Toyota COMPUTER-CONTROLLED SYSTEM Training Manual

training manual

VOLUME 1 STEP 3 /

TCCS
(TOYOTA COMPUTER­CONTROLLED SYSTEM)

FOREWOR

D

This Training

Manual has been prepared

distributors and dealers

. This manual,

for the

"TCCS (Toyota Computer-Controlled System)", is Volume 1 of

use of technicians

employed by Toyota's

the thirteen Training Manuals which constitute Step 3 of the program of skills which all Toyota New
TEAM*

technicians should master

accompanying

The titles

VOL

of the New

.

1

TCCS (Toyota Computer-Controlled System)

2

Turbocharger & Supercharger

3

Diesel Injection Pump

4

ECT (

5

Full-Time 4WD

6

TEMS & Air Suspension

ABS & Traction Control Syste

7

Instruction Guide

TEAM Step

TRAINING MANUALS

Electronically-Controlled Transmission)

. It should also be used by the instructor in conjunction

.

3 Training Manuals are as follows

VOL

.

NVH (Noise, Vibration & Harshness

8

Fundamentals of Electronic

9

CCS

10

1 1

Car Audio Syste

12

Automatic Air Conditioning Syste

13

SRS Airbag & Seat Belt Pretensione

m

:

TRAINING MANUAL

(Cruise Control System

m

S

s

)

It is not enough just to "know" or "understand" - you need to master each task so that you can do

. For this reason, theory and practice have been combined in this Training Manual

it

. The top of each
page is marked either with a Q symbol to indicate that it is a Theory page or a® symbol to indicate
that it is a Practice page

.

overseas

with the

)

m

r

Note that in regards to inspection and other procedures mentioned in the Practice section, this

Training Manual contains only the main points to be learned

Manual(s) for details

.

; please refer to the relevant Repair

The following notations often occur in this manual, with the meanings as explained

CAUTION

NOTICE

NOTE

REFERENCE

A potentially hazardous situation which could result in injury to people may occur i

instructions are not followed

Damage to the vehicle or components may occur if instructions are not followed

Notes or comments not included under the above two headings

Information not required to pass the TEAM certification, but which may be useful t
instructors and to trainess who wish to gain a deeper knowledge of the subject

.

.

:

f

.

o

.

ry'

*TEAM:TEAM stands
according to the technician's technical level
level in a systematic manner so as to help them achieve the skills and efficiency of skilled technicians in the sho

for 'Technical Education for Automotive Maste

. This program makes it possible for technicians to receive the appropriate training for their

, which is a training program divided into three steps

rt

est possible time

.

This Training Manual explains the TCCS

representative engines other than the
mechanisms not found" on the 4A-FE engine
possible have been included

All

information contained in this manual is the most up-to-date at the time of publication

.

we reserve the right to make changes without prior notice

engine control system based on the 4A-FE engine . However,

4A-FE

engine have sometimes been selected to explain

. In this way, explanations of as many mechanisms as

.

. However,

TOYOTA MOTOR CORPORATIO

N

©1997 TOYOTA
All rights reserved

duced or copied, in whole or in part, without the
written permission of Toyota Motor Corporation

MOTOR CORPORATION

. This book may not be repro-

.

TABLE OF CONTENT

S

Page

ABBREVIATIONS AND ECU TERMINAL SYMBOL

.

ABBREVIATIONS....

ECU TERMINAL SYMBOLS

OUTLINE OF TCC

WHAT IS TCCS?
HISTORY OF TCCS ENGINE CONTROL

SYSTEM

SYSTEM DESCRIPTION

. Functions of engine control system..

1

2

. Construction

system.......... . . . ... . . ..... . ..... . . ..... . ..... 10

. Engine control system diagram

3

ELECTRONIC CONTROL SYSTE

GENERAL
POWER CIRCUITRY

1

. Engine without stepper motor typ

ISC valve

2

. Engine with stepper motor typ

ISC valve.......

VC CIRCUITRY.... . . ...

GROUND CIRCUITRY

MANIFOLD PRESSURE SENSO

(VACUUM

AIR FLOW METER

1

. Vane type
. Optical Karman vortex type

2

. Hot-wire type

3

THROTTLE POSITION SENSOR

1

. On-off type
. Linear type

2

G AND NE SIGNAL GENERATORS

1

. In-distributor type

2

. Cam position sensor type....

3

. Separate type

WATER TEMPERATURE SENSOR

INTAKE AIR TEMPERATURE
OXYGEN SENSOR (02 SENSOR)

1

. Zirconia element type

2

. Titania element type

LEAN MIXTURE SENSOR

S

. . .

.....

. . ..... . . . ... . . ... . . . ..... . . ..... . ....6

. . ..... . . ... . . . .....

. ..... . ..... . . . . . . . . .

SENSOR)....

. . ..... . ..... . ..... . . ..... . ..... . .

. . .

. . ........... . ..... . . ....... . ... . ... 22

. . ... . . . ..... . ..... . . ... . ...

. . . ... . ....... . . ... . . . ... 1

. . . . .

. ... . . ..... . . .

. . . . ... . . . ..... . ..... . . .........

. . . .

. .

. . . ....... . . . . . . . . .

of engine contro

M

. ..... . ..... . . ...........

. ... . . . .....

...

.

. . . ........... . . ..... . ..... .

. . . ..... . ..... . . . . ... . ....... 16

. ..... . . ...........

.

. . ..... . ... . . . . ..... . . . ... .

. . . . . ......... . . .

. ..... . ..... . . . . . . . . ..... . ..... . .

. .

. . ............ . . ... . . . .....

. . . . . ... . ....... . . ..... . ... 24

.

. . ..... . . . ... . . ... . . . ..... .

. .

. . . ...

l

... . ..... 1

e

... . . . ... . . . . . . .

e

R

. .

. . . . . . ..... . .

. ..... . . . . . . . . .

... . ... 2

.

. . . .......

.

. . . ... 27

. . . .

.

. . . ..... . ...

SENSOR.. .

. . . .......

......... . . ..... . .

....... ..... . ..... . .....

..... . . . . ... . ..... . ..... 33

. 5

. 7

. 8

. 13
. 15

. 15

. 16

. 16

. . . .

. 18
. 18
. 21

. 21-

. 22

. 24

.

. . .

. 2
. 30

.

...

. 30­. 30-1

17

30

.32

Page

. . . . ...

. 3

. .

. .

. . . .

. .

...

.

. ... 44

. ...

. .

. .

. 34
. 34

. 35

. 3

. 38

. 38

. 39

. 40
. 40
. 41

. 42
. 42

. 42

. 43
. 44
. 44

. 45
. 45
. 4
. 45

. 46

. 46

. 47

. 47

. 47

. 49
. 52
. 52

4

6

5

8

S

2

2

1

3

8

1

VEHICLE SPEED

1

. Reed switch

2

. Photocoupler
. Electromagnetic pickup type

3
4

. MRE type

STA SIGNAL.. . ..... . . ... .

NSW SIGNAL
A/C SIGNAL
ELECTRICAL LOAD SIGNAL
FUEL CONTROL SWITCH O

CONNECTOR..

