Subaru Legacy (2005 year). Manual - part 463

EN(H6DO)(diag)-165

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AQ:DTC P0171 SYSTEM TOO LEAN (BANK 1)

Refer to DTC P0175 for diagnostic procedure. <Ref. to EN(H6DO)(diag)-166, DTC P0175 SYSTEM TOO
RICH (BANK 2), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

AR:DTC P0172 SYSTEM TOO RICH (BANK 1)

Refer to DTC P0175 for diagnostic procedure. <Ref. to EN(H6DO)(diag)-166, DTC P0175 SYSTEM TOO
RICH (BANK 2), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

AS:DTC P0174 SYSTEM TOO LEAN (BANK 2)

Refer to DTC P0175 for diagnostic procedure. <Ref. to EN(H6DO)(diag)-166, DTC P0175 SYSTEM TOO
RICH (BANK 2), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

5

CHECK EXHAUST SYSTEM.
Check exhaust system parts.

NOTE:

Check the following items.
• Loose part and incomplete installation of 
exhaust system
• Damage (crack, hole etc.) of parts
• Looseness and ill fitting of parts between 
front oxygen (A/F) sensor and rear oxygen 
sensor

Is there any fault in exhaust 
system?

Repair or replace 
faulty parts.

Replace the rear 
oxygen sensor. 
<Ref. to 
FU(H6DO)-32, 
Rear Oxygen Sen-
sor.>

Step

Check

Yes

No

EN(H6DO)(diag)-166

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AT:DTC P0175 SYSTEM TOO RICH (BANK 2)

DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.
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.>.

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 EGR VALVE.

Is the EGR valve stuck?

Replace the EGR 
valve.

Go to step 4.

4

CHECK PURGE CONTROL SOLENOID 
VALVE.

Is the purge control solenoid 
valve stuck?

Replace the purge 
control solenoid 
valve.

Go to step 5.

5

CHECK PCV VALVE.

Is the PCV valve stuck?

Replace the PCV 
valve.

Go to step 6.

6

CHECK FUEL PRESSURE.

Warning:

• Place “NO FIRE” signs near the working 
area.
• Be careful not to spill fuel.

1) Release the fuel pressure.

(1) Disconnect the connector from fuel 
pump relay.
(2) Start the engine and run until it stalls.
(3) After the engine stalls, crank it for five 
more seconds.
(4) Turn the ignition switch to OFF.

2) Connect the connector to fuel pump relay.
3) Disconnect the fuel delivery hose, and con-
nect the fuel pressure gauge.
4) Install the fuel filler cap.
5) Start the engine and idle while gear posi-
tion is neutral.
6) Measure the fuel pressure while discon-
necting pressure regulator vacuum hose from 
intake manifold.

Warning:

Release fuel pressure before removing the
fuel pressure gauge.

NOTE:

If fuel pressure does not increase, squeeze fuel
return hose 2 to 3 times, then measure fuel
pressure again.

Is fuel pressure 333 — 363 

kPa (3.4 — 3.7 kgf/cm

2

, 48 — 

53 psi)?

Go to step 7.

Repair the follow-
ing items.
Fuel pressure is 
too high:

• Clogged fuel 
return line or 
bent hose

Fuel pressure is 
too low:

• Improper fuel 
pump discharge
• Clogged fuel 
supply line

EN(H6DO)(diag)-167

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

7

CHECK FUEL PRESSURE.
After connecting the pressure regulator vac-
uum hose, measure fuel pressure.

Warning:

Release fuel pressure before removing the
fuel pressure gauge.

NOTE:

• If fuel pressure does not increase, squeeze 
fuel return hose 2 to 3 times, then measure 
fuel pressure again.
• If the measured value at this step is out of 
specifications, check or replace pressure regu-
lator and pressure regulator vacuum hose.

Is fuel pressure 279 — 309 

kPa (2.85 — 3.15 kgf/cm

2

, 40 

— 45 psi)?

Go to step 8.

Repair the follow-
ing items.
Fuel pressure is 
too high:

• Faulty pres-
sure regulator
• Clogged fuel 
return line or 
bent hose

Fuel pressure is 
too low:

• Faulty pres-
sure regulator
• Improper fuel 
pump discharge
• Clogged fuel 
supply line

8

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)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the engine coolant tempera-
ture 70 — 100

°C (158 — 

212

°F)?

Go to step 9.

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H6DO)-18, 
Engine Coolant 
Temperature Sen-
sor.>

9

CHECK MANIFOLD PRESSURE SENSOR 
SIGNAL.
1) Start and warm-up the engine until engine 
coolant temperature is above 60

°C (140°F).

2) Place the select lever in “N” or “P” position.
3) Turn the A/C switch to OFF.
4) Turn all the accessory switches to OFF.
5) Read the data of manifold absolute pres-
sure sensor signal using Subaru Select Moni-
tor 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 measurement value 24.0 
— 41.3 kPa (180 — 310 
mmHg, 7.09 — 12.20 inHg) 
when idling and 73.3 — 106.6 
kPa (550 — 800 mmHg, 21.65 
— 31.50 inHg) when the igni-
tion turns to ON?

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

Replace the mani-
fold absolute pres-
sure sensor. <Ref. 
to FU(H6DO)-23, 
Manifold Absolute 
Pressure Sensor.>

Step

Check

Yes

No

EN(H6DO)(diag)-168

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AU:DTC P0197 ENGINE OIL TEMPERATURE SENSOR LOW

DTC DETECTING CONDITION:
Immediately at fault recognition
TROUBLE SYMPTOM:
• Hard to start
• Erroneous idling
• 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-03500

E75

E2

B21

B136

ECM

B83

1

19

35

E1

B20

2

3

27

*

  : TERMINAL No. 
    RANDOM ARRANGEMENT

*

*

E75

1 2

B20

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B21

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 3 4
5 6 7 8

B83

OIL 

TEMPERATURE

SENSOR