Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Manual — part 295

EN(H4DOTC)(diag)-404

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

ECM

6

4 5

3

2

1

*

2

1

B220

15A

9

10

11
12

B220

*

*

1 2
3 4

D1

36

D3 A4

40

34

35

B21

E2

A6

A3

B220

13
14

15 16

17

27

24

25
26

20

21
22

23

29
30

31

28

32 35

33
34

37
38

39

36

40

8

9

10

11 12

1

2

5

3

4

7

6

19

18

B134

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

A:

D: B137

C: B136

B: B135

A:

T6

B134

C9

B30

C20

B6

*

*

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

4

1

3

4

1

3

B19

T5

22

T5

B19

5

6

7

8

2

1

9

4

3

10

22 23

11 12 13 14 15

24 25

26

16 17

18 19 20 21

27

28 29

30 31

B135

B:

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

B136

C:

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

D: B137

B19

T6

B83

B138

B138

B83

EN-08723

SBF-5

E

E

BATTERY

: TERMINAL No. OPTIONAL ARRANGEMENT

REAR

OXYGEN SENSOR

A/F, OXYGEN SENSOR

RELAY

FUSE

(RELAY BLOCK)

EN(H4DOTC)(diag)-405

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

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

2.

2

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 connector and front oxygen (A/F) sensor
connector.

Connector & terminal

Models without SI-DRIVE

(B136) No. 19 — (E22) No. 1:
(B136) No. 18 — (E22) No. 3:

Models with SI-DRIVE

(B136) No. 19 — (B379) No. 4:
(B136) No. 18 — (B379) No. 3:

Is the resistance less than 1 Ω? Go to step

3.

Repair the harness
and connector.
NOTE:

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

connector

and front oxygen
(A/F) sensor con-
nector
• Poor contact of
coupling connector

ECM

EN-08718

#4

2

1

#3

2

1

#2

2

1

B21

#1

2

1

4

8

54

53

52

51

10

11

12

13

1 2

B21

E5

E5

E2

E6

E6

E16

E16

E17

E17

B134

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

B220

24

23

22

15A

B220

3

4

21

B134

31

30

32

29

34

33

21

20

19

18

17

16

28

27

26

15

14

13

12

11

25

23

22

24

10

3

4

9

1

2

8

7

6

5

B220

18

19

6

7

4

3
5

2

1

12

11

10

9

8

40

36 39

38

37

34

33

35

32

28 31

30

29

23

22

21

20

26

25

24

27

17

16

15

14

13

E

SBF-7

MAIN RELAY

FUSE

(RELAY BLOCK)

FUEL INJECTOR

BATTERY

EN(H4DOTC)(diag)-406

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

3

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

Connector & terminal

(B136) No. 19 — Chassis ground:
(B136) No. 18 — Chassis ground:

Is the resistance 1 MΩ or
more?

Go to step

4.

Repair the short
circuit to ground in
harness between
ECM connector
and front oxygen
(A/F) sensor con-
nector.

4

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

Connector & terminal

Models without SI-DRIVE

(E22) No. 1 (+) — Chassis ground (–):

Models with SI-DRIVE

(B379) No. 4 (+) — Chassis ground (–):

Is the voltage 4.5 V or more?

Go to step

6.

Go to step

5.

5

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

Connector & terminal

Models without SI-DRIVE

(E22) No. 3 (+) — Chassis ground (–):

Models with SI-DRIVE

(B379) No. 3 (+) — Chassis ground (–):

Is the voltage 4.95 V or more? Go to step

6.

Go to step

7.

6

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

Connector & terminal

Models without SI-DRIVE

(E22) No. 3 (+) — Chassis ground (–):
(E22) No. 1 (+) — Chassis ground (–):

Models with SI-DRIVE

(B379) No. 3 (+) — Chassis ground (–):
(B379) No. 4 (+) — Chassis ground (–):

Is the voltage 8 V or more?

Repair the short
circuit to power in
the harness
between ECM con-
nector and front
oxygen (A/F) sen-
sor connector.
After repair,
replace the ECM.
<Ref. to FU(STI)-
59, Engine Control
Module (ECM).>
<Ref. to FU(w/o
STI)-57, Engine
Control Module
(ECM).>

Repair the poor
contact of ECM
connector.

7

CHECK EXHAUST SYSTEM.

Are there holes or loose bolts
on exhaust system?

Repair the exhaust
system.

Go to step

8.

8

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

9.

Step

Check

Yes

No

EN(H4DOTC)(diag)-407

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

9

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(STI)-25, INSPEC-
TION, Fuel Pressure.> <Ref. to ME(w/o STI)-
24, 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 kg/cm

2

, 41

— 46 psi)?

Go to step

10.

Check the fuel
pump and fuel
delivery line.
• Models without
SI-DRIVE <Ref. to
FU(w/o STI)-79,
INSPECTION,
Fuel Pump.> <Ref.
to FU(w/o STI)-93,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>
• Models with SI-
DRIVE <Ref. to
FU(STI)-81,
INSPECTION,
Fuel Pump.> <Ref.
to FU(STI)-97,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>

10

CHECK FUEL PRESSURE.
After connecting the pressure regulator vacuum
hose, measure fuel pressure. <Ref. to ME(STI)-
25, INSPECTION, Fuel Pressure.> <Ref. to
ME(w/o STI)-24, 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 vacuum hose.

Is the measured value 230 —
260 kPa (2.4 — 2.7 kg/cm

2

, 33

— 38 psi)?

Go to step

11.

Check the fuel
pump and fuel
delivery line.
• Models without
SI-DRIVE <Ref. to
FU(w/o STI)-79,
INSPECTION,
Fuel Pump.> <Ref.
to FU(w/o STI)-93,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>
• Models with SI-
DRIVE <Ref. to
FU(STI)-81,
INSPECTION,
Fuel Pump.> <Ref.
to FU(STI)-97,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>

Step

Check

Yes

No