EGR GAS TEMPERATURE SENSOR

VARIABLE RESISTOR

KICK-DOWN SWITCH
WATER TEMPERATURE SWITCH
CLUTCH SWITCH
KNOCK SENSOR
HAC SENSOR

VAPOR PRESSURE
TURBOCHARGING
STOP LAMP SWITCH

OIL PRESSURE

COMMUNICATIONS SIGNALS

1

. Throttle

2

. Throttle

TRC system

3

. Cruise control syste

communications signal

4. TRC system

5

. ABS communications signal

6

. Intercooler system warning signal

7

. EHPS system

signal

8

. Engine speed signal

9

. Engine immobiliser syste

communications

DIAGNOSTIC

EFI (ELECTRONIC FUEL INJECTION

GENERAL...... . ... ... . ..... . ..... . ....... ...

TYPES OF EFI

1

. D-type EFI..

SENSOR....

type

type

. ... . . . ..... . ..... . .

. . ..... . . .

. . . . ..... . . .

. . . . . . . . ... . . . ... . . ... . . . ...........

opening angle signals
opening angle signals fo

. ... . . . ..... . . . ...

. .
. .

. . . ...

. ..... . ................. . . .

. . . ... . . . . ... . . ..... . .......

SENSOR

PRESSURE

SWITCH

. . ... . ... . . . .......

communications signal.. 46

communication

TERMINAL(S)

. ..... . . ... . . . ...............

. . . ... . . . . . . . . . ... . . .

. . ..... . . .

. . . . ........... . ...

. . ........... . .....

. . ... .

. . ..... . ..... . . . ... . . . ... .

.

. . ............. . ..... .

. . . .

. . . ..... . ..... . ....... 39

. . . . .

.

. .

R

. . . ..... . ..... . . . ... . . . . . . . .

. . . . . . . . . ................. . .

. . ... . . . . . . . . . . ... . . . ..... . .

. . . . . ..... . ..... . .

. ... . .......

. . . ..... . .

m

. . . ..... . ..... . ..... 46

. . . . . . . . ... . . . ..... . .....

...

. . . . ... . . . ... . . .

signal

. . . . . . . . ......•.••••• 4

. .

. . . . ...

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......... . .

. ... . . . . . . . . .

. .

. . . ..... . ..... .

. . . . ... . .

. .

. . . ..... . .

. .

.....

SENSOR

..... . ..... . . . .

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... . ..... . ...

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...

. . ..... . ..... 45

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DIAGNOSTIC CODES

FAIL-SAFE FUNCTIO

FAIL-SAFE FUNCTION

.

. . ..... . . ..... . ..... . . . ... .

N

. . ..... . . ... . . . ... . ......... 14

Page

. 13

8

5

APPENDIX

ENGINE CONTROL SYSTE

SPECFICATION CHART

M

. . . . ...

. . . . ..... . . . . .

..

Pag

. 18

e

8

BACK-UP FUNCTIO

BACK-UP FUNCTION

TROUBLESHOOTIN

GENERAL
HOW TO CARRY OU

TROUBLESHOOTING
PRE-DIAGNOSTIC QUESTIONING
SYMPTOM CHART

® CHECKING AND CLEARING DIAGNOSTIC

CODE

"CHECK ENGINE" LAMP CHECK
OUTPUT OF DIAGNOSTIC CODE

1

2

CLEARING DIAGNOSTIC CODE

IS

SYMPTOM SIMULATION

® BASIC INSPECTION

..... . ..... . . ..... . . . ... . . . . . . . . ... . . . ..... . .

S

. Normal mode..

. Test mode

N

.

. . ... . . . . ..... . ..... . . . . . . . .

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T

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...

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. . ..... . ..... . . . . . . . . ..... . ..... . . .

... . . . ...

.

. . . ..... . . . ... . . ... . . . ...

... . ..... . . ... . . . ..... . . . ... . . . ... 167

. . ...

.

. .

. .

. 14

7

. 149
. 150

. 152

. 1

5

4

.

. 159

. 15

9

.

. 161

2

. 16

. 163

DELETED FOR NEW EDITIO

. . . ... . . . . ..... . . . .

. 118, 119, 125, 126, 141 to 144,

166 and 174

N

INSPECTION AND ADJUSTMEN

GENERAL
IDLE SPEED AND IDLE MIXTURE
MANIFOLD PRESSURE SENSO

(VACUUM SENSOR)

THROTTLE POSITION SENSO

(LINEAR TYPE) AND THROTTL

BODY
DISTRIBUTOR (G AND NE SIGNALS)
INTAKE AIR TEMPERATURE
FEEDBACK CORRECTION

Models with oxygen senso

Models with

VARIABLE RESISTOR

ISC VALV

(DUTY-CONTROL ACV TYPE)

.

. . ... . . . ... . . . . ... . . . ..... . . . . . . . . ... . . . ...

. . . . . . . . . ..... . ..... . ... .

. . . ... . . . ... . . . . ... . . . ..... . . . . . . . . ... . . . ...

.

(02 sensor)

. . . ..... . ..... . . ... . . . ... . . . ....... 182

lean mixture sensor

. . ... . . ....... . . . ... . . ... . . .

E

T

R

R

SENSOR

. . . . ..... . ..... . . .

r

. . . . . . . . ...

E

.

. . .....

. . . . . .

.

.

. .

. . . . ..... .

..... . . . ... . .

. 171

.

.

. 172

.

. 175

.

. 177
. 180
. 181
. 182

. 183
. 184

. 186

ABBREVIATIONS AND ECU TERMINAL SYMBOLS

- Abbreviations

4

ABBREVIATIONS AND ECU TERMINAL SYMBOL

ABBREVIATION

ABS Anti-Lock Brake System
ABV Air Bypass Valv

AC Alternating Current
A/C Air Conditione
ACIS Acoustic Control Induction System
ACV Air Control Valv
Al Air Injection
AS Air Suctio
ASV Air Switching Valv
A/T Automatic Transmission

BTDC

CA Crankshaft Angl
CALIF Californi

CCS Cruise Control System
CO Carbon Monoxid

DIS Direct Ignition System
DLI Distributorless Ignition

EC European Countrie
ECT Electronically-Controlled Transmission
ECU Electronic Control Uni
EFI Electronic Fuel Injection

EGR Exhaust

EHPS Electro-Hydraulic Power Steering

ESA Electronic Spark Advanc

FED

. Federal

GEN

. General

HAC High-Altitude Compensation
HC Hydrocarbo
HIC Hybrid Integrated Circui
IIA Integrated Ignition Assembly
ISC Idle Speed Contro
LED Light Emitting Diode
LS Lean Mixture Senso

MRE Magnetic
M/T Manual
NOx Oxides

OC Oxidation Catalyst
OD Overdrive
02 Oxygen

PS Power Steering

Before Top Dead Center

S

e

r

e

n

e

e

a

e

s

t

Gas Recirculatio

Countrie

Resistance Element

Transmissio

of Nitrogen

s

n

l

r

n

SCV Swirl Control Valve

SST Special Service Tool

SW Switc
TCCS Toyota Computer-Controlled System
TDC Top Dead Cente
TDCL

*1

TEMS Toyota Electronically-Modulated

Tr Transisto

TRC*2 Traction Contro

T-VIS Toyota-Variable Induction System

TWC Three-Way Catalys

. United State

U

.S

VSV Vacuum Switching Valve

w/ Wit

w/o Withou

4WD

In vehicles sold at Lexus dealers in the U
Canada, this is called the "Total Diagnostic

n

e

t

Communication Link"
countries, and in Toyotas sold at Toyota dealers
in the U.S. and Canada, it is called the "Toyota

Diagnostic Communication Link"
manual, it is called the "Toyota Diagnostic

Communication Link"

the U.S. and Canada, this is abbreviated to

*2 In

TRAC

.

