Subaru Legacy (2005 year). Manual - part 454

EN(H6DO)(diag)-129

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of engine coolant tempera-
ture sensor signal using Subaru Select Monitor 
or general scan tool.

NOTE:

• Subaru Select Monitor
For detailed operation procedure, refer to 
“READ CURRENT DATA FOR ENGINE”. <Ref. 
to EN(H6DO)(diag)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the engine coolant tempera-
ture more than 150

°C (302°F)?

Go to step 2.

Repair the poor 
contact.

NOTE:
In this case, repair
the following:
• Poor contact in 
engine coolant 
temperature sen-
sor
• Poor contact in 
ECM
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

2

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from engine cool-
ant temperature sensor.
3) Turn the ignition switch to ON.
4) Read the data of engine coolant tempera-
ture sensor signal using Subaru Select Monitor 
or general scan tool.

NOTE:

• Subaru Select Monitor
For detailed operation procedure, refer to 
“READ CURRENT DATA FOR ENGINE”. <Ref. 
to EN(H6DO)(diag)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the engine coolant tempera-
ture less than 

−40°C (−40°F)?

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H6DO)-18, 
Engine Coolant 
Temperature Sen-
sor.>

Repair the ground 
short circuit of har-
ness between 
engine coolant 
temperature sen-
sor and ECM con-
nector.

EN(H6DO)(diag)-130

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AA:DTC P0118 ENGINE COOLANT TEMPERATURE CIRCUIT HIGH

DTC DETECTING CONDITION:
Immediately at fault recognition
TROUBLE SYMPTOM:
• Hard to start
• Erroneous idling
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)(diag)-41, 
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)(diag)-34, PROCEDURE, 
Inspection Mode.>.
WIRING DIAGRAM:

EN-03498

*

*

B83

35

14

19

8

B136

ECM

1

2

E2

B21

E8

ENGINE

COOLANT

TEMPERATURE

SENSOR

E8

B21

1 2 3 4
5 6 7 8

B83

1 2 3 4

12 13 14 15

5 6 7 8

16 17 18 19

9 10 11

20 21 22

23 24 25 26 27 28 29 30 31 32 33

35

34

37

36

39

38

41

40

43

42

44

45

47

46

49

48

51

50

53

52

54

B136

5

6

7 8

2

1

9

4

3

10

24

22 23

25

11 12 13 14 15

26 27

28

16

17 18 19 20 21

33 34

29

32

30

31

35

*

 : TERMINAL No. RANDOM ARRANGEMENT

1 2

EN(H6DO)(diag)-131

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of engine coolant tempera-
ture sensor signal using Subaru Select Monitor 
or general scan tool.

NOTE:

• Subaru Select Monitor
For detailed operation procedure, refer to 
“READ CURRENT DATA FOR ENGINE”. <Ref. 
to EN(H6DO)(diag)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the engine coolant tempera-
ture less than 

−40°C (−40°F)?

Go to step 2.

Repair the poor 
contact.

NOTE:
In this case, repair
the following:
• Poor contact in 
engine coolant 
temperature sen-
sor
• Poor contact in 
ECM
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

2

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from engine cool-
ant temperature sensor.
3) Measure the voltage between engine cool-
ant temperature sensor connector and engine 
ground.

Connector & terminal

(E8) No. 2 (+) — Engine ground (

−

):

Is the voltage more than 10 V? Repair the battery 

short circuit of har-
ness between 
ECM and engine 
coolant tempera-
ture sensor con-
nector.

Go to step 3.

3

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
1) Turn the ignition switch to ON.
2) Measure the voltage between engine cool-
ant temperature sensor connector and engine 
ground.

Connector & terminal

(E8) No. 2 (+) — Engine ground (

−

):

Is the voltage more than 10 V? Repair the battery 

short circuit of har-
ness between 
ECM and engine 
coolant tempera-
ture sensor con-
nector.

Go to step 4.

4

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
Measure the voltage between engine coolant 
temperature sensor connector and engine 
ground.

Connector & terminal

(E8) No. 2 (+) — Engine ground (

−

):

Is the voltage more than 4 V?

Go to step 5.

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:
• Open circuit of 
harness between 
ECM and engine 
coolant tempera-
ture sensor con-
nector
• Poor contact in 
engine coolant 
temperature sen-
sor connector
• Poor contact in 
ECM connector
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

EN(H6DO)(diag)-132

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

5

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance of harness 
between engine coolant temperature sensor 
connector and engine ground.

Connector & terminal

(E8) No. 1 — Engine ground:

Is the resistance less than 5 
Ω?

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H6DO)-18, 
Engine Coolant 
Temperature Sen-
sor.>

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:
• Open circuit of 
harness between 
ECM and engine 
coolant tempera-
ture sensor con-
nector
• Poor contact in 
engine coolant 
temperature sen-
sor connector
• Poor contact in 
ECM connector
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

Step

Check

Yes

No