Subaru Legacy (2005 year). Manual - part 124

EN(H4SO 2.0)(diag)-85

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector 
and chassis ground.

Connector & terminal

(B136) No. 17 (+) — Chassis ground (

−

):

Is the voltage more than 4.5 V? Go to step 3.

Go to step 2.

2

CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector 
and chassis ground.

Connector & terminal

(B136) No. 17 (+) — Chassis ground (

−

):

Does the voltage change by 
shaking the ECM harness and 
connector?

Repair the poor 
contact in ECM 
connector.

Replace the ECM. 
<Ref. to FU(H4SO 
2.0)-34, Engine 
Control Module 
(ECM).>

3

CHECK INPUT SIGNAL OF ECM.
Measure the voltage between ECM connector 
and chassis ground.

Connector & terminal

(B136) No. 20 (+) — Chassis ground (

−

):

Is the voltage more than 4.5V? Go to step 5.

Go to step 4.

4

CHECK INPUT SIGNAL OF ECM (USING 
SUBARU SELECT MONITOR).
Read the data of atmospheric absolute pres-
sure signal using Subaru Select Monitor.

NOTE:

For detailed operation procedure, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4SO 2.0)(diag)-25, Subaru Select Mon-
itor.>

Is the value more than 13.3 
kPa (100 mmHg, 3.94 inHg) 
when shaking the ECM har-
ness and connector?

Repair the poor 
contact in ECM 
connector.

Go to step 5.

5

CHECK HARNESS BETWEEN ECM AND 
MANIFOLD ABSOLUTE PRESSURE SEN-
SOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from manifold 
absolute pressure sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between manifold 
absolute pressure sensor connector and 
engine ground.

Connector & terminal

(E21) No. 3 (+) — Engine ground (

−

):

Is the voltage more than 4.5 V? Go to step 6.

Repair the open 
circuit of harness 
between ECM and 
manifold absolute 
pressure sensor 
connector.

6

CHECK HARNESS BETWEEN ECM AND 
MANIFOLD ABSOLUTE PRESSURE SEN-
SOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness 
between ECM and manifold absolute pressure 
sensor connector.

Connector & terminal

(B136) No. 20 — (E21) No. 2:

Is the resistance less than 1 
Ω?

Go to step 7.

Repair the open 
circuit of harness 
between ECM and 
manifold absolute 
pressure sensor 
connector.

7

CHECK HARNESS BETWEEN ECM AND 
MANIFOLD ABSOLUTE PRESSURE SEN-
SOR CONNECTOR.
1)Turn the ignition switch to ON.
2)Measure the voltage between ECM connec-
tor and chassis ground.

Connector & terminal

(B136) No. 20 (+) — Chassis ground (

−

):

Is the voltage more than 4.5 V? Repair the short 

circuit of harness 
between ECM and 
manifold pressure 
sensor connector.

Go to step 8.

EN(H4SO 2.0)(diag)-86

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

8

CHECK HARNESS BETWEEN ECM AND 
MANIFOLD ABSOLUTE PRESSURE SEN-
SOR CONNECTOR.
1)Turn the ignition switch to OFF.
2)Measure the resistance of harness between 
ECM and manifold absolute pressure sensor 
connector.

Connector & terminal

(B136) No. 18 — (E21) No. 1:

Is the resistance less than 1 
Ω?

Go to step 9.

Repair the open 
circuit of harness 
between ECM and 
manifold absolute 
pressure sensor 
connector.

9

CHECK POOR CONTACT.
Check poor contact in manifold absolute pres-
sure sensor connector.

Is there poor contact in mani-
fold absolute pressure sensor 
connector?

Repair the poor 
contact in mani-
fold absolute pres-
sure sensor 
connector.

Replace the mani-
fold absolute pres-
sure sensor. <Ref. 
to FU(H4SO 2.0)-
26, Manifold Abso-
lute Pressure Sen-
sor.>

Step

Check

Yes

No

EN(H4SO 2.0)(diag)-87

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

H: DTC P0112 INTAKE AIR TEMPERATURE SENSOR 1 CIRCUIT LOW

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

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO 2.0)(diag)-
38, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.0)(diag)-32, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-03478

28

18

INTAKE AIR

TEMPERATURE

SENSOR

19

6

B21

E2

2

1

E20

E20

ECM

B21

B136

1 2 3 4
5 6 7 8

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

1 2

B138

B83

B83

:LHD

B138 :RHD

*

*

*

: TERMINAL No. RANDOM ARRANGEMENT
  AMONG 1,2,5, AND 6

EN(H4SO 2.0)(diag)-88

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 intake air temperature 
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(H4SO 2.0)(diag)-25, Subaru Select 
Monitor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the intake air temperature 
more than 120

°C (248°F)?

Go to step 2.

Repair the poor 
contact.

NOTE:
In this case, repair
the following item:
• Poor contact in 
intake air tempera-
ture sensor
• Poor contact in 
ECM
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

2

CHECK HARNESS BETWEEN INTAKE AIR 
TEMPERATURE SENSOR AND ECM CON-
NECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from intake air 
temperature sensor.
3) Turn the ignition switch to ON.
4) Read the data of intake air temperature 
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(H4SO 2.0)(diag)-25, Subaru Select 
Monitor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the intake air temperature 
less than 

−40°C (−40°F)?

Replace the intake 
air temperature 
sensor. <Ref. to 
FU(H4SO 2.0)-27, 
Intake Air Temper-
ature Sensor.>

Repair the ground 
short circuit of har-
ness between 
intake air tempera-
ture sensor and 
ECM connector.