/--

Abbreviations in accordance with SAE terms
are used for vehicles sold in the U

Canada
ferences between SAE terms and Toyota

terms

Example
ECM Engine Control Module

(=

c

iw

1

. Refer to the Repair Manual for dif-

.

Engine ECU

h

r

Toyota Diagnostic Communication

Link or Total Diagnostic
Communication Lin

Suspension

r

s

h

t

4-Wheel-Driv

:

)

k

l

t

e

. In Toyotas sold in other

.

ECT Engine Coolant Temperature

(= THW)

S

.S

. and

. In this

.S.A. and

1

ABBREVIATIONS AND ECU TERMINAL SYMBOLS

- ECU Terminal Symbol

s

ECU TERMINAL SYMBOL

SYMBOL MEANING
ABS Anti-Lock Brake Syste
ACC1 Acceleration Signal No

Throttle Position Sensor)

ACC2 Acceleration Signal No

Throttle Position Sensor)

A/C Air Conditione

ACMG

ACT Air Conditioner Cut-Of
Al Air Injection
AS Air Suctio
A/D Auto Drive (Cruise Control System)
+B Ba
+B1 Ba

BATT Ba
BF Ba

BRK Brake

DFG Defogge
E01 Ea

E02 Ea
E1 Ea

E2 Ea
ECT Electronically-Controlled Transmission

ELS Electrical Load Signa
EGR Exhaust Gas Recirculation
FC Fuel Pump Contro
FP Fuel Pump Control Relay
FPU Fuel Pressure-U
FS Fail-Safe Rela

G Group (Crankshaft Angle Signal
G1 Group No
G2 Group No
G- Group Minus (-

HAC High-Altitude Compensatio
HT Heater (for Oxygen Sensor or Lean

IDL Idle Switch (in Throttle Position

IGDA Ignition Distribution Signal A

IGDB Ignition

IGF Ignition Failure (Confirmation) Signal
IGSW Ignition Switc
IGT Ignition Timing Signal

Air Conditioner Magnetic Clutch

tter

y

ttery

No

tter

y

ttery

Fail Safe

h No

rt
rt

h No
h No

rt

h No

rt

Mixture Sensor

Sensor

)

r

n

. 1

r

. 01 (Ground)
. 02 (Ground)

. 1 (Ground)
. 2 (Ground

.

1 (Crankshaft

.

2 (Crankshaft

Distribution

)

l

p

y

)

)

h

S

m

. 1(from

.

2 (fro

f

l

Angle Signal)

Angle Signal)

n

Signal

SYMBOL MEANIN

ISC1 Idle Speed Control Signal No
ISC2 Idle Speed Control Signal No

ISC3 Idle Speed Control Signal No

m

)

B

ISC4 Idle Speed Control Signal No
KD Kick-Dow

KNK Knock Sensor
KS Karman Signa

L7 Throttle Valve Opening
L2 Throttle Valve Opening

L3 Throttle Valve

LP Lam
LS Lean Mixture Sensor
LSW Lean Burn Switch
M-REL EFI Main Rela
N/C Neutral
NE Number of Engine Revolutions

NE- Number of Engine Revolutions

NEO Number of Engine

No

.10

No

.20

NSW Neutral Sta

OX Oxygen Senso

OX + Oxygen Sensor ~+

OIL Oil Pressur

OD Overdrive
PS Power Steerin
PSW Power Switch

PIM Pressure, Intake Manifol
R-P Regular or Premium Gasoline Signal

RSC Rota
RSO Rota
SCV Swirl Control Valv
SPD Vehicle Spee
SP2 Vehicle Speed No
SP2- Vehicle Speed No
STA Sta

STJ Cold

p

Clutch Switc

Signa

l

Signal Minus (-

Signal Outpu

(for Injectors)
(for Injectors

Sensor

)

ry

Solenoid Valve Close
Solenoid Valve Open

ry

rter

StartInjecto

G

n

l

Opening Signal No

y

h

)

Revolutions

t

)

rt Switch

r

e

g

(in Throttle Position

e

d

.

2

. 2 Minus (-)

r

. 1
. 2
. 3
. 4

Signal No
Signal No

d

d

. 1
. 2
. 3

2

ABBREVIATIONS AND ECU TERMINAL SYMBOLS

SYMBOL MEANING
STP Stop Lamp Switch

T Test Termina

l
TE1 Test Terminal, Engine No
TE2 Test Terminal, Engine No
THA Thermo, Intake Ai

r
THG Thermo, Exhaust Gas
THW Thermo, Wate
TR Traction Contro

r

l
T-VIS Toyota-Variable Induction System
TSW Water Temperature Switc

VAF Voltage, Air-Fuel Ratio Control
VB Voltage, Batter

y
VC Voltage, Constant
VF Voltage, Feedbac

k

VG Voltage, Gram Intake Air
V-ISC VSV Type Idle Speed Control
VS Voltage, Slide Signa

l

VSH Voltage, Sub-Throttle Angle
VTA Voltage, Throttle Angle

VTH Voltage, Throttle Angl

e

W "CHECK ENGINE" Warning Lamp
WIN Warning Lamp, Intercooler

. 1
. 2

h

- ECU Terminal Symbol

F4$

s

3

b

OW3W

OUTLINE OF TCCS

- What is TCCS

?

®

OUTLINE OF TCC

WHAT IS

"TCCS" (Toyota Computer-Controlled System) is

the general name for a system which exercises

comprehensive and highly precise control of the
engine, drive train, brake system, and other
systems by means of an ECU* (electronic control
unit), at the heart of which is a microcomputer
Previously, TCCS was used as an engine control

system for only EFI (electronic fuel injection),
ESA (electronic spark advance), ISC (idle speed
control), diagnosis, etc

Later, control systems utilizing other separate
ECUs were developed and adopted for the
control of systems other than the engine also
Currently, the term "TCCS" has come to mean a
comprehensive control system which incorpo-

TCCS

?

.

S

rates control systems controlled by various ECUs

to ensure basic vehicle performance, not only

running, turning and stopping
*At Toyota, a computer which controls each

type of system is called an "ECU"

.

