Subaru Legacy III (2000-2003 year). Manual - part 128

EN(H4SO)-124

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

M: DTC P0118 — ENGINE COOLANT TEMPERATURE CIRCUIT HIGH INPUT —

• 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(H4SO)-47, OPER-
ATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)-40, OPERATION, Inspection 
Mode.> .
• WIRING DIAGRAM:

EN-01125

19

12

9

13

B135 ECM

2

1

E2

B21

E8

ENGINE

COOLANT

TEMPERATURE 

SENSOR

E8

B21

1 2

3 4

5

6 7

8

9 10

11 12

13

14 15

16

17 18

19 20

1 2

3

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

B135

B83

1 2 3 4 5 6

B83

3

1

FG

2

4

EG

: FOR G.C.C COUNTRIES MODEL 

: EXCEPT FOR G.C.C COUNTRIES MODEL 

FG

EG

EN(H4SO)-125

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK CURRENT DATA.
1) Start engine.
2) Read data of engine coolant temperature 

sensor signal using Subaru Select Monitor 
or OBD-II general scan tool.
Is the measured value less than the speci-
fied value?

NOTE:

•Subaru Select Monitor
For detailed operation procedure, refer to the 
“READ CURRENT DATA FOR ENGINE”. 
<Ref. to EN(H4SO)-32, Subaru Select Moni-
tor.>  
•OBD-II general scan tool
For detailed operation procedures, refer to the 
OBD-II General Scan Tool Instruction Manual.

−

40

°

C (

−

40

°

F)

Go to step 2.

Repair poor con-
tact.

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 ignition switch to OFF.
2) Disconnect connector from engine coolant 

temperature sensor.

3) Measure voltage between engine coolant 

temperature sensor connector and engine 
ground.

Connector & terminal

(E8) No. 1 (+) — Engine ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

Repair battery 
short circuit in 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 ignition switch to ON.
2) Measure voltage between engine coolant 

temperature sensor connector and engine 
ground.

Connector & terminal

(E8) No. 1 (+) — Engine ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

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

Go to step 4.

EN(H4SO)-126

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

4

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

Connector & terminal

(E8) No. 1 (+) — Engine ground (

−−−−

):

Does the measured value exceed the specified 
value?

4 V

Go to step 5.

Repair harness 
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in 
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

5

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
1) Turn ignition switch to OFF.
2) Measure resistance of harness between 

engine coolant temperature sensor connec-
tor and engine ground.

Connector & terminal

(E8) No. 2 — Engine ground:

Is the measured value less than the speci-
fied value?

5 

Ω

Replace engine 
coolant tempera-
ture sensor. <Ref. 
to FU(H4SO)-26, 
Engine Coolant 
Temperature Sen-
sor.>

Repair harness 
and connector.

NOTE:
In this case, repair
the following:

• Open circuit in 
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

Value

Yes

No

EN(H4SO)-127

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO: