Content .. 973 974 975 976 ..

Lexus SC300 / Lexus SC400. Service manual - part 975

132

ECT AND A/T INDICATOR

: PARTS LOCATION

CODE

SEE PAGE

CODE

SEE PAGE

CODE

SEE PAGE

A21

E 2

S 9

C 3

E 8

S22

C12

E 9

S23

C13

E10

T 2

C14

N 1

T 6

D13

O 5

S 3

E 1

S 4

: RELAY BLOCKS

CODE

SEE PAGE

RELAY BLOCKS (RELAY BLOCK LOCATION)

ENGINE COMPARTMENT LEFT

: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR

CODE

SEE PAGE

JUNCTION BLOCK AND WIRE HARNESS (CONNECTOR LOCATION)

INSTRUMENT PANEL WIRE

COWL WIRE

INSTRUMENT PANEL WIRE

: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS

CODE

SEE PAGE

JOINING WIRE HARNESS AND WIRE HARNESS (CONNECTOR LOCATION)

EB1

ENGINE WIRE AND ENGINE ROOM MAIN WIRE (FRONT SIDE OF R/B NO 2)

EB2

ENGINE WIRE AND ENGINE ROOM MAIN WIRE (FRONT SIDE OF R/B NO. 2)

IG2

INSTRUMENT PANEL WIRE AND COWL WIRE (R/B NO. 5)

IJ1

ENGINE WIRE AND COWL WIRE (RIGHT KICK PANEL)

IJ2

ENGINE WIRE AND COWL WIRE (RIGHT KICK PANEL)

IK1

ENGINE WIRE AND INSTRUMENT PANEL WIRE (RIGHT KICK PANEL)

: GROUND POINTS

CODE

SEE PAGE

GROUND POINTS LOCATION

FRONT SIDE OF LEFT FENDER

REAR SIDE OF CYLINDER HEAD RH

LEFT KICK PANEL

UNDER THE ASHTRAY LH

: SPLICE POINTS

CODE

SEE PAGE

WIRE HARNESS WITH SPLICE POINTS

CODE

SEE PAGE

WIRE HARNESS WITH SPLICE POINTS

E18

ENGINE WIRE

I22

INSTRUMENT PANEL WIRE

E20

ENGINE WIRE

I32

ENGINE WIRE

I19

INSTRUMENT PANEL WIRE

I33

ENGINE WIRE

133

ENGINE CONTROL

THIS SYSTEM UTILIZES AN ECU AND MAINTAINS OVERALL CONTROL OF THE ENGINE, TRANSMISSION AND SO ON. AN OUTLINE OF
THE ENGINE CONTROL IS EXPLAINED HERE.

1. INPUT SIGNALS

(1) WATER TEMP. SIGNAL CIRCUIT

THE WATER TEMP. SENSOR DETECTS THE ENGINE COOLANT TEMP. AND HAS A BUILT–IN THERMISTOR WITH A RESISTANCE
WHICH VARIES ACCORDING TO THE WATER TEMP. THE WATER TEMP. IS INPUT INTO TERMINAL THW OF ENGINE CONTROL
ECU AS A CONTROL SIGNAL.

(2) INTAKE AIR TEMP. SIGNAL CIRCUIT

THE INTAKE AIR TEMP. SENSOR IS INSTALLED IN THE AIR FLOW METER AND DETECTS THE INTAKE AIR TEMP., WHICH IS INPUT
AS A CONTROL SIGNAL TO TERMINAL THA OF ENGINE CONTROL ECU.

(3) OXYGEN SENSOR SIGNAL CIRCUIT

THE OXYGEN DENSITY IN THE EXHAUST EMISSION IS DETECTED AND INPUT AS A CONTROL SIGNAL FROM THE OXYGEN
SENSOR NO. 1 AND NO. 2 TO TERMINALS OX1, OX2 OF THE ECU AND FROM THE OXYGEN SENSOR SUB (FOR CALIFORNIA) TO
TERMINAL OX3 OF THE ECU.

TO STABILIZE DETECTION PERFORMANCE BY THE OXYGEN SENSOR SUB (FOR CALIFORNIA) IS WARMED. THIS HEATER IS
ALSO CONTROLLED BY THE ECU (HT).

(4) RPM SIGNAL CIRCUIT

CRANKSHAFT POSITION IS DETECTED BY THE PICK–UP COIL INSTALLED INSIDE THE DISTRIBUTOR. CRANKSHAFT POSITION
IS INPUT AS A CONTROL SIGNAL TO TERMINALS G1 AND G2 OF THE ECU, AND RPM IS INPUT TO TERMINAL NE.