REFERENCE

On some vehicle models,
ECU, called
engine control is called the

this case

not have its own separate

.

the ECU for

called the "Engine

the "ECT ECU"

.) On models in which

engine control, which is then

and ECT ECU"

.

.

the ECT

ECU, the ECT uses

has its own

. (The ECU for

"Engine ECU" in

the ECT does

.

CONCEPTUAL DIAGRAM OF TCC

This manual explains the TCCS type engine

control system

systems (ECT, ABS, TEMS, etc
the training manual for each individual system

. For details concerning other

.), please refer to

.

TCC

S

S

In addition, this manual assumes that you have
mastered the contents of the manual for Step 2,
vol.5 (EFI).If you have not, please read that
manual carefully before beginning this one

OHP

1

.

5

11

OUTLINE OF

TCCS - History of TCCS Engine Control Syste

m

HISTORY OF TCCS ENGINE CONTROL SYSTE

The ECU used for conventional EFI in export
models beginning in 1979 was the analog circuit
type, which controlled the injection volume
based on the time required for a capacitor to be
charged and discharged

.

The microcomputer-controlled type was added
beginning in 1981

CYL

.

ARR

.

K series(4K-E)
E series

A series(4A-GE, 4AG-ZE

S series(2S-E

L4

R series(22R-E

. That was the beginning of the

ENGINE MODELS

(

3E-E) [2E-E, 4E-FE, 5E-FE

)

[4A-FE, 5A-FE, 7A-FE

]

)

(1 S-i,

1S-E,

2S-E)13S-FE, 5S-FE

3S-GE, 3S-GTE

)

(22R-TE) [22R-E]

]

]

,

engine

control system using

however, the TCCS engine

only

controls

ignition timing
speed, and other such advanced systems
well as the diagnostic,

functions

.

1980 1985 1990 199

--

~

M

~

EFI, but

; ISC, which

control

also

ESA, which controls

controls the idle

fail-safe,

TCCS

. Now

system not

and back-up

5

,

; as

Y series(3Y-E

RZ series [1RZ-E, 2RZ-E, 2RZ-FE, 3RZ-FE

TZ series [2TZ-FE, 2TZ-FZE]

G series(1G-E)[1G-FE

M series (4M-E, 5M-E, 5M-GE

L6

JZ series

F series(3F-E)
FZ series [ 1 FZ-FE
VZ series(2VZ-FE)[3VZ-E, 3VZ-FE, 5VZ-FE

)

[4Y-E

]

(1G-GE)

(5M-GE, 6M-GE, 7M-GE, 7M-GTE

[2JZ-GE,

V6

MZ series [1 MZ-FE

V8

UZ series [1UZ-FE

INTAKE AIR SENSING DEVICE

Vane type air flow meter
Manifold pressure (vacuum) senso

]

2JZ-GTE]

]

]

]

1

~

-----

~

)

)

~

~

]

S

r

~

-

Optical Karman vortex type air flow mete
Hot-wire type mass air flow meter

1

: No longer in production models
: Current product models

I I

6

r

-

---

~

: EFI (EFI control only

TCCS

(EFI, ESA, ISC, Diagnosis,

)

etc

)

OUTLINE OF TCCS

- System Descriptio

n

SYSTEM DESCRIPTIO

N

The functions of the engine control system In addition, there are auxiliary engine control
include EFI, ESA, and ISC, which control basic devices on the engine, such as the OD cut-off con­engine performance
which is useful when repairs are made
safe and back-up functions, which operate when ECU
any of these control systems malfunction

; a diagnostic function, trol system, intake air control system, and others

; and fail- These functions

are all

controlled by the Engine

.

.

Fuel pum

Manifold pressure

sensor

p

"E

Water temp

Knock senso

Distributor

and

ignite

. sensor

r

,

(

r

Circuit opening relay

Engine EC

Variable resistor

Check connecto

Idle speed control
valv

e

Intake air temp

. senso

r

Ignition switc

U

'

r

.

h

"Applicable only to General Country specification vehicles without oxygen sensor

LAYOUT OF

(COROLLA

ENGINE CONTROL SYSTEM COMPONENTS

4A-FE ENGINE FOR EUROPE Apr

.

., 1992)

7

0

1

. FUNCTIONS OF ENGINE CONTROL SYSTE

OUTLINE OF

TCCS - System Descriptio

M

n

EFI (ELECTRONIC FUEL INJECTION

An electric fuel pump supplies sufficient fuel,

under a constant pressure, to the injectors

These injectors inject a metered quantity of fuel

into the intake manifold in accordance with
signals from the Engine ECU

.

)

The Engine ECU receives signals from various

sensors indicating changing engine operating
conditions such as

• Manifold pressure (PIM) or
(VS, KS or VG

:

intake air volume

)

• Crankshaft angle (G)

• Engine speed (NE

)

• Acceleration/deceleration (VTA)

• Coolant

• Intake air

etc

.

temperature (THW

temperature (THA)

)

ESA (ELECTRONIC SPARK ADVANCE

)

The Engine ECU is programmed with data that

.

will ensure optimal ignition timing under any
and all operating conditions. Based on this data,
and on data provided by the sensors that

monitor various engine operating conditions,
such as those shown below, the Engine ECU
sends IGT (ignition timing) signals to the igniter
to trigger the spark at precisely the right instant

• Crankshaft angle (G

• Engine speed (NE

)

)

.

• Manifold pressure(PIM) or intake air volume

(VS, KS or VG

)

• Coolant temperature (THW)

etc

.

Igniter and ignition coi

l

These signals are utilized by the Engine ECU to
determine the injection duration necessary for

the optimal air-fuel ratio to suit the present
engine running conditions

Fue

l

.

+

Engine

EC

Sensor

U

s

OHP 3

Sensor

s

OHP

3

8

OUTLINE OF

TCCS - System Descriptio

n

ISC (IDLE SPEED
The Engine

CONTROL

ECU is

)

programmed with target

engine speed values to respond to different
engine conditions such as

:

• Coolant temperature (THW)

• Air conditioner
etc

.

on/off (A/C)

Sensors transmit signals to the Engine ECU,
which, by means of the ISC valve, controls the
flow of air through the throttle valve bypass and
adjusts the idle speed to the target value

ISC valve

DIAGNOSTIC FUNCTIO

The Engine ECU is constantly monitoring the

signals that are input to it from the various
sensors
input signals, the Engine ECU stores data on the
malfunction in its memory and lights the

"CHECK ENGINE"

displays the malfunction
ENGINE" lamp, displaying on a tester* or output-

ting a voltage signal

. If it detects any malfunctions in the

* OBD-II scan tool or

N

lamp

. When necessary, it

by lighting the "CHECK

.

TOYOTA

hand-held teste

r

.

"CHECK ENGINE" lamp

OHP

4

Sensor

OHP 4

FAIL-SAFE FUNCTIO

N

If the signals input to the Engine ECU are

s

abnormal, the Engine ECU switches to standard
values stored in its internal memory to control
the engine

. This makes it possible to control the

engine so as to continue more-or-less normal
vehicle operation

BACK-UP FUNCTIO

.

