Subaru Legacy (2005 year). Manual - part 212

EN(H4SO 2.5)(diag)-133

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK OPTION CODE.

Is the option code EC, EK, EH, 
ER or K4?

Go to step 2.

Refer to EN(H4SO 
2.0) section. <Ref. 
to EN(H4SO 
2.0)(diag)-64, List 
of Diagnostic Trou-
ble Code (DTC).>

NOTE:
Fuel injection sys-
tem for KA and KS
model is the same
as 2.0 L model.

2

CHECK ANY OTHER DTC ON DISPLAY.

Is any other DTC displayed?

Inspect the rele-
vant DTC using 
“List of Diagnostic 
Trouble Code 
(DTC)”. <Ref. to 
EN(H4SO 
2.5)(diag)-69, List 
of Diagnostic Trou-
ble Code (DTC).>

NOTE:
In this case, it is
not necessary to
inspect DTC
P0139.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and 
rear oxygen sensor.
3) Measure the resistance of harness 
between ECM and rear oxygen sensor con-
nector.

Connector & terminal

(B137) No. 24 — (B19) No. 3:

Is the resistance less than 1 
Ω?

Go to step 4.

Repair open circuit 
in harness 
between ECM and 
rear oxygen sen-
sor connector.

4

CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
Measure the resistance between rear oxygen 
sensor harness connector and chassis ground.

Connector & terminal

(B19) No. 3 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 5.

Repair short circuit 
to ground in har-
ness.

5

CHECK REAR OXYGEN SENSOR DATA.
Measure the resistance between connector 
terminals of rear oxygen sensor.

Terminals

No. 3 — No. 4:

Is the resistance less than 1 
Ω?

Replace the rear 
oxygen sensor. 
<Ref. to FU(H4SO 
2.5)-36, Rear Oxy-
gen Sensor.>

A temporary poor 
compact occurs. 
Check poor con-
tact in connector.

EN(H4SO 2.5)(diag)-134

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

X: DTC P0171 SYSTEM TOO LEAN (BANK 1)

Refer to DTC P0172 for diagnostic procedure. <Ref. to EN(H4SO 2.5)(diag)-134, DTC P0172 SYSTEM TOO
RICH (BANK 1), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

Y: DTC P0172 SYSTEM TOO RICH (BANK 1)

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(H4SO 2.5)(diag)-
40, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.5)(diag)-33, Inspection Mode.>.

Step

Check

Yes

No

1

CHECK OPTION CODE.

Is the option code EC, EK, EH, 
ER or K4?

Go to step 2.

Refer to EN(H4SO 
2.0) section. <Ref. 
to EN(H4SO 
2.0)(diag)-64, List 
of Diagnostic Trou-
ble Code (DTC).>

NOTE:
Fuel injection sys-
tem for KA and KS
model is the same
as 2.0 L model.

2

CHECK EXHAUST SYSTEM.

Are there holes or loose bolts 
on exhaust system?

Repair the exhaust 
system.

Go to step 3.

3

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 4.

4

CHECK EGR VALVE.

Is the EGR valve stuck?

Replace the EGR 
valve.

Go to step 5.

5

CHECK PURGE CONTROL SOLENOID 
VALVE.

Is the purge control solenoid 
valve stuck?

Replace the purge 
control solenoid 
valve.

Go to step 6.

6

CHECK PCV VALVE.

Is the PCV valve stuck?

Replace the PCV 
valve.

Go to step 7.

EN(H4SO 2.5)(diag)-135

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

7

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 284 — 314 

kPa (2.9 — 3.2 kgf/cm

2

, 41 — 

46 psi)?

Go to step 8.

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

8

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 
specification, check or replace pressure regu-
lator and pressure regulator vacuum hose.

Is fuel pressure 206 — 235 

kPa (2.1 — 2.4 kgf/cm

2

, 30 — 

34 psi)?

Go to step 9.

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

9

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(H4SO 2.5)(diag)-25, Subaru Select 
Monitor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the engine coolant tempera-
ture 70

°C (158°F) — 100°C 

(212

°F)?

Go to step 10.

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H4SO 2.5)-20, 
Engine Coolant 
Temperature Sen-
sor.>

Step

Check

Yes

No

EN(H4SO 2.5)(diag)-136

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Z: DTC P0222 THROTTLE/PEDAL POSITION SENSOR/SWITCH “B” CIRCUIT 

LOW

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

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H4SO 2.5)(diag)-
40, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.5)(diag)-33, Inspection Mode.>.

10

CHECK MANIFOLD ABSOLUTE 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(H4SO 2.5)(diag)-25, Subaru Select 
Monitor.>
• 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 ignition 
turned ON?

Replace the ECM. 
<Ref. to FU(H4SO 
2.5)-37, Engine 
Control Module 
(ECM).>

Replace the mani-
fold absolute pres-
sure sensor. <Ref. 
to FU(H4SO 2.5)-
25, Manifold Abso-
lute Pressure Sen-
sor.>

Step

Check

Yes

No