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.