(5) THROTTLE SIGNAL CIRCUIT

THE THROTTLE POSITION SENSOR DETECTS THE THROTTLE VALVE OPENING ANGLE AS A CONTROL SIGNAL, WHICH IS
INPUT INTO TERMINAL VTA1 OF THE ECU. WHEN THE VALVE IS COMPLETELY CLOSED, THE CONTROL SIGNAL IS INPUT INTO
TERMINAL IDL1.

(6) VEHICLE SPEED CIRCUIT

THE VEHICLE SPEED IS DETECTED BY SPEED SENSOR NO. 1 INSTALLED IN THE TRANSMISSION AND THE SIGNAL IS INPUT TO
TERMINAL SPD OF THE ECU VIA THE COMB. METER.

(7) NEUTRAL START SIGNAL CIRCUIT

THE NEUTRAL START SW DETECTS WHETHER THE SHIFT POSITION IS IN NEUTRAL OR NOT, AND THE SIGNAL IS INPUT INTO
TERMINAL NSW OF THE ECU.

(8) AIRCONDITIONING SW SIGNAL CIRCUIT

THE OPERATING VOLTAGE OF THE A/C MAGNETIC CLUTCH IS DETECTED AND THE SIGNAL IS INPUT INTO TERMINAL ACMG OF
ECU AS A CONTROL SIGNAL.

(9) BATTERY SIGNAL CIRCUIT

VOLTAGE IS CONSTANTLY APPLIED TO TERMINAL BATT OF THE ECU. WITH THE IGNITION SW TURNED ON, THE VOLTAGE FOR
ECU START–UP POWER SUPPLY IS APPLIED TO TERMINALS +B AND +B1 OF ECU VIA EFI MAIN RELAY.

THE CURRENT FLOWING THROUGH THE IGN FUSE FLOWS TO TERMINAL IGSW OF THE ECU.

(10) INTAKE AIR VOLUME SIGNAL CIRCUIT

INTAKE AIR VOLUME IS DETECTED BY THE AIR FLOW METER AND THE SIGNAL IS INPUT TO TERMINAL KS OF THE ECU AS A
CONTROL SIGNAL.

(11) STOP LIGHT SW SIGNAL CIRCUIT

THE STOP LIGHT SW IS USED TO DETECT WHETHER OR NOT THE VEHICLE IS BRAKING AND THE SIGNAL IS INPUT INTO
TERMINAL STP OF THE ECU AS A CONTROL SIGNAL.

(12) STA SIGNAL CIRCUIT

TO CONFIRM WHETHER THE ENGINE IS CRANKING, THE VOLTAGE APPLIED TO THE STARTER MOTOR DURING CRANKING IS
DETECTED AND THE SIGNAL IS INPUT INTO TERMINAL STA OF THE ECU AS A CONTROL SIGNAL.

(13) ENGINE KNOCK SIGNAL CIRCUIT

ENGINE KNOCKING IS DETECTED BY KNOCK SENSOR NO. 1 AND NO. 2 AND THE SIGNAL IS INPUT INTO TERMINALS KNK1 AND
KNK2 AS A CONTROL SIGNAL.

SYSTEM OUTLINE

2. CONTROL SYSTEM

* EFI (ELECTRONIC FUEL INJECTION) SYSTEM

THE EFI SYSTEM MONITORS THE ENGINE CONDITION THROUGH THE SIGNALS INPUT FROM EACH SENSOR (INPUT SIGNALS
FROM (1) TO (13) ETC.) TO THE ECU. THE BEST FUEL INJECTION TIMING IS DECIDED BASED ON THIS DATA AND THE PROGRAM
MEMORIZED BY THE ECU, AND THE CONTROL SIGNAL IS OUTPUT TO TERMINALS #10, #20, #30, #40, #50 AND #60 OF THE ECU TO
OPERATE THE INJECTOR. (INJECT THE FUEL). THE EFI SYSTEM PRODUCES CONTROL OF FUEL INJECTION OPERATION BY THE
ECU IN RESPONSE TO THE DRIVING CONDITIONS.

* ESA (ELECTRONIC SPARK ADVANCE) SYSTEM

THE ESA SYSTEM MONITORS THE ENGINE CONDITION THROUGH THE SIGNALS INPUT TO THE ECU FROM EACH SENSOR (INPUT
SIGNALS FROM (1), (2), (4) TO (13) ETC.). THE BEST IGNITION TIMING IS DECIDED ACCORDING TO THIS DATA AND THE
MEMORIZED DATA IN THE ECU AND THE CONTROL SIGNAL IS OUTPUT TO TERMINAL IGT THIS SIGNAL CONTROLS THE IGNITER
TO PROVIDE THE BEST IGNITION TIMING FOR THE DRIVING CONDITIONS.

