Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 296

EN(H4DOTC)(diag)-408

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

CHECK ENGINE COOLANT TEMPERATURE
SENSOR.
1) Start the engine and warm up completely.
2) Read the value of «Coolant Temp.» using
the Subaru Select Monitor or a general scan
tool.
NOTE:

• Subaru Select Monitor
For detailed operation procedures, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4DOTC)(diag)-40, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the value of «Coolant
Temp.» 75°C (167°F) or more?

Go to step

12.

Replace the
engine coolant
temperature sen-
sor. <Ref. to
FU(STI)-34,
Engine Coolant
Temperature Sen-
sor.> <Ref. to
FU(w/o STI)-34,
Engine Coolant
Temperature Sen-
sor.>

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 shift lever in neutral position.
3) Turn the A/C switch to OFF.
4) Turn all the accessory switches to OFF.
5) Read the value of «Mass Air Flow» using
the Subaru Select Monitor or a general scan
tool.
NOTE:

Is the value of «Mass Air
Flow» 2.0 — 5.0 g/s (0.26 —
0.66 lb/m)?

Go to step

13.

Replace the mass
air flow and intake
air temperature
sensor. <Ref. to
FU(STI)-42, Mass
Air Flow and Intake
Air Temperature
Sensor.> <Ref. to
FU(w/o STI)-42,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>

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 shift lever in 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 value of «Intake Air Temp.» using
the Subaru Select Monitor or a general scan
tool.
NOTE:

Subtract ambient temperature
from «Intake Air Temp.». Is the
obtained value –10 — 50°C (–18
— 90°F)?

Go to step

14.

Check the mass air
flow and intake air
temperature sen-
sor. <Ref. to
FU(STI)-42, Mass
Air Flow and Intake
Air Temperature
Sensor.> <Ref. to
FU(w/o STI)-42,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>

Step

Check

Yes

EN(H4DOTC)(diag)-409

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is higher than 75°C (167°F), and
keep the engine speed at 3,000 rpm. (2 minutes
maximum)
2) Read the value of «Rear O2 Sensor» using
the Subaru Select Monitor or a general scan
tool.
NOTE:

• Depress the clutch pedal.
• Subaru Select Monitor
For detailed operation procedures, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4DOTC)(diag)-40, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the value of «Rear O2 Sen-
sor» 0.490 V or more?

CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is higher than 75°C (167°F), and
rapidly reduce the engine speed from 3,000
rpm.
2) Read the value of «Rear O2 Sensor» using
the Subaru Select Monitor or a general scan
tool.
NOTE:

Is the value of «Rear O2 Sen-
sor» 0.250 V or less?

CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.

Has water entered the connec-
tor?

Completely
remove any water
inside.

Go to step

18.

CHECK FRONT OXYGEN (A/F) SENSOR US-
ING REAR OXYGEN SENSOR SIGNAL.
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 value of «Rear O2 Sensor» using
the Subaru Select Monitor or a general scan
tool.
NOTE:

Is the value in «Rear O2 Sen-
sor» kept at 0.250 V or less for
5 minutes or more?

Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(STI)-54, Front
Oxygen (A/F) Sen-
sor.> <Ref. to
FU(w/o STI)-53,
Front Oxygen (A/F)
Sensor.>

Go to step

18.

Step

Check

Yes

EN(H4DOTC)(diag)-410

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

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

Connector & terminal

(B136) No. 20 — (T6) No. 3:
(B135) No. 30 — (T6) No. 4:

Is the resistance less than 1 Ω? Go to step

19.

Repair the harness
and connector.
NOTE:

In this case, repair
the following item:
• Open circuit in
harness between
ECM

connector

and rear oxygen
sensor connector
• Poor contact of
coupling connector

CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Connect the connector to ECM.
2) Turn the ignition switch to ON.
3) Measure the voltage between rear oxygen
sensor connector and chassis ground.

Connector & terminal

(T6) No. 3 (+) — Chassis ground (–):

Is the voltage 0.2 — 0.5 V?

Replace the rear
oxygen sensor.
<Ref. to FU(STI)-
56, Rear Oxygen
Sensor.> <Ref. to
FU(w/o STI)-55,
Rear Oxygen Sen-
sor.>

Go to step

20.