N

Even if the Engine ECU itself becomes partially
inoperative, the back-up function can continue to

execute fuel injection and ignition timing
control

. This makes it possible to control the

engine so as to continue more-or-less normal
vehicle operation

OTHER CONTROL SYSTEM

.

S

In some engines, the OD cut-off control system,
intake air control system, and some other aux­iliary systems are also controlled by the Engine

ECU

.

9

®

2

. CONSTRUCTION OF ENGINE CONTROL SYSTE

OUTLINE OF

TCCS - System Descriptio

M

n

BLOCK DIAGRA

M

The engine control system can be broadly The sensors and actuators which form the basis

divided into three groups
Engine ECU and the actuators

SENSOR

MANIFOLD PRESSURE I I I I EF

SENSOR

AIR FLOW METER*2

----------------------------

• Crankshaft angle signa

• Engine speed signa

WATER TEMP

INTAKE AIR TEMP

THROTTLE

• Idling signa

• Throttle position signa

IGNITION SWITCH

• Starting signa

VEHICLE SPEED SENSO

(D-TYPE EFI

(L-TYPE EFI

DISTRIBUTOR

POSITION SENSO

l

(ST TERMINAL

l

: the sensors, the of an engine control system used in an engine

. with an oxygen sensor are shown below

S

)

l

. SENSO

. SENSO

)

)

l

R

R

R

l

R

PIM ~10

VS, KS

or VG

TH

TH

ID L

T

ST

SP

G

N

E

W

A

A

A

D

ENGINE IRSO

ECU

#20

IG

T
F

IG

IS

C

RSC

H T

NO
NO

IDLE SPEED

I

OXYGEN SENSOR HEATER

OXYGEN SENSOR HEATE

ACTUATORS*

.1 AND 3 INJECTOR
.2 AND 4 INJECTOR

IGNITION COI

DISTRIBUTO

SPARK PLUG

CONTRO

I

ES

A

IGNITE

R

i

L

i

R

t

S

IS

C

CONTROL VALV

L

.

'

S
S

E

R

10

OXYGEN SENSO

VARIABLE

NEUTRAL START SWITC

RESISTOR-

TAILLIGHT

DEFOGGER RELAY

AIR CONDITIONE

KNOCK

CHECK CONNECTOR

*

1

Actuators only related profoundly to the engine control are shown here

*

2

Although a D-type EFI is shown in the above figure and a L-type EFI sensor is also shown for reference

*3

Applicable only to General Country specification vehicles without oxygen sensor

SENSO

&

R

R

R

3

S

H

COROLLA

OX

VA

F

NS

W

EL

S

A/

C

KN

K

T

E

TE

BATT I 1

BATTERY I I EFI MAIN RELA

4A-FE ENGINE FOR EUROPE

F

W

+1

3

C

FUEL PUMP CONTRO

CIRCUIT OPENING RELA

CHECK ENGINE LAMP

(Diagnostic code display

Y

.

(

Apr

., 1992)

L

Y

)

.

.

OUTLINE OF TCCS

- System Descriptio

n

®

COMPONENTS AND FUNCTION

S

The sensors, Engine ECU, and actuators, which
are the basis of the engine control system, are
shown in the following table, along with their

relationship with the main functions of the

engine control system, EFI, ESA and ISC

COMPONENTS

Manifold pressure senso

vacuum sensor)(D-type

(

EFI

)

Air flow meter

(L-type EFI)

Distributor

Sensors

Actuators

Water temp

Intake air temp

Throttle position

(

on-off type)

Throttle position sensor

(

linear type)

Ignition switch
Vehicle speed sensor

Oxygen sensor

sensor)

(02

Variable resistor

Neutral start switch

Taillight & defogger relays

Air conditioner
Knock sensor

Engine ECU

Injectors

Igniter

Idle speed control valve

. sensor

. sensor

sensor

.

SIG-

NAL

r

PIM

VS, KS

orVG

G

NE

THW

THA

IDL

PSW

IDL

VTA

STA
SPD

OX

VAF

NSW

ELS

A/C

KNK

No

.10

No

.20

IGT

IGF

ISC

REFERENCE

The signals used for each control may differ for
some engines

S

Senses intake manifold pressure

Senses intake air volume

Senses crankshaft angle

Senses engine speed
Senses coolant
Senses intake air temperature
Senses when throttle valve is fully closed
Senses when throttle valve near fully open
Senses when throttle valve is fully closed

Senses throttle valve opening angle

Senses when ignition switch is start position
Senses vehicle speed

Senses oxygen density in exhaust gas

It is used to change the air-fuel ratio of the idl

mixture

Senses whether transmission is in "P" or "N"
or in some other gear

Senses electrical load

Senses whether air conditioner is on or off
Senses engine knocking

Determines injection duration and timing, igni

tion timing, idle speed, etc

from sensors and data stored in memory, an

sends appropriate signals to control actuators

Injects fuel into intake manifold in accordanc
with signals from Engine ECU

When IGT signals from Engine ECU go off

primary

sparks are generated by spark plugs

then sends IGF signals to Engine ECU

Controls idle speed by changing volume of ai
flowing through throttle valve bypass in accor
dance with signals from Engine ECU

.

current to igniter is interrupted, an

FUNCTIONS

temperature

.

.

.

.

.

.

.
.

.

., based upon dat

EFI

ESAISC

.

.

.

.

.

.

.

.

e

,

.

­a
d

.

e

.

,

d

. Ignite

.

.

r

r

-

11

a

3

. ENGINE CONTROL SYSTEM DIAGRA

OUTLINE OF

TCCS - System Descriptio

M

n

Check connecto

Neutral start

switch

~

~

r

Fuel pump

Fuel tank

Speed
senso

J

Combination

r

mete

Circuit opening
rela

y

Air
conditioner
amplifier

r

Taillight relay

Defogger relay

~

r-o

r

i

f

Engine EC

U

Ignition

~ ENGINE

~ lam

switc

CHECK

p

"

Batter

h

y

Distributor and
ignite

r

Pressure regulator /

Injector

*Applicable only to General Country specification vehicles without oxygen sensor

Knock

sensor

Water temp

. sensor

Variable

resistor

Oxygen sensor

(02 sensor)

/

TW

C

.

*

12

COROLLA 4A-FE

ENGINE FOR

EUROPE (Apr

., 1992)

ELECTRONIC CONTROL SYSTEM - Genera

l

41

1

ELECTRONIC CONTROL SYSTE

GENERA

The engine control system can be divided into
three groups
them), the ECU, and actuators
describes only the sensor (signal) systems
ECU functions are divided into EFI control, ESA
control, ISC control, diagnostic function, fail-safe
function, back-up function and others

these functions is covered in a separate section

of this manual

Actuator functions are also covered in a

separate section

Power circuitry

VC circuitry
Ground circuitry

Manifold pressure
(vacuum sensor)

Air flow meter

Throttle

position sensor

G and

NE signa

enerators

g

Water temperature sensor

Intake air temperature

Oxygen sensor

sensor)

(02

Lean mixture sensor

` Specifications

L

: sensors (and the signals output by

. This section

. Each of

.

