
INTRODUCTION - HOW TO TROUBLESHOOT ECU CONTROLLED 01-37
SYSTEMS
01046-08
ELECTRONIC CIRCUIT INSPECTION PROCEDURE
1. BASIC INSPECTION
(a) RESISTANCE MEASURING CONDITION OF ELECTRONIC PARTS
(1) Unless stated, all resistance is measured at an ambient temperature of 20_C (68_F). As the re-
sistance may be outside the specifications if measured at high temperatures immediately after
the vehicle has been running, measurements should be made when the engine has cooled
down.
(b)
HANDLING OF CONNECTOR
(1) When removing the connector with lock, press the
connector in the direction of the engagement and
remove the lock by lightly pressing the lock claw.
(2) When removing the connector, do not hold the har-
ness, but hold the connector.
(3) Before connecting the connector, check that there
is no deformation, damage or missing terminals.
(4) The connector with a lock should be securely con-
nected until it makes a "click" sound.
(5) When checking the connector with a Toyota electri-
WRONG cal tester, check it from the backside (harness side)
of the connector using a mini test lead.
NOTICE:
S As a water proof connector cannot be checked from
the backside, check by connecting the sub-harness.
S Do not damage the terminals by moving the inserted
tester needle.
CORRECT
D25086 (c) CONNECTOR CHECKING POINTS
(1) Checking when the connector is connected:
By holding the connector, check the inserted condi-
tion and locking efficiency (engaged condition).
Looseness of Crimping (2) Checking when the connector is removed:
Check by lightly pulling the wire harness (missing
terminal, terminal crimping condition, core wire
break).
Core Wire
Check visually for is any rust, metal particles, water
Terminal and bent terminals (rust, mixing of foreign object,
Deformation terminal deformation).
Pull Lightly NOTICE:
D25087 When testing a gold-plated female terminal, always use a
gold-plated male terminal.
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01-38 INTRODUCTION - HOW TO TROUBLESHOOT ECU CONTROLLED
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(3) Checking of the contact pressure of the terminal:
Prepare a spare male terminal.
Insert it into a female terminal, check the engaged
condition and sliding resistance.
Same terminal as
a male terminal D25088
(d) REPAIR METHOD OF CONNECTOR TERMINAL
(1) If there is on the contact point, clean the contact
point using an air gun or shop rag. However, never
polish the contact point using sand paper as the
platings may come off.
(2) In case of abnormal contact pressure, replace the
female terminal. However, if a male terminal is gold-
WRONG
plated (gold color), use gold-plated female terminal
CORRECT
D20024 and if it is silver-plated (silver color), use silver-
plated female terminal.
(e) HANDLING OF WIRE HARNESS
WRONG (1) When removing the wire harness, check the posi-
tioning of the wiring and clamping before starting
work in order to be able to restore it correctly.
(2) Never twist, pull or loosen the wire harness more
than necessary.
(3) Never allow the wire harness to come into contact
with a high-temperature, rotating, moving, vibrating
D01557 or sharp (edge of the panel, tip of the screw, etc.)
part.
(4) When installing parts, never let the wire harness be
interfered with.
(5) Never cut or break the cover of the wire harness. If
one is cut or broken, replace it or securely repair it
with electrical tape.
Fig. 1
2. CHECK OPEN CIRCUIT
ECU (a) For the open circuit in the wire harness in Fig. 1, perform
C OPEN B A a continuity check in step (b) or a voltage check in step (c)
Sensor 1 1 1 1 to locate the section.
2 2 2 2
Z17004
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INTRODUCTION - HOW TO TROUBLESHOOT ECU CONTROLLED 01-39
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Fig. 2 (b) Check the continuity.
(1) Disconnect connectors A and C and measure the
resistance between them.
ECU Resistance: 1 or less
Sensor 1 1 HINT:
1
2 2 2 Measure the resistance while lightly shaking the wire harness
C B A vertically and horizontally.
In the case of Fig. 2:
Z17005 Between terminal 1 of connector A and terminal 1
of connector C No continuity (open)
Between terminal 2 of connector A and terminal 2
of connector C Continuity
Therefore, the cause is an open circuit between ter-
minal 1 of connector A and terminal 1 of connector
C.
Fig. 3 (2) Disconnect connector B and measure the resis-
tance between the connectors.
ECU In the case of Fig. 3:
Between terminal 1 of connector A and terminal 1
Sensor
of connector B1 Continuity
Between terminal 1 of connector B2 and terminal 1
1 1 1 1 of connector C No continuity (open)
2 2 2 2 Therefore, the cause is an open circuit between ter-
C B2 B1 A
B04722 minal 1 of connector B2 and terminal 1 of connector
C.
Fig. 4 (c) Check the voltage.
(1) In a circuit in which voltage is applied (to the ECU
connector terminal), an open circuit can be checked
5V by conducting a voltage check.
Sensor 0V 5V
As shown in Fig. 4, with each connector still con-
1 1 1
nected, measure the voltage between the body
2 2 2
ground and terminal 1 of connector A at the ECU 5
B A
C V output terminal, terminal 1 of connector B, and
Z17007 terminal 1 of connector C, in that order.
(2) If the results are:
5 V: Between terminal 1 of connector A and body
ground
5 V: Between terminal 1 of connector B and body
ground
0 V: Between terminal 1 of connector C and body
ground
Therefore, the cause is an open circuit in the wire
harness between terminal 1 of connector B and ter-
minal 1 of connector C.
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01-40 INTRODUCTION - HOW TO TROUBLESHOOT ECU CONTROLLED
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Fig. 5 3. CHECK SHORT CIRCUIT
(a) If the wire harness is ground shorted as shown in Fig. 5,
C SHORT B A locate the section by conducting a continuity check with
1 1 1 the body ground in step (b).
2 2 2
Z17008
Fig. 6 (b) Check the continuity with the body ground.
(1) Disconnect connectors A and C and measure the
resistance between terminals 1 and 2 of connector
ECU A and the body ground.
Sensor Resistance: 10 k or higher
1 1 1 HINT:
2 2 2
C
Measure the resistance while lightly shaking the wire harness
B A
vertically and horizontally.
Z17009 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, the cause is a short circuit between ter-
minal 1 of connector A and terminal 1 of connector
C.
Fig. 7 (2) Disconnect connector B and measure the resis-
tance between terminal 1 of connector A and the
body ground, and terminal 1 of connector B2 and
the body ground.
ECU
In the case of Fig. 7:
Sensor
1 1 1 1 Between terminal 1 of connector A and body
2 2 2 2 ground No continuity
C B2 B1 A
Between terminal 1 of connector B2 and body
Z17808 ground Continuity (short)
Therefore, the cause is a short circuit between ter-
minal 1 of connector B2 and terminal 1 of connector
C.
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4. CHECK AND REPLACE ECU
NOTICE:
S Start an inspection of the connector from the back-
side of the connector on the wire harness side with
the connector connected to the ECU.
S When no measurement condition is specified, per-
form the inspection with the engine stopped and also
the ignition switch ON.
(a) First check the ECU ground circuit. If it is faulty, repair it.
If it is normal, the ECU could be faulty. In this case, re-
place the ECU with one that functions normally and check
if the symptoms appear.
Example (1) Measure the resistance between the ECU ground
terminal and body ground.
Resistance: 1 or less
Ground
IN0383
ECU Side (2) Disconnect the ECU connector, check the ground
terminals on the ECU side and wire harness side for
bends and check the contact pressure.
Ground
W/H Side
Ground
IN0384
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