FLOWS FROM HEATER FUSE (10A) TO TERMINAL IG+ OF A/C CONTROL ASSEMBLY.
(SWITCHING FROM DEF TO FACE)
THE CURRENT FLOWS FROM TERMINAL MFACE OF A/C CONTROL ASSEMBLY " TERMINAL 4 OF AIR VENT CONTROL SERVO
MOTOR " TERMINAL 5 " TERMINAL MDEF OF A/C CONTROL ASSEMBLY " TERMINAL E " GROUND . THE MOTOR ROTATES AND
THE DAMPER MOVES TO THE FACE SIDE. WHEN THE DAMPER OPERATES WITH THE A/C SW AT FACE POSITION, THE DAMPER
POSITION SIGNAL IS INPUT FROM TERMINAL 1 OF THE SERVO MOTOR TO THE TERMINAL TPM OF THE ECU (BUILT INTO THE A/C
CONTROL ASSEMBLY). AS A RESULT, CURRENT TO THE SERVO MOTOR CIRCUIT IS CUT OFF BY THE ECU, SO THE DAMPER STOPS
AT THAT POSITION.
(SWITCHING FROM FACE TO DEF)
THE CURRENT FLOWS FROM TERMINAL DEF OF A/C CONTROL ASSEMBLY " TERMINAL 5 OF AIR VENT CONTROL SERVO MOTOR
" TERMINAL 4 " TERMINAL MFACE OF A/C CONTROL ASSEMBLY " TERMINAL E " GROUND , THE MOTOR ROTATES AND THE
DAMPER STOPS AT THAT POSITION.
SYSTEM OUTLINE
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229
FRESH RECIRC
21
II1
7IE1 13
IQ1
13
IR2
5IR1 2IR11IG1 16 IR1 3 I27
B±Y
R±Y L±RL±Y
L±W
Y
B±R R±L
R±L
BR
B±YG±RLG
GR BR
R± Y
B±Y
R±Y
R±Y
GR
A
8A 7A9B 2A4C6A 3C 5C4A 10 B 23 B11
GR
R±Y
G
G±R B±Y
R±G
L±R L±Y
L±W
Y
B± R
VSV
(
FOR WATER VALVE )
AIR INLET CONTROL
SERVO MOTOR A33
V4
62 5 3 1
BR±W
A1 2 , A 1 3 ,A1 4
A/C CONTROL ASSEMBLY CABM
BLR LV HR A/C IN MGC IG+ WV MREC MFRS RDFGR TPI ST
LG
G±R
BR±W
2 1
NOISE FILTER
( FOR A/C SYSTEM )
N4
R±G R±L
IQ 1
16 IR1 6 Y±G
BR
Y± GBR BR
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