Subaru Legacy IV (2008 year). Manual — part 373

EN(H4DOTC)(diag)-313

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 DTC using
“List of Diagnostic
Trouble Code
(DTC)”. <Ref. to
EN(H4DOTC)(diag)
-81, List of Diag-
nostic Trouble
Code (DTC).>

Go to step 2.

2

CHECK FRONT OXYGEN (A/F) SENSOR
CONNECTOR AND COUPLING CONNEC-
TOR.

Has water entered the connec-
tor?

Completely
remove any water
inside.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and
front oxygen (A/F) sensor.
3) Measure the resistance of harness between
ECM and front oxygen (A/F) sensor connector.

Connector & terminal

(B135) No. 9 — (E79) No. 1:
(B135) No. 8 — (E79) No. 3:

Is the resistance less than 1

:? Go to step 4.

Repair the harness
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and front oxy-
gen (A/F) sensor
connector
• Poor contact of
coupling connector

4

CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure the resistance between ECM and
chassis ground.

Connector & terminal

(B135) No. 9 — Chassis ground:
(B135) No. 8 — Chassis ground:

Is the resistance 1 M

: or

more?

Go to step 5.

Repair the ground
short circuit of har-
ness between
ECM and front oxy-
gen (A/F) sensor
connector.

5

CHECK OUTPUT SIGNAL FOR ECM.
1) Connect the ECM.
2) Turn the ignition switch to ON.
3) Measure the voltage between front oxygen
(A/F) sensor connector and chassis ground.

Connector & terminal

(E79) No. 1 (+) — Chassis ground (–):

Is the voltage 4.5 V or more?

Go to step 7.

Go to step 6.

6

CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between front oxygen (A/F)
sensor connector and chassis ground.

Connector & terminal

(E79) No. 3 (+) — Chassis ground (–):

Is the voltage 4.95 V or more?

Go to step 7.

Go to step 8.

7

CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between front oxygen (A/F)
sensor connector and chassis ground.

Connector & terminal

(E79) No. 1 (+) — Chassis ground (–):
(E79) No. 3 (+) — Chassis ground (–):

Is the voltage 8 V or more?

Repair the short
circuit to power in
the harness
between ECM and
front oxygen (A/F)
sensor connector.
After repair,
replace the ECM.
<Ref. to
FU(H4DOTC)-52,
Engine Control
Module (ECM).>

Repair the poor
contact of ECM
connector.

8

CHECK EXHAUST SYSTEM.

Are there holes or loose bolts
on exhaust system?

Repair the exhaust
system.

Go to step 9.

EN(H4DOTC)(diag)-314

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

9

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 10.

10

CHECK FUEL PRESSURE.

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

CAUTION:
Be careful not to spill fuel.
1) Connect the front oxygen (A/F) sensor con-
nector.
2) Measure the fuel pressure while discon-
necting pressure regulator vacuum hose from
intake manifold. <Ref. to ME(H4DOTC)-25,
INSPECTION, Fuel Pressure.>

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

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

Is the measured value 284 —
314 kPa (2.9 — 3.2 kgf/cm

2

,

41 — 46 psi)?

Go to step 11.

Repair the follow-
ing item.
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

11

CHECK FUEL PRESSURE.
After connecting the pressure regulator vacuum
hose, measure fuel pressure. <Ref. to
ME(H4DOTC)-25, INSPECTION, Fuel Pres-
sure.>

CAUTION:
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 regula-
tor and pressure regulator vacuum hose.

Is the measured value 230 —
260 kPa (2.35 — 2.65 kgf/cm

2

,

33 — 38 psi)?

Go to step 12.

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

12

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(H4DOTC)(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 13.

Replace the
engine coolant
temperature sen-
sor. <Ref. to
FU(H4DOTC)-31,
Engine Coolant
Temperature Sen-
sor.>

Step

Check

Yes

No

EN(H4DOTC)(diag)-315

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

13

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) For AT models, set the select lever to “P”
range or “N” range, and for MT models, place
the shift lever in the neutral position.
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(H4DOTC)(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/s) ?

Go to step 14.

Replace the mass
air flow and intake
air temperature
sensor. <Ref. to
FU(H4DOTC)-36,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>

14

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) For AT models, set the select lever to “P”
range or “N” range, and for MT models, place
the shift lever in the neutral position.
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(H4DOTC)(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)?

Go to step 15.

Check the mass air
flow and intake air
temperature sen-
sor. <Ref. to
FU(H4DOTC)-36,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>

Step

Check

Yes

No

EN(H4DOTC)(diag)-316

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

15

CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is above 75°C (167°F), and keep
the engine speed at 3,000 rpm. (for up to 2 min-
utes)
2) Read the data of rear oxygen sensor signal
using Subaru Select Monitor or general scan
tool.

NOTE:
• Depress the clutch pedal. (MT model)
• Subaru Select Monitor
For detailed operation procedure, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4DOTC)(diag)-34, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the voltage 490 mV or more? Go to step 16.

Go to step 17.

16

CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is above 75°C (167°F), and rapidly
reduce the engine speed from 3,000 rpm.
2) Read the data of rear oxygen sensor signal
using Subaru Select Monitor or general scan
tool.

NOTE:
• Depress the clutch pedal. (MT model)
• Subaru Select Monitor
For detailed operation procedure, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4DOTC)(diag)-34, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the voltage 250 mV or less?

Go to step 18.

Go to step 17.

17

CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.

Has water entered the connec-
tor?

Completely
remove any water
inside.

Go to step 19.

18

CHECK FRONT OXYGEN (A/F) SENSOR
AND REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is higher than 75°C (167°F), then
keep the engine idling for 5 minutes or more.
2) Read the data of rear oxygen 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(H4DOTC)(diag)-34, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is a voltage of 0.8 V or more
maintained for 5 minutes or
more?

Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4DOTC)-46,
Front Oxygen (A/F)
Sensor.>

Go to step 19.

Step

Check

Yes

No