Subaru Legacy (2005 year). Manual - part 450

EN(H6DO)(diag)-113

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK CURRENT DATA.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor or gen-
eral scan tool to data link connector.
3) Turn the ignition switch to ON, and turn the 
power switch of Subaru Select Monitor or gen-
eral scan tool to ON.
4) Start the engine.
5) Read the voltage of mass air flow sensor 
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)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the voltage 0.2 — 4.7 V?

Even if the mal-
function indicator 
light illuminates, 
the circuit has 
returned to a nor-
mal condition at 
this time. A tempo-
rary poor contact 
in connector or 
harness may be 
the cause. Repair 
harness or con-
nector in the mass 
air flow sensor.

NOTE:
In this case, repair
the following:
• Open or ground 
short circuit of har-
ness between 
mass air flow sen-
sor and ECM con-
nector
• Poor contact in 
mass air flow sen-
sor or ECM con-
nector

Go to step 2.

2

CHECK INPUT SIGNAL OF ECM.
Measure the voltage between ECM connector 
and chassis ground while engine is idling.

Connector & terminal

(B136) No. 23 (+) — Chassis ground (

−

):

Is the voltage more than 0.2 V? Go to step 4.

Go to step 3.

3

CHECK INPUT SIGNAL OF ECM (USING 
SUBARU SELECT MONITOR).
Measure the voltage between ECM connector 
and chassis ground while engine is idling.

Does the voltage change by 
shaking the harness and con-
nector of ECM while monitor-
ing the value with Subaru 
Select Monitor?

Repair the poor 
contact in ECM 
connector.

Replace the ECM. 
<Ref. to 
FU(H6DO)-34, 
Engine Control 
Module (ECM).>

4

CHECK POWER SUPPLY TO MASS AIR 
FLOW SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from mass air 
flow sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between mass air flow 
sensor connector and chassis ground.

Connector & terminal

(B3) No. 1 (+) — Chassis ground (

−

):

Is the voltage more than 5 V?

Go to step 5.

Repair the open 
circuit between 
mass air flow sen-
sor and main relay.

5

CHECK HARNESS BETWEEN ECM AND 
MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness 
between ECM and mass air flow sensor con-
nector.

Connector & terminal

(B136) No. 23 — (B3) No. 3:
(B136) No. 31 — (B3) No. 2:
(B136) No. 35 — (B3) No. 5:

Is the resistance less than 1 
Ω?

Go to step 6.

Repair the open 
circuit between 
ECM and mass air 
flow sensor con-
nector.

EN(H6DO)(diag)-114

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

6

CHECK HARNESS BETWEEN ECM AND 
MASS AIR FLOW SENSOR CONNECTOR
Measure the resistance of harness between 
ECM and chassis ground.

Connector & terminal

(B136) No. 23 — Chassis ground:
(B136) No. 31 — Chassis ground:
(B136) No. 35 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 7.

Repair the ground 
short circuit 
between ECM and 
mass air flow sen-
sor connector.

7

CHECK POOR CONTACT.
Check poor contact in mass air flow sensor 
connector.

Is there poor contact in mass 
air flow sensor connector?

Repair the poor 
contact in mass air 
flow sensor con-
nector.

Replace the mass 
air flow and intake 
air temperature 
sensor. <Ref. to 
FU(H6DO)-24, 
Mass Air Flow and 
Intake Air Temper-
ature Sensor.>

Step

Check

Yes

No

EN(H6DO)(diag)-115

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

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

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

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)(diag)-41, 
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)(diag)-34, PROCEDURE, 
Inspection Mode.>.
WIRING DIAGRAM:

EN-03496

B83

B3

BATTERY

E

B83

1

B3

MASS AIR FLOW AND INTAKE 
AIR TEMPERATURE SENSOR

ECM

B136

SBF-7

1 2 3 4 5

3

4

1

2

5

6

B136

B47

*

*

2

4

3

5

31

13

23

35

32

MAIN  RELAY

B47

1 2 3 4
5 6 7 8

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

6
4

 : TERMINAL No.
   RANDOM ARRANGEMENT

*

EN(H6DO)(diag)-116

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK CURRENT DATA.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor or gen-
eral scan tool to data link connector.
3) Turn the ignition switch to ON, and turn the 
power switch of Subaru Select Monitor or gen-
eral scan tool to ON.
4) Start the engine.
5) Read the voltage of mass air flow sensor 
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)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the voltage 0.2 — 4.7 V?

Even if the mal-
function indicator 
light illuminates, 
the circuit has 
returned to a nor-
mal condition at 
this time.

Go to step 2.

2

CHECK HARNESS BETWEEN ECM AND 
MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from mass air-
flow sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between mass air flow 
sensor connector and chassis ground.

Connector & terminal

(B3) No. 3 (+) — Chassis ground (

−

):

Is the voltage more than 5 V?

Repair the battery 
short circuit of har-
ness between 
mass air flow sen-
sor connector and 
ECM connector.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND 
MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness 
between ECM connector and mass air flow 
sensor connector.

Connector & terminal

(B3) No. 2 — (B136) No. 31:

Is the resistance less than 1 
Ω?

Replace the mass 
air flow sensor. 
<Ref. to 
FU(H6DO)-24, 
Mass Air Flow and 
Intake Air Temper-
ature Sensor.>

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