Subaru Legacy (2005 year). Manual - part 331

EN(H4DOTC)(diag)-93

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(H4DOTC)(diag)-24, Subaru Select Mon-
itor.>
• 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(H4DOTC)(diag)-94

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(H4DOTC)-22, 
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

EN(H4DOTC)(diag)-95

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

M: DTC P0122 THROTTLE/PEDAL POSITION SENSOR/SWITCH “A” CIRCUIT 

LOW

DTC DETECTING CONDITION:
Immediately at fault recognition
TROUBLE SYMPTOM:
• Erroneous idling
• Engine stalls.
• Poor driving performance
WIRING DIAGRAM:

EN-03524

SBF-7

B135

B:

B137

B136

D:

B362

B84

B138

B122

E1

B20

E57

C:

B135

B362

B20

B21

E57

B84

B122

B138

B137

B136

E

E

D6

B35

16

15

*

*

*

*

7
3

E2

B21

39

38

19

20

35

36

37

4

6

1

2

3

5

D4

D5

C35

C16

B1

B4

D1

D2

D3

C29

C18

5

8

7

6

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

1 2

7 8

3
4

5
6

1 2 3 4 5 6 7 8 9 10 11

12 13 14 15 16 17 18 19 20 21 22
23 24 25

34 35

36 37 38 39 40 41

48 49

50 51 52 53 54

42 43

44 45

46 47

26 27 28 29 30 31 32 33

1 2 3 4
5 6 7 8

1 2 3 4 5 6

1

2

7

8 9

5

6

3

4

10 11 12

19 20 21

29

30 31

13 14 15 16 17

27

28

18

22 23

24 25

26

1

2

7

8 9

5

6

3

4

10 11 12

19

20 21

29 30 31

13 14 15 16 17

27

28

18

22 23

24 25

26

32 33

34 35

1

2

8 9

5

6

3

4

10 11 12

19 20 21

29 30

31

13 14 15 16

17

27

28

18

22 23 24 25 26

7

32 33 34 35

B:

D:

C:

ECM

BATTERY

MAIN RELAY

ELECTRONIC
THROTTLE 
CONTROL RELAY

ELECTRONIC
THROTTLE 
CONTROL

*

: TERMINAL No. RANDOM ARRANGEMENT

EN(H4DOTC)(diag)-96

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK SENSOR OUTPUT.
1) Turn the ignition switch to ON.
2) Read the data of main throttle 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(H4DOTC)(diag)-24, Subaru Select Mon-
itor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the voltage more than 0.4 V? Go to step 2.

Go to step 3.

2

CHECK POOR CONTACT.
Check poor contact in connector between 
ECM and electronic throttle control.

Is there poor contact in con-
nector between ECM and elec-
tronic throttle control?

Repair the poor 
contact.

Temporary poor 
contact occurred, 
but it is normal at 
present.

3

CHECK HARNESS BETWEEN ECM AND 
ELECTRONIC THROTTLE CONTROL.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Disconnect the connectors from electronic 
throttle control.
4) Measure the resistance between ECM con-
nector and electronic throttle control connector.

Connector & terminal

(B136) No. 16 — (E57) No. 5:
(B136) No. 18 — (E57) No. 6:

Is the resistance less than 1 
Ω?

Go to step 4.

Repair the open 
circuit of harness 
connector.

4

CHECK HARNESS BETWEEN ECM AND 
ELECTRONIC THROTTLE CONTROL.
Measure the resistance between ECM connec-
tor and chassis ground.

Connector & terminal

(B136) No. 18 — Chassis ground:
(B136) No. 16 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 5.

Repair the chas-
sis short circuit of 
harness.

5

CHECK POWER SUPPLY OF ELECTRONIC 
THROTTLE CONTROL.
1) Connect the ECM connector.
2) Turn the ignition switch to ON.
3) Measure the voltage between electronic 
throttle control connector and engine ground.

Connector & terminal

(E57) No. 5 (+) — Engine ground (

−

):

Is the voltage 4.5 — 5.5 V?

Go to step 6.

Repair the poor 
contact in ECM 
connector. 
Replace the ECM 
if defective. <Ref. 
to FU(H4DOTC)-
34, Engine Con-
trol Module 
(ECM).>

6

CHECK SHORT CIRCUIT INSIDE THE ECM.
1) Turn the ignition switch to OFF.
2) Measure the resistance between electronic 
throttle control connector and engine ground.

Connector & terminal

(E57) No. 6 — Engine ground:

Is the resistance more than 10 
Ω?

Repair the poor 
contact of elec-
tronic throttle con-
trol connector. 
Replace the elec-
tronic throttle con-
trol if defective.

Repair the poor 
contact in ECM 
connector. 
Replace the ECM 
if defective. <Ref. 
to FU(H4DOTC)-
34, Engine Con-
trol Module 
(ECM).>