Subaru Legacy IV (2008 year). Service manual — part 539

EN(H6DO)(diag)-129

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

W: DTC P0102 MASS OR VOLUME AIR FLOW CIRCUIT LOW INPUT

DTC DETECTING CONDITION:
• Immediately at fault recognition
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-33, DTC P0102 MASS OR VOLUME AIR FLOW CIRCUIT
LOW INPUT, Diagnostic Trouble Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
• Improper idling
• Engine stalls.
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H6DO)(diag)-52,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H6DO)(diag)-44, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

EN-03920

B83

B3

BATTERY

E

B83

1

B3

MASS AIR FLOW & INTAKE
AIR TEMPERATURE SENSOR

ECM

B135

SBF-7

1 2 3 4 5

3

4

1

2

5

6

B135

B47

*

*

2

4

3

5

34

18

26

30

35

MAIN RELAY

B47

1

2

4

6

3

5

1 2 3 4
5 6 7 8

*

: TERMINAL No.
OPTIONAL ARRANGEMENT

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

29 30 31

32 33

34 35

EN(H6DO)(diag)-130

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of air flow 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(H6DO)(diag)-34, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the voltage less than 0.2 V?

Go to step 2.

Even if DTC is
detected, the cir-
cuit has returned to
a normal condition
at this time. Repro-
duce the failure,
and then perform
the diagnosis
again.

NOTE:
In this case, tem-
porary poor con-
tact of connector
may be the cause.

2

CHECK POWER SUPPLY OF MASS AIR
FLOW AND INTAKE AIR TEMPERATURE
SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from the mass air
flow and intake air temperature sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between mass air flow
and intake air temperature sensor connector
and engine ground.

Connector & terminal

(B3) No. 1 (+) — Engine ground (–):

Is the voltage 10 V or more?

Go to step 3.

Repair the harness
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
main relay and
mass air flow and
intake air tempera-
ture sensor con-
nector
• Poor contact of
main relay connec-
tor

3

CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW AND INTAKE AIR TEM-
PERATURE SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM.
3) Measure the resistance of harness between
ECM and mass air flow and intake air tempera-
ture sensor connectors.

Connector & terminal

(B135) No. 26 — (B3) No. 3:

Is the resistance less than 1

:? Go to step 4.

Repair the open
circuit of harness
between ECM and
mass air flow and
intake air tempera-
ture sensor con-
nector.

4

CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW AND INTAKE AIR TEM-
PERATURE SENSOR CONNECTOR.
Measure the resistance between ECM and
chassis ground.

Connector & terminal

(B135) No. 26 — Chassis ground:

Is the resistance 1 M

: or

more?

Go to step 5.

Repair the ground
short circuit of har-
ness between the
ECM and the mass
air flow and intake
air temperature
sensor connectors.

5

CHECK POOR CONTACT.
Check for any poor contact in the ECM or the
mass air flow or intake air temperature sensor
connector.

Is there poor contact in the
ECM or the mass air flow and
intake air temperature sensor
connector?

Repair any poor
contact in the ECM
or the mass air flow
and intake air tem-
perature sensor
connector.

Replace the mass
air flow and intake
air temperature
sensor. <Ref. to
FU(H6DO)-26,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>

EN(H6DO)(diag)-131

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

X: DTC P0103 MASS OR VOLUME AIR FLOW CIRCUIT HIGH INPUT

DTC DETECTING CONDITION:
• Immediately at fault recognition
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-34, DTC P0103 MASS OR VOLUME AIR FLOW CIRCUIT
HIGH INPUT, Diagnostic Trouble Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
• Improper idling
• Engine stalls.
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H6DO)(diag)-52,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H6DO)(diag)-44, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

EN-03920

B83

B3

BATTERY

E

B83

1

B3

MASS AIR FLOW & INTAKE
AIR TEMPERATURE SENSOR

ECM

B135

SBF-7

1 2 3 4 5

3

4

1

2

5

6

B135

B47

*

*

2

4

3

5

34

18

26

30

35

MAIN RELAY

B47

1

2

4

6

3

5

1 2 3 4
5 6 7 8

*

: TERMINAL No.
OPTIONAL ARRANGEMENT

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

29 30 31

32 33

34 35

EN(H6DO)(diag)-132

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of air flow 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(H6DO)(diag)-34, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the voltage 5 V or more?

Go to step 2.

Even if DTC is
detected, the cir-
cuit has returned to
a normal condition
at this time. Repro-
duce the failure,
and then perform
the diagnosis
again.

NOTE:
In this case, tem-
porary poor con-
tact of connector
may be the cause.

2

CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW AND INTAKE AIR TEM-
PERATURE SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from the mass air
flow and intake air temperature sensor.
3) Start the engine.
4) Read the data of air flow 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(H6DO)(diag)-34, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the voltage 5 V or more?

Repair the short
circuit to power in
the harness
between the ECM
and the mass air
flow and intake air
temperature sen-
sor connector.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW AND INTAKE AIR TEM-
PERATURE SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance of harness between
mass air flow and intake air temperature sensor
connector and engine ground.

Connector & terminal

(B3) No. 2 — Engine ground:

Is the resistance less than 5

:? Go to step 4.

Repair the harness
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and mass air
flow and intake air
temperature sen-
sor connectors.
• Poor contact in
ECM connector

4

CHECK POOR CONTACT.
Check for any poor contact in the mass air flow
and intake air temperature sensor connector.

Is there poor contact in the
mass air flow and intake air
temperature sensor connector?

Repair any poor
contact of the
mass air flow and
intake air tempera-
ture sensor con-
nector.

Replace the mass
air flow and intake
air temperature
sensor. <Ref. to
FU(H6DO)-26,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>