Lexus GS300/400 (2000 year). Service manual — part 160

Z17007

Fig. 4

Sensor

2

1

A

C

1

1

2

2

B

5V

5V

5V

0V

Z17008

Fig. 5

2

1

A

C

1

1

2

2

B

SHORT

Z17009

Fig. 6

2

1

A

C

1

1

2

2

B

Sensor

ECU

IN–34

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

34

(b)

Check the voltage.
In a circuit in which voltage is applied (to the ECU connec-
tor terminal), an open circuit can be checked for by con-
ducting a voltage check.

As shown in Fig. 4, with each connector still con-
nected, measure the voltage between body ground
and terminal 1 of connector ”A” at the ECU 5V out-
put terminal, terminal 1 of connector ”B”, and termi-
nal 1 of connector ”C”, in that order.

If the results are:
5V: Between Terminal 1 of connector ”A” and Body Ground
5V: Between Terminal 1 of connector ”B” and Body Ground
0V: Between Terminal 1 of connector ”C” and Body Ground
Then it is found out that there is an open circuit in the wire har-
ness between terminal 1 of ”B” and terminal 1 of ”C”.

7.

CHECK SHORT CIRCUIT

If the wire harness is ground shorted as in Fig. 5, locate the sec-
tion by conducting a ”continuity check with ground”.

Check the continuity with ground.

(1)

Disconnect connectors ”A” and ”C” and measure
the resistance between terminal 1 and 2 of connec-
tor ”A” and body ground.
In the case of Fig. 6
Between terminal 1 of connector ”A” and body
ground

→

Continuity (short)

Between terminal 2 of connector ”A” and body
ground

→

No continuity

Therefore, it is found out that there is a short circuit
between terminal 1 of connector ”A” and terminal 1
of connector ”C”.

Z17808

Fig. 7

Sensor

2

1

A

B1

C

1

1

2

2

1

2

B2

ECU

IN0383

Example

Ground

IN0384

Ground

Ground

ECU Side

W/H Side

–

INTRODUCTION

HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS

IN–35

35

(2)

Disconnect connector ”B” and measure the resis-
tance between terminal 1 of connector ”A” and body
ground, and terminal 1 of connector ”B2” and body
ground.
Between terminal 1 of connector ”A” and body
ground

→

No continuity

Between terminal 1 of connector ”B2” and body
ground

→

Continuity (short)

Therefore, it is found out that there is a short circuit
between terminal 1 of connector ”B2” and terminal
1 of connector ”C”.

8.

CHECK AND REPLACE ECU

First check the ECU ground circuit. If it is faulty, repair it. If it is
normal, the ECU could be faulty, so replace the ECU with a nor-
mal functioning one and check that the symptoms appear.

(1)

Measure the resistance between the ECU ground
terminal and the body ground.

Resistance: 1

Ω

or less

(2)

Disconnect the ECU connector, check the ground
terminals on the ECU side and the wire harness
side for bend and check the contact pressure.

IN04Q–07

IN–36

–

INTRODUCTION

TERMS

36

TERMS

ABBREVIATIONS USED IN THIS MANUAL

Abbreviations

Meaning

ABS

Anti–Lock Brake System

AC

Alternating Current

ACC

Accessory

ACIS

Acoustic Control Induction System

ACSD

Automatic Cold Start Device

A.D.D.

Automatic Disconnecting Differential

A/F

Air–Fuel Ratio

AHC

Active Height Control Suspension

ALR

Automatic Locking Retractor

ALT

Alternator

AMP

Amplifier

ANT

Antenna

APPROX.

Approximately

A/T

Automatic Transmission (Transaxle)

ATF

Automatic Transmission Fluid

AUTO

Automatic

AUX

Auxiliary

AVG

Average

AVS

Adaptive Variable Suspension

BA

Brake Assist

BACS

Boost Altitude Compensation System

BAT

Battery

BDC

Bottom Dead Center

B/L

Bi–Level

B/S

Bore–Stroke Ratio

BTDC

Before Top Dead Center

BVSV

Bimetallic Vacuum Switching Valve

Calif.

California

CB

Circuit Breaker

CCo

Catalytic Converter For Oxidation

CD

Compact Disc

CF

Cornering Force

CG

Center Of Gravity

CH

Channel

COMB.

Combination

CPE

Coupe

CPS

Combustion Pressure Sensor

CPU

Central Processing Unit

CRS

Child Restraint System

CTR

Center

C/V

Check Valve

CV

Control Valve

–

INTRODUCTION

TERMS

IN–37

37

CW

Curb Weight

DC

Direct Current

DEF

Defogger

DFL

Deflector

DIFF.

Differential

DIFF. LOCK

Differential Lock

D/INJ

Direct Injection

DLI

Distributorless Ignition

DOHC

Double Over Head Cam

DP

Dash Pot

DS

Dead Soak

DSP

Digital Signal Processor

EBD

Electronic Brake Force Distribution

ECAM

Engine Control And Measurement System

ECD

Electronic Controlled Diesel

ECDY

Eddy Current Dynamometer

ECU

Electronic Control Unit

ED

Electro–Deposited Coating

EDIC

Electric Diesel Injection Control

EDU

Electronic Driving Unit

EFI

Electronic Fuel Injection

E/G

Engine

EGR–VM

Egr–Vacuum Modulator

ELR

Emergency Locking Retractor

ENG

Engine

ESA

Electronic Spark Advance

ETCS

Electronic Throttle Control System

EVP

Evaporator

E–VRV

Electric Vacuum Regulating Valve

EXH

Exhaust

FE

Fuel Economy

FF

Front–Engine Front–Wheel–Drive

F/G

Fuel Gage

FIPG

Formed In Place Gasket

FL

Fusible Link

F/P

Fuel Pump

FPU

Fuel Pressure Up

Fr

Front

FR

Front–Engine Rear–Wheel–Drive

F/W

Flywheel

FW/D

Flywheel Damper

FWD

Front–Wheel–Drive

GAS

Gasoline

GND

Ground

HAC

High Altitude Compensator

H/B

Hatchback