Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Manual — part 242

EN(H4DOTC)(diag)-192

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

BE:DTC P0300 RANDOM/MULTIPLE CYLINDER MISFIRE DETECTED

DTC DETECTING CONDITION:

• Detected when 2 consecutive driving cycles with fault occur.

• Immediately at fault recognition (A misfire which could damage catalyst occurs.)

• GENERAL DESCRIPTION <Ref. to GD(H4DOTC)-113, DTC P0300 RANDOM/MULTIPLE CYLINDER

MISFIRE DETECTED, Diagnostic Trouble Code (DTC) Detecting Criteria.>

TROUBLE SYMPTOM:

• Engine stalls.

• Improper idling

• Rough driving
CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Mode <Ref. to EN(H4DOTC)(diag)-63,

OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4DOTC)(diag)-49, PROCE-

DURE, Inspection Mode.>.

EN(H4DOTC)(diag)-193

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

WIRING DIAGRAM:

• Engine electrical system, without SI-DRIVE <Ref. to WI-32, WITHOUT SI-DRIVE, WIRING DIAGRAM,

Engine Electrical System.>

• Engine electrical system, with SI-DRIVE <Ref. to WI-48, WITH SI-DRIVE, WIRING DIAGRAM, Engine

Electrical System.>

Step

Check

Yes

No

1

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

Connector & terminal

#1 (B137) No. 8 (+) — Chassis ground (–):
#2 (B137) No. 9 (+) — Chassis ground (–):
#3 (B137) No. 10 (+) — Chassis ground (–):
#4 (B137) No. 11 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step

6.

Go to step

2.

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)-194

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

2

CHECK HARNESS BETWEEN ECM AND
FUEL INJECTOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from all fuel injec-
tors.
3) Measure the resistance between all fuel
injector connectors 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 resistance 1 MΩ or
more?

Go to step

3.

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

3

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

Connector & terminal

#1 (B137) No. 8 — (E5) No. 1:
#2 (B137) No. 9 — (E16) No. 1:
#3 (B137) No. 10 — (E6) No. 1:
#4 (B137) No. 11 — (E17) No. 1:

Is the resistance less than 1 Ω? Go to step

4.

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

4

CHECK FUEL INJECTOR.
Measure the resistance between all fuel injector
terminals.

Terminals

No. 1 — No. 2:

Is the resistance 5 — 20 Ω?

Go to step

5.

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

5

CHECK POWER SUPPLY LINE.
1) Turn the ignition switch to ON.
2) Measure the voltage between all fuel injec-
tor connectors and the engine ground.

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 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 con-
nector and fuel in-
jector connector on
faulty cylinders
• Poor contact of
coupling connector
• Poor contact of
main relay connec-
tor

6

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

Connector & terminal

#1 (B137) No. 8 (+) — Chassis ground (–):
#2 (B137) No. 9 (+) — Chassis ground (–):
#3 (B137) No. 10 (+) — Chassis ground (–):
#4 (B137) No. 11 (+) — 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

7.

Step

Check

Yes

No

EN(H4DOTC)(diag)-195

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

7

CHECK FUEL INJECTOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance between all fuel
injector terminals.

Terminals

No. 1 — No. 2:

Is the resistance 5 — 20 Ω?

Go to step

8.

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

8

CHECK INSTALLATION OF CAMSHAFT PO-
SITION SENSOR/CRANKSHAFT POSITION
SENSOR.

Is the camshaft position sensor
or crankshaft position sensor
loosely installed?

Tighten the cam-
shaft position sen-
sor or crankshaft
position sensor.
<Ref. to FU(STI)-
37, Camshaft Posi-
tion Sensor.>
<Ref. to FU(STI)-
35, Crankshaft
Position Sensor.>
<Ref. to FU(w/o
STI)-37, Camshaft
Position Sensor.>
<Ref. to FU(w/o
STI)-35, Crank-
shaft Position Sen-
sor.>

Go to step

9.

9

CHECK CRANK SPROCKET.
Remove the timing belt cover.

Is the crank sprocket rusted or
does it have broken teeth?

Replace the crank
sprocket. <Ref. to
ME(STI)-60, Crank
Sprocket.> <Ref. to
ME(w/o STI)-58,
Crank Sprocket.>

Go to step

10.

10

CHECK INSTALLATION CONDITION OF
TIMING BELT.
Turn the crankshaft, and align alignment mark
on crank sprocket with alignment mark on cylin-
der block.
ST 499987500

CRANKSHAFT
SOCKET

Is the timing belt dislocated
from its proper position?

Repair the installa-
tion condition of
timing belt. <Ref.
to ME(STI)-50,
Timing Belt.> <Ref.
to ME(w/o STI)-48,
Timing Belt.>

Go to step

11.

11

CHECK FUEL LEVEL.

Is the fuel meter indication
higher than the “Lower” level?

Go to step

12.

Refill the fuel so
that the fuel meter
indication is higher
than the “Lower”
level, and proceed
to the next step.
Go to step

12.

12

CHECK STATUS OF MALFUNCTION INDI-
CATOR LIGHT.
1) Clear the memory using the Subaru Select
Monitor or general scan tool. <Ref. to
EN(H4DOTC)(diag)-63, Clear Memory Mode.>
2) Start the engine, and drive the vehicle 10
minutes or more.

Does the malfunction indicator
light illuminate or blink?

Go to step

14.

Go to step

13.

Step

Check

Yes

No