CHECK OUTPUT SIGNAL OF ECM.
1) Turn the ignition switch to ON.
2) Measure the voltage between ECM and
chassis ground on faulty cylinders.

Connector & terminal

#1 (B134) No. 10 (+) — Chassis ground (–):
#2 (B134) No. 11 (+) — Chassis ground (–):
#3 (B134) No. 12 (+) — Chassis ground (–):
#4 (B134) No. 13 (+) — Chassis ground (–):

Is the voltage 10 V or more?

CHECK HARNESS BETWEEN ECM AND
FUEL INJECTOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from fuel injector
on faulty cylinders.
3) Measure the resistance between fuel injec-
tor connector and engine ground on faulty cylin-
ders.

Connector & terminal

#1 (E5) No. 2 — Engine ground:
#2 (E16) No. 2 — Engine ground:
#3 (E6) No. 2 — Engine ground:
#4 (E17) No. 2 — Engine ground:

Is the resistance 1 MΩ or
more?

Go to step

22.

Repair the short
circuit to ground in
harness between
ECM connector
and fuel injector
connector.

CHECK HARNESS BETWEEN ECM AND
FUEL INJECTOR CONNECTOR.
Measure the resistance of harness between
ECM and fuel injector connector on faulty cylin-
ders.

Connector & terminal

#1 (B134) No. 10 — (E5) No. 2:
#2 (B134) No. 11 — (E16) No. 2:
#3 (B134) No. 12 — (E6) No. 2:
#4 (B134) No. 13 — (E17) No. 2:

Is the resistance less than 1 Ω? Go to step

23.

Repair the harness
and connector.
NOTE:

In this case, repair
the following item:
• Open circuit in
harness between
ECM

connector

and fuel injector
connector
• Poor contact of
coupling connector

Step

Check

Yes

EN(H4DOTC)(diag)-411

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

CHECK FUEL INJECTOR.
Measure the resistance between fuel injector
terminals on faulty cylinder.

Terminals

No. 1 — No. 2:

Is the resistance 5 — 20 Ω?

Go to step

24.

Replace the faulty
fuel injector. <Ref.
to FU(STI)-45,
Fuel Injector.>
<Ref. to FU(w/o
STI)-45, Fuel
Injector.>

CHECK POWER SUPPLY LINE.
1) Turn the ignition switch to ON.
2) Measure the voltage between fuel injector
connector of faulty cylinders and engine
ground.

Connector & terminal

#1 (E5) No. 1 (+) — Engine ground (–):
#2 (E16) No. 1 (+) — Engine ground (–):
#3 (E6) No. 1 (+) — Engine ground (–):
#4 (E17) No. 1 (+) — Engine ground (–):

Is the voltage 10 V or more?

Repair the poor
contact of all con-
nectors in fuel
injector circuit.

Repair the harness
and connector.
NOTE:

In this case, repair
the following item:
• Open circuit in
harness between
the main relay and
fuel injector con-
nector on faulty
cylinders
• Poor contact of
coupling connector
• Poor contact of
main relay connec-
tor

CHECK HARNESS BETWEEN ECM AND
FUEL INJECTOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from fuel injector
on faulty cylinders.
3) Turn the ignition switch to ON.
4) Measure the voltage between ECM and
chassis ground on faulty cylinders.

Connector & terminal

#1 (B134) No. 10 (+) — Chassis ground (–):
#2 (B134) No. 11 (+) — Chassis ground (–):
#3 (B134) No. 12 (+) — Chassis ground (–):
#4 (B134) No. 13 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Repair the short
circuit to power in
harness between
ECM connector
and fuel injector
connectors.

Go to step

26.

CHECK FUEL INJECTOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance between fuel injec-
tor terminals on faulty cylinder.

Terminals

No. 1 — No. 2:

Is the resistance 5 — 20 Ω?

Go to step

27.

Replace the faulty
fuel injector. <Ref.
to FU(STI)-45,
Fuel Injector.>
<Ref. to FU(w/o
STI)-45, Fuel
Injector.>

CHECK INSTALLATION CONDITION OF
CAMSHAFT POSITION SENSOR/CRANK-
SHAFT POSITION SENSOR.