Subaru Legacy IV (2008 year). Manual - part 133

EN(H4SO)(diag)-135

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Y: DTC P0125 INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP 

FUEL CONTROL

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-40, DTC P0125 INSUFFICIENT COOLANT TEMPERA-
TURE FOR CLOSED LOOP FUEL CONTROL, Diagnostic Trouble Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
Engine does not return to idle.

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.

Step

Check

Yes

No

1

CHECK TIRE SIZE.

Is the tire size as specified and 
the same size as three other 
wheels?

Go to step 2.

Replace the tire.

2

CHECK ENGINE COOLANT.
Check the following items:
• Amount of engine coolant
• Engine coolant freeze
• Contamination of engine coolant

Is the engine coolant normal?

Go to step 3.

Fill or replace the 
engine coolant. 
<Ref. to 
CO(H4SO)-13, 
REPLACEMENT, 
Engine Coolant.>

3

CHECK THERMOSTAT.

Does the thermostat remain 
opened?

Replace the ther-
mostat. <Ref. to 
CO(H4SO)-17, 
Thermostat.>

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H4SO)-22,
Engine Coolant 
Temperature Sen-
sor.>

EN(H4SO)(diag)-136

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Z: DTC P0126 INSUFFICIENT ENGINE COOLANT TEMPERATURE FOR STABLE 

OPERATION

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-42, DTC P0126 INSUFFICIENT ENGINE COOLANT
TEMPERATURE FOR STABLE OPERATION, Diagnostic Trouble Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
• Hard to start
• Improper idling
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

EN-04033

29

34

19

8

B134

ECM

1

2

E2

B21

E8

E8

B21

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

B134

ENGINE

COOLANT

TEMPERATURE

SENSOR

1 2

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

EN(H4SO)(diag)-137

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK ENGINE COOLANT TEMPERATURE 
SENSOR.
Measure the resistance between engine cool-
ant temperature sensor terminals when the 
engine coolant is cold and after warmed up.

Terminals

No. 1 — No. 2:

Is the resistance of engine cool-
ant temperature sensor differ-
ent between when engine 
coolant is cold and after 
warmed up?

Repair the poor 
contact of ECM 
connector.

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H4SO)-22,
Engine Coolant 
Temperature Sen-
sor.>

EN(H4SO)(diag)-138

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

AA:DTC P0128 COOLANT THERMOSTAT (ENGINE COOLANT TEMPERATURE 

BELOW THERMOSTAT REGULATING TEMPERATURE)

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-44, DTC P0128 COOLANT THERMOSTAT (ENGINE
COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE), Diagnostic Trouble
Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
Thermostat remains open.

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.

Step

Check

Yes

No

1

CHECK ENGINE COOLANT.

Are the coolant level and mix-
ture ratio of engine coolant to 
anti-freeze solution correct?

Go to step 2.

Replace the 
engine coolant. 
<Ref. to 
CO(H4SO)-13, 
REPLACEMENT, 
Engine Coolant.>

2

CHECK RADIATOR FAN.
1) Start the engine.
2) Check the radiator fan operation.

Does the radiator fan continu-
ously rotate for 3 minutes or 
more during idling?

Repair radiator fan 
circuit. <Ref. to 
CO(H4SO)-24, 
Radiator Main Fan 
and Fan Motor.> 
and <Ref. to 
CO(H4SO)-26, 
Radiator Sub Fan 
and Fan Motor.>

Replace the ther-
mostat. <Ref. to 
CO(H4SO)-17, 
Thermostat.>