ENGINE (DIAGNOSTICS)(H4SO) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0304 CYLINDER 4 MISFIRE DETECTED

DTC DETECTING CONDITION:

• Detected when two consecutive driving cycles with fault occur.

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

TROUBLE SYMPTOM:

• Engine stalls.

• Erroneous idling

• Rough driving

CAUTION:

After repair or replacement of faulty parts, perform Clear Memory Mode and Inspection Mode .

WIRING DIAGRAM:

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1.CHECK ANY OTHER DTC ON DISPLAY.

Is there any other DTC displayed?

Check DTC using “List of Diagnostic Trouble Code (DTC)”.

2.CHECK OUTPUT SIGNAL OF ECM.

1) Turn the ignition switch to ON.

2) Measure the voltage between ECM connector and chassis ground on faulty 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?

3.CHECK HARNESS BETWEEN FUEL INJECTOR AND ECM CONNECTOR.

1) Turn the ignition switch to OFF.

2) Disconnect the connector from fuel injector on faulty cylinders.

3) Disconnect the connectors from the ECM.

4) Measure the resistance between ECM connector and engine ground on faulty cylinders.

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?

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

4.CHECK HARNESS BETWEEN FUEL INJECTOR AND ECM CONNECTOR.

Measure the resistance of harness connector between ECM connector and fuel injector on faulty cylinders.

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?

Repair the harness and connector.

NOTE:

In this case, repair the following item:

• Open circuit of harness between ECM and fuel injector connector

• Poor contact of coupling connector

5.CHECK FUEL INJECTOR.

Measure the resistance between fuel injector terminals on faulty cylinder.

Terminals

No. 1 — No. 2:

Is the resistance between 5 — 20 Ω?

Replace the faulty fuel injector.

6.CHECK POWER SUPPLY LINE.

1) Turn the ignition switch to ON.

2) Measure the voltage between fuel injector and engine ground on faulty cylinders.

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 connectors in fuel injector circuit.

Repair the harness and connector.

NOTE:

In this case, repair the following item:

• Open circuit in harness between main relay and fuel injector connector on faulty cylinders

• Poor contact of coupling connector

• Poor contact of main relay connector

• Poor contact of fuel injector connector on faulty cylinders

7.CHECK HARNESS BETWEEN FUEL INJECTOR AND ECM 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 connector and chassis ground on faulty 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 battery short circuit of harness between ECM and fuel injector. After repair, replace the ECM.

8.CHECK FUEL INJECTOR.

1) Turn the ignition switch to OFF.

2) Measure the resistance between fuel injector terminals on faulty cylinder.

Terminals

No. 1 — No. 2:

Is the resistance less than 1 Ω?

Replace the faulty fuel injector and ECM.

9.CHECK INSTALLATION OF CAMSHAFT POSITION SENSOR/CRANKSHAFT POSITION SENSOR.

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

Tighten the camshaft position sensor or crankshaft position sensor.

10.CHECK CRANK SPROCKET.

Remove the timing belt cover.

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

Replace the crank sprocket.

11.CHECK INSTALLATION CONDITION OF TIMING CHAIN.

Turn the crankshaft, and align alignment mark on crank sprocket with alignment mark on cylinder block.

Is the timing chain dislocated from its proper position?

Repair the installation condition of timing chain.

12.CHECK FUEL LEVEL.

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

Replenish fuel so fuel meter indication is higher than the “Lower” level. After filling fuel,

13.CHECK STATUS OF MALFUNCTION INDICATOR LIGHT.

1) Perform the Clear Memory Mode using Subaru Select Monitor.

2) Start the engine, and drive the vehicle 10 minutes or more.

Does the malfunction indicator light illuminate or blink?

14.CHECK CAUSE OF MISFIRE.

Has the cause of misfire been detected while running the engine? Ex.: Disconnection of spark plug cord

Finish diagnostics operation, if the engine has no abnormality.

Repair the poor contact.

NOTE:

In this case, repair the following item:

• Poor contact of ignition coil connector

• Poor contact of fuel injector connector on faulty cylinders

• Poor contact in ECM connector

• Poor contact of coupling connector

15.CHECK AIR INTAKE SYSTEM.

Is there any fault in air intake system?

Repair the air intake system.

NOTE:

Check the following items.

• Are there air leaks or air suction caused by loose or dislocated nuts and bolts?

• Are there cracks or any disconnection of hoses?

16.CHECK MISFIRE SYMPTOM.

1) Turn the ignition switch to ON.

2) Read the DTC.

• Subaru Select Monitor

NOTE:

Perform the diagnosis according to following items.

Does the Subaru Select Monitor display only one DTC?

17.CHECK ANY OTHER DTC ON DISPLAY.

Are DTCs P0301 and P0302 displayed?

18.CHECK DTC ON DISPLAY.

Are DTCs P0303 and P0304 displayed?

19.CHECK DTC ON DISPLAY.

Are DTCs P0301 and P0303 displayed?

20.CHECK DTC ON DISPLAY.

Are DTCs P0302 and P0304 displayed?

21.ONLY ONE CYLINDER.

Is there any fault in the cylinder?

Repair or replace faulty parts.

NOTE:

Check the following items.

• Spark plug

• Spark plug cord

• Fuel injector

• Compression ratio

Go to DTC P0171.

22.GROUP OF #1 AND #2 CYLINDERS.

Are there any faults in #1 and #2 cylinders?

Repair or replace faulty parts.

NOTE:

Check the following items.

• Spark plug

• Fuel injector

• Ignition coil

• Compression ratio

If any fault are not found, check the “IGNITION CONTROL SYSTEM” of #1 and #2 cylinders side.

Go to DTC P0171.

23.GROUP OF #3 AND #4 CYLINDERS.

Are there any faults in #3 and #4 cylinders?

Repair or replace faulty parts.

NOTE:

Check the following items.

• Spark plug

• Fuel injector

• Ignition coil

If any fault are not found, check the “IGNITION CONTROL SYSTEM” of #3 and #4 cylinders side.

Go to DTC P0171.

24.GROUP OF #1 AND #3 CYLINDERS.

Are there any faults in #1 and #3 cylinders?

Repair or replace faulty parts.

NOTE:

Check the following items.

• Spark plug

• Fuel injector

• Skipping timing belt teeth

Go to DTC P0171.

25.GROUP OF #2 AND #4 CYLINDERS.

Are there any faults in #2 and #4 cylinders?

Repair or replace faulty parts.

NOTE:

Check the following items.

• Spark plug

• Fuel injector

• Compression ratio

• Skipping timing belt teeth

Go to DTC P0171.

26.CYLINDER AT RANDOM.

Is the engine idle rough?

Go to DTC P0171.

Repair or replace faulty parts.

NOTE:

Check the following items.

• Spark plug

• Fuel injector

• Compression ratio