Subaru Legacy IV (2008 year). Manual - part 554

EN(H6DO)(diag)-189

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

BD:DTC P0175 SYSTEM TOO RICH (BANK 2)

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-74, DTC P0175 SYSTEM TOO RICH (BANK 2), Diagnos-
tic 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.>.

Step

Check

Yes

No

1

CHECK EXHAUST SYSTEM.

Are there holes or loose bolts 
on exhaust system?

Repair the exhaust 
system.

Go to step 2.

2

CHECK AIR INTAKE SYSTEM.

Are there holes, loose bolts or 
disconnection of hose on air 
intake system?

Repair the air 
intake system.

Go to step 3.

3

CHECK FUEL PRESSURE.

WARNING:
Place “NO OPEN FLAMES” signs near the
working area.

CAUTION:
Be careful not to spill fuel.
Measure the fuel pressure. <Ref. to 
ME(H6DO)-27, INSPECTION, Fuel Pressure.>

CAUTION:
Release fuel pressure before removing the
fuel pressure gauge.

Is the measured value 333 — 
343 kPa (3.4 — 3.5 kgf/cm

2

,

48.4 — 49.8 psi)?

Go to step 4.

Repair the follow-
ing item.
Fuel pressure is 
too high:
• Clogged fuel line 
or bent hose
Fuel pressure is 
too low:
• Improper fuel 
pump discharge
• Clogged fuel line

4

CHECK ENGINE COOLANT TEMPERATURE 
SENSOR.
1) Start the engine and warm up completely.
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(H6DO)(diag)-34, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the engine coolant tempera-
ture 75°C (167°F) or higher?

Go to step 5.

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H6DO)-20, 
Engine Coolant 
Temperature Sen-
sor.>

EN(H6DO)(diag)-190

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

5

CHECK MASS AIR FLOW AND INTAKE AIR 
TEMPERATURE SENSOR SIGNAL.
1) Start the engine and warm up engine until 
coolant temperature is higher than 75°C 
(167°F).
2) Place the select lever in “P” range or “N” 
range.
3) Turn the A/C switch to OFF.
4) Turn all the accessory switches to OFF.
5) Read the data of the mass air flow and 
intake air temperature sensor signal using Sub-
aru 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 measured value 2.0 — 
5.0 g/s (0.26 — 0.66 lb/m)?

Go to step 6.

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

6

CHECK MASS AIR FLOW AND INTAKE AIR 
TEMPERATURE SENSOR.
1) Start the engine and warm up engine until 
coolant temperature is higher than 75°C 
(167°F).
2) Place the select lever in “P” range or “N” 
range.
3) Turn the A/C switch to OFF.
4) Turn all the accessory switches to OFF.
5) Open the front hood.
6) Measure the ambient temperature.
7) Read the data of the mass air flow and 
intake air temperature sensor signal using Sub-
aru 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.

Subtract ambient temperature 
from intake air temperature. Is 
the obtained value –10 — 50°C 
(–18 — 90°F)?

Repair the poor 
contact of ECM 
connector.

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

Step

Check

Yes

No

EN(H6DO)(diag)-191

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

BE:DTC P0181 FUEL TEMPERATURE SENSOR “A” CIRCUIT RANGE/

PERFORMANCE

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-75, DTC P0181 FUEL TEMPERATURE SENSOR “A”
CIRCUIT RANGE/PERFORMANCE, Diagnostic Trouble Code (DTC) Detecting Criteria.>

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:

B83

30

17

B135

R58

R67

R46

R1

B97

B97

R67

R58

B135

2

3

1

4

4

18

B83

1

2

3 4 5 6

1 2
3 4
5 6

1 2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

3 4

5 6

1 2

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

29 30 31

32 33

34 35

EN-05659

FUEL PUMP ASSY

FUEL TEMPERATURE 
SENSOR

ECM

: TERMINAL No. OPTIONAL 
  ARRANGEMENT

EN(H6DO)(diag)-192

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK FOR ANY OTHER DTC ON DISPLAY. Is any other DTC displayed?

Check the appro-
priate DTC using 
the “List of Diag-
nostic Trouble 
Code (DTC)”. 
<Ref. to 
EN(H6DO)(diag)-
81, List of Diagnos-
tic Trouble Code 
(DTC).>

Replace the fuel 
temperature sen-
sor. <Ref. to 
EC(H6DO)-10,
Fuel Temperature 
Sensor.>