.

SENSORS (SIGNALS)

Engine
motor

Engine with steppe
motor type ISC valve

senso

Vane type

type

l

for Carolla AE101 4A-FE engine (Apr

without steppe

type ISC valve

r

r

Optcal Karman vorte

Hot-wire type

On-off type

Linear

type

In-distributor

Cam position sensor type
Separate type

sensor

Zirconia element type

Titania element type

type

r

x

.

PAG

E

(THI

S

MANUAL)

15

1

6

16
16

17

1

8

2

21-

22

23

24
27
28

30

30
31

3 2

3 3

The following table shows the specifications for
the 4A-FE engine
their signals) marked with a circle in the

"APPENDIX" column is included in the
specifications for each engine in the APPENDIX
section (page 188) at the back of this manual
Sensors (signals) covered in Step 2, vol
are covered in outline form only in this manual
If there is a circle in the "STEP 2(EFI)" column in
the following table, refer to the Step 2, vol
(EFI), for a detailed explanation of the relevant
sensors (and their signals)

ITEM

0

0
0

0

1

1

0

., 1992)

With TW

M

. Information on sensors (and

.

REMARK

C

APPENDIX

(Continued

.

5 (EFI),

STEP

(EFI

)

on next page

.

.

. 5

2

)

13

Vehicle speed

sensor

SENSORS (SIGNALS)

Reed switch type

Photocoupler type

Electromagnetic pickup

typ

e

ELECTRONIC CONTROL SYSTEM - Genera

PAG

E

(THIS

MANUAL)

3

4

3

4

3 5

ITEM*

REMARK

l

STEP

APPENDIX

(EFI

2

)

MRE (magnetic resistance
element) typ

e

STA (ignition switch) signal
NSW (neutral start switch 1 signal

A/C (air conditioner) signal

Electrical load signal
Fuel control switch or connector

EGR gas temperature sensor

Variable resistor

Kick-down switch

Water temperature switch

Clutch switch

Knock sensor

HAC (high-altitude compensation) sensor

Turbocharging pressure sensor

Stop lamp switch
Oil pressure switch

Throttle opening angle
signal

s

Throttle opening angl

e

signals for TRC (traction
control) syste

m

Cruise control system

communications signa

TRC system

Communications
signals

communications signa
ABS (anti-lock brak

e
system) communications
signa

l

Intercooler system

warning signa

l

EHPS lelectro-hydrauli
power steering) system
communications signa

Engine speed signal

Diagnostic terminal (s)

• Specifications for Corolla AE101 4A-FE engine (Apr

36

38

~

J

~
38
39
39

0
0

40

40

41

r~

C

Californi
specification model

Except with oxyge

senso

a

s

n

r

42
42

42

43

With knockin
correction for ES

g

A

44

44

45
4

5

4

5

4

5

4

l

l

6

4

6

4

6

4

6

c

4

7

l

4

7

4

7

., 1992

)

14

ELECTRONIC CONTROL SYSTEM

- Power Circuitr

y

®

POWER CIRCUITR

Y

This circuitry supplies power to the Engine ECU,
and includes the ignition switch and the EFI main

relay

. There are two types of this circuitry in

use

. In one, current flows directly from the

ignition switch to the EFI main relay coil to
operate the EFI main relay (the type without the
stepper motor type ISC valve)

. In the other, the
Engine ECU operates the EFI main relay directly
(the type with the stepper motor type ISC Battery

valve)

.

1

. ENGINE WITHOUT STEPPER MOTOR

TYPE ISC VALV

E

The following diagrams show the type in which
the EFI main relay is operated directly from the

ignition switch

. When the ignition switch is
turned on, current flows to the coil of the EFI
main relay, causing the contacts to close
supplies power to the +B and +B1 terminals of
the Engine ECU

. Battery voltage is supplied at
all times to the BATT terminal of the Engine ECU
to prevent the diagnostic codes and other data

in its memory from being erased when the
ignition switch is turned off

.
There are two types of circuitry for the type
without a stepper motor, depending on the
vehicle model

.

. This

ELECTRICAL CIRCUITR

EFI fus

e

To stop lamp switc

STOP fus

Battery

* Some models only

e

Y

Engine EC

BATT

h

Engine EC

OHP

OHP 7

U

7

U

15

ELECTRONIC CONTROL SYSTEM

2

. ENGINE WITH STEPPER MOTOR TYPE

ISC VALV

E

The diagram below shows the type in which the
EFI main relay is operated from the Engine ECU
In engines with the stepper motor type ISC
valve, since initial set control is carried out
when the ignition switch is turned off, power is

supplied to the Engine ECU for this purpose for
approximately 2 seconds after the ignition
switch is turned off
page 105

.) When the ignition switch is turned on,

. (For further details, see

battery voltage is supplied to the IGSW terminal
of the Engine ECU, and the EFI main relay
control circuitry in the Engine ECU sends a signal
to the M-REL terminal of the Engine ECU,
turning on the EFI main relay

. This signal causes

current to flow to the coil, closing the contacts
of the EFI main relay and supplying power to the
+B and +B1 terminals of the Engine ECU

. Battery

voltage is supplied at all times to the BATT
terminal of the Engine ECU to prevent the
diagnostic codes and other data in its memory
from being erased when the ignition switch is

turned off

ELECTRICAL CIRCUITR

Battery

.

EFI fus

Y

Engine ECU

e

- Power Circuitry, VC Circuitry, Ground Circuitr

ELECTRICAL CIRCUITR

Engine EC

Y

U

.

Some

models only

1 Outputs 5 V from the 5-V constant-voltage

circuit

.

2 Outputs 5 V from the 5-V constant-voltag

circuit through a resistor

~ NOT

E

.

When the VC circuit is open or shorted, each of
the sensors using the 5 V constant voltage of

the VC is no longer activated
In addition, since the microprocessor will no

longer be activated when the VC circuit is
shorted, the engine ECU will not operate
result, the engine will stall

GROUND

CIRCUITR

.

The Engine ECU has the following three types of
basic ground circuitry

•

El

terminal, which grounds the Engine ECU

:

• E2 terminal, which grounds the sensors

• E01 and E02 terminals, which ground the drive
circuits for the injectors or ISC valve, etc

These ground circuits are connected inside the
Engine ECU as shown in the following diagram

.

Y

y

OHP

8

e

. As a

.

.

.

.

Some models only

OHP 7

VC CIRCUITR

Y

The Engine ECU generates a constant 5 volts to

power the microprocessor from the battery

voltages supplied to the +B and +B1 terminals
The Engine ECU supplies this 5 V of power to the

sensors through

16

circuitry

like that shown below

ELECTRICAL CIRCUITR

To sensors

.

To ground E01

E2

.

E

l

E0

2

Y

Engine ECU

/I

-

.

OHP

8

ELECTRONIC CONTROL SYSTEM

MANIFOLD PRESSURE SENSOR
(VACUUM SENSOR

)

- Manifold Pressure Sensor (Vacuum Sensor

)

The manifold pressure sensor is used with D­type EFI for sensing the intake manifold

pressure

.