* OXYGEN SENSOR HEATER CONTROL SYSTEM (USA SPEC.)

THE OXYGEN SENSOR HEATER CONTROL SYSTEM TURNS THE HEATER ON WHEN THE INTAKE AIR VOLUME IS LOW (TEMP. OF
EXHAUST EMISSIONS IS LOW), AND WARMS UP THE OXYGEN SENSOR TO IMPROVE DETECTION PERFORMANCE OF THE
SENSOR.

THE ECU EVALUATES THE SIGNALS FROM EACH SENSOR (INPUT SIGNALS FROM (1), (2), (4), (9) TO (11) ETC.,) AND OUTPUTS
CURRENT TO TERMINAL HT TO CONTROL THE HEATER.

* ISC (IDLE SPEED CONTROL) SYSTEM

THE ISC SYSTEM (STEP MOTOR TYPE) INCREASES THE RPM AND PROVIDES IDLING STABILITY FOR FAST IDLE–UP WHEN THE
ENGINE IS COLD, AND WHEN THE IDLE SPEED HAS DROPPED DUE TO ELECTRICAL LOAD AND SO ON. THE ECU EVALUATES
THE SIGNALS FROM EACH SENSOR (INPUT SIGNALS FROM (1), (4), (5), (8), (9), (11) ETC.), OUTPUTS CURRENT TO TERMINAL ISC1,
ISC2, ISC3 AND ISC4 TO CONTROL ISC VALVE.

* EGR CONTROL SYSTEM

THE EGR CONTROL SYSTEM DETECTS THE SIGNAL FROM EACH SENSOR (INPUT SIGNALS FROM (1), (4), (9), (10) ETC.), AND
OUTPUTS CURRENT TO TERMINAL EGR TO CONTROL THE EGR VALVE.

* FUEL PUMP CONTROL SYSTEM

THE COMPUTER OUTPUTS CURRENT TO TERMINAL FPC AND CONTROLS THE FUEL PUMP ECU AND FUEL PUMP DRIVE SPEED
IN RESPONSE TO CONDITIONS.

* ACIS (ACOUSTIC CONTROL INDUCTION SYSTEM)

ACIS INCLUDES A VALVE IN THE BULKHEAD SEPARATING THE SURGE TANK INTO TWO PARTS. THIS VALE IS OPENED AND
CLOSED IN ACCORDANCE WITH THE DRIVING CONDITIONS TO CONTROL THE INTAKE MANIFOLD LENGTH IN TWO STAGES FOR
INCREASED ENGINE OUTPUT IN ALL RANGES FROM LOW TO HIGH SPEEDS.

THE ECU JUDGES THE VEHICLE SPEED BY THE SIGNALS ((4), (5)) FROM EACH SENSOR AND OUTPUTS SIGNALS TO THE
TERMINAL ACIS TO CONTROL THE VSV (FOR OPENING AND CLOSING THE INTAKE CONTROL VALVE).

3. DIAGNOSIS SYSTEM

WITH THE DIAGNOSIS SYSTEM, WHEN THERE IS A MALFUNCTION IN THE ECU SIGNAL SYSTEM, THE MALFUNCTIONING SYSTEM IS
RECORDED IN THE MEMORY. THE MALFUNCTIONING SYSTEM CAN BE FOUND BY READING THE CODE DISPLAYED BY THE
CHECKING ENGINE WARNING LIGHT.

4. FAIL–SAFE SYSTEM

WHEN A MALFUNCTION HAS OCCURRED IN ANY SYSTEM, IF THERE IS A POSSIBILITY OF ENGINE TROUBLE BEING CAUSED BY
CONTINUED CONTROL BASED ON THE SIGNALS FROM THAT SYSTEM, THE FAIL–SAFE SYSTEM EITHER CONTROLS THE SYSTEM
BY USING DATA (STANDARD VALUES) RECORDED IN THE ECU MEMORY OR ELSE STOPS THE ENGINE.

NOTE: THE SPECIFICATION DESCRIPTIONS “USA SPEC.” AND “EXC. USA SPEC.” USED IN THIS SECTION INDICATE THE
FOLLOWING SPECIFICATIONS.

USA SPEC. : USA (50 STATES) SPECIFICATIONS

EXC. USA SPEC. : USA (EXCEPT CALIFORNIA) AND CANADIAN SPECIFICATIONS.

Content .. 973 974 975 976 ..