Lexus ES300 (1997 year). Manual — part 491
IN0379
Sensor Side
ECU Side
IN0378
Sensor Side
ECU Side
IN0380
Sensor Side
ECU Side
IN0381
Pull Lightly
Looseness of Crimping
IN–28
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INTRODUCTION
HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS
28
1997 LEXUS ES300 (RM511U)
2.
CONTINUITY CHECK (OPEN CIRCUIT CHECK)
(a)
Disconnect the connectors at both ECU and sensor
sides.
(b)
Measure the resistance between the applicable terminals
of the connectors.
Resistance: 1
Ω
or less
HINT:
Measure the resistance while lightly shaking the wire har-
ness vertically and horizontally.
When tester probes are inserted into a connector, insert
the probes from the back. For waterproof connectors in
which the probes cannot be inserted from the back, be
careful not to bend the terminals when inserting the tester
probes.
3.
RESISTANCE CHECK (SHORT CIRCUIT CHECK)
(a)
Disconnect the connectors on both ends.
(b)
Measure the resistance between the applicable terminals
of the connectors and body ground. Be sure to carry out
this check on the connectors on both ends.
Resistance: 1 M
Ω
or higher
HINT:
Measure the resistance while lightly shaking the wire harness
vertically and horizontally.
4.
VISUAL CHECK AND CONTACT PRESSURE CHECK
(a)
Disconnect the connectors at both ends.
(b)
Check for rust or foreign material, etc. in the terminals of
the connectors.
(c)
Check crimped portions for looseness or damage and
check that the terminals are secured in lock portion.
HINT:
The terminals should not come out when pulled lightly.
(d)
Prepare a test male terminal and insert it in the female ter-
minal, then pull it out.
NOTICE:
When testing a gold–plated female terminal, always use a
gold–plated male terminal.
HINT:
When the test terminal is pulled out more easily than others,
there may be poor contact in that section.
FI7187
Z17004
C
B
A
OPEN
Sensor
Fig. 1
ECU
1
2
1
2
1
2
2
1
Z17005
Fig. 2
Sensor
ECU
C
B
A
1
2
1
2
1
2
B04722
Fig. 3
ECU
Sensor
2
1
A
B1
C
1
1
2
2
1
2
B2
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INTRODUCTION
HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS
IN–29
29
1997 LEXUS ES300 (RM511U)
5.
CONNECTOR HANDLING
When inserting tester probes into a connector, insert them from
the rear of the connector. When necessary, use mini test leads.
For water resistant connectors which cannot be accessed from
behind, take good care not to deform the connector terminals.
6.
CHECK OPEN CIRCUIT
For the open circuit in the wire harness in Fig. 1, perform ”(a)
Continuity Check” or ”(b) Voltage Check” to locate the section.
(a)
Check the continuity.
(1)
Disconnect connectors ”A” and ”C” and measure
the resistance between them.
In the case of Fig. 2,
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, it is found out that there is an open circuit
between terminal 1 of connector ”A” and terminal 1
of connector ”C”.
(2)
Disconnect connector ”B” and measure the resis-
tance between the connectors.
In the case of Fig. 3,
Between terminal 1 of connector ”A” and terminal 1
of connector ”B1”
→
Continuity
Between terminal 1 of connector ”B2” and terminal
1 of connector ”C”
→
No continuity (open)
Therefore, it is found out that there is an open circuit
between terminal 1 of connector ”B2” and terminal
1 of connector ”C”.
Z17007
Fig. 4
Sensor C
A
1
2
1
2
1
2
ECU
B
5 V
5 V
0 V
5 V
Z17008
C
B
A
SHORT
Fig. 5
1
2
1
2
2
1
Z17009
Fig. 6
Sensor
ECU
C
B
A
1
2
1
2
1
2
IN–30
–
INTRODUCTION
HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS
30
1997 LEXUS ES300 (RM511U)
(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 connected,
measure the voltage between body ground and terminal
1 of connector ”A” at the ECU 5V output terminal, terminal
1 of connector ”B”, and terminal 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
ECU
C
A
1
2
1
2
1
2
2
1
B2
B1
IN0383
Example
Ground
IN0384
ECU Side
Ground
W/H Side
Ground
–
INTRODUCTION
HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS
IN–31
31
1997 LEXUS ES300 (RM511U)
(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.
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