This is one of the most important sensors in D­type EFI

.
By means of an IC built into this sensor, the
manifold pressure sensor senses the intake
manifold pressure as a PIM signal

. The Engine

ECU then determines the basic injection duration
and basic ignition advance angle on the basis of

this PIM signal

.

A change in the intake manifold pressure causes
the shape of the silicon chip to change, and the

resistance value of the chip fluctuates in
accordance with the degree of deformation

This fluctuation in the resistance value is

converted to a voltage signal by the IC built into
the sensor and is then sent to the Engine ECU

from the PIM terminal as an intake manifold
pressure signal

. The VC terminal of the Engine
ECU supplies a constant 5 volts as a power
source for the IC

(V)

4

~

3

rn

.

.

Intake manifold pressure

OHP 9

f

Intake manifold pressur

OPERATION AND FUNCTION
A silicon chip combined with a vacuum chamber

maintained at a predetermined vacuum is
incorporated into the sensor unit

the chip is exposed to intake manifold pressure
and the other side is exposed to the internal
vacuum chamber

.

e

OHP

. One side of

0 20 60 100 kPa (abs)

(760, 29

9

.9) (610, 24

.0) (310,

Intake manifold pressure

ELECTRICAL CIRCUITR

Manifold pressure

sensor

IC

12.2)

Y

VC

PI

M

E2

E

(10, 0

Engine EC

1

l

.4) (mmHg

in

.Hg

[vacuum]

OHP

U

5

V

R

,

)

9

/

To intake manifol

Silicon chip

d

OHP 10

17

®

ELECTRONIC CONTROL SYSTEM

- Manifold Pressure Sensor (Vacuum Sensor),
Air Flow Mete

r

NOTE

The manifold pressure sensor uses the
vacuum in the vacuum chamber that is built

into it

. The vacuum in this chamber is close to

a perfect vacuum, and is not influenced by the

changes in atmospheric pressure that occur

due to changes in altitude

.

The manifold pressure sensor compares the

intake manifold pressure to this vacuum, and
outputs a PIM signal which is not influenced

by changes in atmospheric pressure

.

This permits the ECU to keep the air-fuel ratio

at the optimal level even at high altitudes

Perfect

vacuum pressur

p 101

(0, 0) (760, 29

101

.3

(760, 29.9)

Vacuum

Atmospheri

Absolute pressur

0

(0, 0

c

e

.3 200 kPa

.9) (1500, 59

)

(sea level

.1) (mmHg,

. ... . .

. .

.

e

)

.

in.Hg)

AIR FLOW METE

R

The air flow meter is used with L-type EFI for
sensing the intake air volume

.

In L-type EFI, this is one of the most important

sensors

calculate the basic injection duration

ignition advance angle
The following three types of air flow
used

1

. The intake air volume signal is used t

:

Volume air flow

meter

Mass air flow _ Hot-wire type
mete

r

. VANE TYP

-

F

L

E

.

Vane type

Optical

and basi

meter ar

Karman vortex typ

There are two types of vane type air flow meter
These differ in the nature of their electrical
circuitry, but the components for the two types
are the same

.

This type of air flow meter is composed of many
components, as shown in the following

illustration

:

o
c

e

e

.

Vacuum

0

(0, 0

)

(high altitude)

OHP 10

Slide

r

Return spring

Potentiomete

Bypass passag

Measuring plate

r

Idle mixture
adjusting screw

e

OHP 1

1

18

ELECTRONIC CONTROL SYSTEM

- Air Flow Mete

r

®

OPERATION AND FUNCTIO

N

When air passes through the air flow meter from
the air cleaner, it pushes open the measuring

plate until the force acting on the measuring

plate is in equilibrium with the return spring
The potentiometer, which is connected coaxially
with the measuring plate, converts the intake air
volume to a voltage signal (VS signal) which is

sent to the Engine ECU

. The damping chamber

and compensation plate act to prevent the

measuring plate from vibrating when the air

intake volume changes suddenly

Potentiometer

.

REFERENCE

Standard Adjustment Mark of Idle Mixture
Adjusting Scre

w

As shown in the illustration, a two digit
number is stamped on the air flow meter near

.

the idle mixture adjusting screw

. This number
indicates the distance from the body upper
surface to the flat surface of the screw when
the VS voltage of the air flow meter is at the
standard voltage at the time that the volume
of air through the bypass was adjusted during
final inspection of the air flow meter at the
factory

means that the distance was 13
in)

distance was 12

. For example, if the number is "30", it

.0 mm (0

. If the number is "26", it indicates the

.6 mm (0

Air flow meter

.496 in)

Idle mixture

adjusting scre

.

.511

w

IDLE MIXTURE ADJUSTING SCRE

W

An idle mixture adjusting screw is included in
the bypass passage

. This screw is used to adjust

the volume of intake air which bypasses the

measuring plate, and can be used to adjust the
idle mixture. (Some engines are equipped with

air flow meters which are sealed with an
aluminum plug

.)

OHP 1

1

Idle mixture

adjusting screw

19

®

VS SIGNAL

ELECTRONIC CONTROL SYSTEM

- Air Flow Mete

r

There are two types of vane type air flow meter,
which differ in the nature of their electrical

circuitry

. In one type, the VS voltage falls when

the air intake volume becomes large and in the

other type, the VS voltage rises when the air
intake volume becomes large

1 Type

1

.

The Engine ECU has a built-in constant-voltage

circuit, which supplies a constant 5 V to the VC

terminal of the air flow meter

. Consequently,

the output voltage at the VS terminal will

always indicate the exact opening angle of the
measuring plate, and therefore, the exact intake
air volume

.

Fuel pump switch

Potentiomete

f2)

Type

2

This type of

battery voltage from the VB terminal

air flow meter is supplied with

.
This type of air flow meter does not have a
constant voltage (5 V) supplied from the Engine
ECU, so the voltage determined by the ratio of
the resistances of the resistor between VB and
VC and the resistor between VC and E2 is input
to the Engine ECU via the VC terminal

.
As a result, even when the VS voltage is
affected by fluctuations in the ba

ttery

voltage,
the Engine ECU, by executing the following
calculation, can detect the intake air volume

accurately

Intake air volume

:

=

VB

- E2

VB - E2

(VC - E2) - (VS - E2) VC - VS

For further details, see Step 2, vol

r

Fuel pump switch Potentiomete

.

5 (EFI)

r

.

20

Voltage (V)

FC E1 E2 VC E2

(E1) (FC)

~a~n~a~ff

5

.0-

i

0

1

Measuring plate opening angl

(intake air volume)

v

;o-ts

a

VC H E

VS H E

VS

THA

OHP 1

OHP 12

Voltage of batte

A

2

2

e

OHP 1

2

Voltage (V)

0
Measuring plate opening angl

r

y

VBHE

VC"E

VS H E

(intake air volume) OHP 12

2

2

2

e

2

ELECTRONIC CONTROL SYSTEM

- Air Flow Mete

r

®

2

. OPTICAL KARMAN VORTEX TYP

E

This type of air flow meter directly senses the

intake air volume optically

. Compared to the

vane type air flow meter, it can be made smaller
and lighter in weight

. The simplified construction

of the air passage also reduces inlet resistance
This air flow meter is constructed as shown in

the following illustration

Mirror

From

moo,

air

creaner ~9

W~'M

Vortex

generator OHP 1

/

OPERATION AND FUNCTIO
A pillar (called the "vo

:

LED

Pressure­directin

___.. 9 Phntntrancictn

Leaf sprin

Karman

n

v

N

rt

ex generator") placed in

g

I To air

.toYO~ chambe

the middle of a uniform flow of air generates a

vortex called
of the pillar

a "Karmanvort

.

ex" down-stream

The frequency "f" of the Karman vortex thus
generated, the velocity of the air "V" and the
diameter of the pillar "d" have the following

relationship

:

♦

r

.

intake

of a piece of thin metal foil (called a "mirror") to
the pressure of the vortexes and optically

detecting the vibrations of the mirror by means
of a photocoupler (an LED combined with a

D

Vortex -

generato

.

Phototransisto

r

Mirro

~ Pressur

~ directing

r

r

e

apertur

OHP 1

e

3

phototransistor)

LE

r=^

r

The intake air volume (KS) signal is a pulse

3

signal like that shown below

. When the intake
air volume is low, this signal has a low
frequency
this signal has a high frequency

Voltage

signa

. When the intake air volume is high,

High

l

Low

Low

Intake air volume

.

Hig

h

OHP 1

3

f - K x d

Pillar (vortex generator

KARMAN VORTEX

)

Utilizing this principle, the frequency of the

vortexes generated by the vortex generator is

measured, making it possible to determine the
air flow volume

exes are detected by subjecting the su

Vo

rt

.

OHP 1

rf

ace

ELECTRICAL CIRCUITR

Air flow mete

3

Phototransistor

r

Y

Engine EC

OHP 1

U

3

21

4

3

. HOT-WIRE TYPE

ELECTRONIC CONTROL

SYSTEM - Air Flow Mete

r

Instead of measuring intake air volume in the man­ner of other air flow meters, a hot-wire type air
flow meter measures intake air mass directly
The structure is both compact and lightweight
addition, there is only a low level of intake

resistance by the sensor

Having no mechanical functions it offers a

superior durability

.

.

.

. In

OPERATION AND FUNCTI

Current flows to the hot-wire (heater) causing it
to be heated
the hot-wire is cooled corresponding to the intake

air mass
hot-wire in order to keep the hot-wire temperature

constant, that current becomes proportional to in­take air mass
measured by detecting that current
hot-wire type air flow meters, this current is con­verted into a voltage that is then output to the
Engine ECU

. When air flows through the wire,

. By controlling the current flowing to the

. Intake air mass can then be

.

N

O

. In case of

Thermisto

~ REFERENC

A hot-wire type air flow meter as shown below

F

E

is used on some models

r

.

Thermistor

Hot-wire (heater)

*Constant temperatur

*

Intake air mass --

e

(g/sec

-

.)

ELECTRONIC

CONTROL SYSTEM

- Air Flow Mete

r

®

In an actual air flow meter, a hot-wire is incor­porated into the bridge circuit . This bridge circuit
has the characteristic of the potentials at points A
and B being equal when the product of resistance
along the diagonal line is equal ([Ra + R3] • R1 =
Rh • R2)

. When the hot-wire (Rh) is cooled by in­take air, resistance decreases resulting in the for­mation of a difference between the potentials of

points A and B

. An operational amplifier detects
this difference and causes a rise in the voltage ap­plied to the circuit (increases the current flowing
to the hot-wire (Rh))

. When this is done, the

temperature of the hot-wire (Rh) again rises

resulting in a corresponding increase in resistance
until the potentials of points A and B become
equal (the voltages of points A and B become
higher)

. By utilizing the properties of this type of
bridge circuit, the air flow meter is able to
measure intake air mass by detecting the voltage
at point B

. Moreover, in this system, the

temperature of the hot-wire (Rh) is continuously
maintained at a constant temperature higher than

the temperature of the intake air by using the ther­mistor (Ra)

.

Consequently, since intake air mass can be
measured accurately even if intake air
temperature changes, it is not necessary for the
Engine ECU to correct the fuel injection duration

for the intake air temperature

. In addition, when

air density decreases at high altitudes, the cooling

capacity of the air decreases in comparison with

the same intake air volume at sea level

. As a

result, the amount of cooling of the hot-wire is
reduced

. Since the intake air mass detected will
also decrease the high-altitude compensation cor­rection is not necessary

.

Diagram Indicating Principle of Electrical

Air flow meter

REFERENCE
The voltage (V) required to raise the
temperature of the hot-wire (Rh) by the amount
of

AT

from the intake air temperature remains
constant at all times even if the intake air
temperature changes

capacity of the air is always proportional to the
intake air mass

mass remains the same, the output of the air
flow meter will not change even if there is a
change in intake air temperature

20°C+AT --

0°C+OT --

20°C

0°C

. In addition, the coolin

. Consequently, if the intake air

.

Hot-wire (Rh) temperatur

Intake air temperatur

v

NOTE

An intake air temperature sensor is not required
for the measurement of intake air mass due to
the properties of a hot-wire type air flow meter
However, since intake air temperature is re­quired for other electronic control systems of
the engine, the hot-wire type air flow meter has
the built-in intake air temperature sensor

Circuitr

Engine

EC

.

y

U

g

e

e

.

ELECTRONIC CONTROL SYSTEM

- Throttle Position Senso

r

THROTTLE

The throttle position sensor is mounted on the

throttle body
opening angle to a voltage and sends it to the

Engine ECU as the thro
The IDL signal is used mainly in fuel cut-off
control and ignition timing corrections and the

VTA or

the fuel injection volume to increase engine

output

PSW signal is used mainly for increasing

.

POSITION SENSO

. This sensor converts the throttle

tt

le opening angle signal

There are two types of throttle position sensor,

as follows

:

• On-off type

• Linear typ

1

. ON-OFF TYP

This type of throttle position sensor detects
whether the engine is idling or running under a

heavy load by means of the idle (IDL) contact or
power (PSW) contact

Other terminals or contacts can also be used to
perform other functions, depending on the type

of engine. These include
(LSW) contact, for lean burn correction

L2, and L3 terminals for control of the ECT
ACC1 and ACC2 terminals for sensing

acceleration; etc
vol

. 5 (EFI)

e

E

.

: the lean burn switch

; the L1,

. For further details, see Step 2,

.

R

; the

2 3-contact typ

.

3 With L1, L2 and L3

4 With ACC1 and ACC2

IDL

ACC

e

terminal

2

s

terminal

s

1 2-contact type

PSW ~

E

IDL

IDL H E

PSW H E ' Off

22

On

~

i

Throttle valve

Of

f

I

---)

O

n

Open

OHP 14

ELECTRICAL CIRCUITRY (2-CONTACT TYPE

OHP 1

)

4