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HOMESERVICE MANUALSSUBARU2005OUTBACK I, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - ENGINE (DIAGNOSTICS) (H4SO)DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)DTC P0304 CYLINDER 4 MISFIRE DETECTED
2005 Subaru Outback i, Standard

DTC P0304 Cylinder 4 Misfire Detected

2005 Subaru Outback i, StandardSECTION DTC P0304 Cylinder 4 Misfire Detected

DTC DETECTING CONDITION: 

  • Two consecutive driving cycles with fault
  • Detect as soon as malfunction occurs. (A misfire which could damage catalyst occurs.)
  • GENERAL DESCRIPTION < Ref. to DTC P0304 CYLINDER 4 MISFIRE DETECTED , Diagnostic Trouble Code (DTC) Detecting Criteria. >

TROUBLE SYMPTOM: 

  • Engine stalls.
  • Erroneous idling
  • Rough driving
CAUTION: After repair or replacement of faulty parts, conduct Clear Memory Mode < Ref. to , OPERATION , Clear Memory Mode.> and Inspection Mode < Ref. to , PROCEDURE , Inspection Mode.>.

WIRING DIAGRAM: 

Fig 1: DTC P0304 Circuit
G03828474Courtesy of SUBARU OF AMERICA, INC.
DTC P0304 DIAGNOSIS

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 , LIST OF DIAGNOSTIC TROUBLE CODE (DTC) . >
NOTE: In this case, it is not necessary to inspect DTC P0301, P0302, P0303 and P0304.
 Go to step 2. 
2. CHECK OUTPUT SIGNAL FROM ECM. 
  1. Turn the ignition switch to ON.
  2. Measure the voltage between ECM connector and chassis ground on faulty cylinders.

    Connector & terminal 

    #1 (B136) No. 6 (+) - Chassis ground (-): 

    #2 (B136) No. 5 (+) - Chassis ground (-): 

    #3 (B136) No. 4 (+) - Chassis ground (-): 

    #4 (B136) No. 3 (+) - Chassis ground (-): 

 Is the voltage more than 10 V? Go to step 7.  Go to step 3. 
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. 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 more than 1 MΩ? Go to step 4.  Repair ground short circuit in 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 (B136) No. 6 - (E5) No. 1: 

#2 (B136) No. 5 - (E16) No. 1: 

#3 (B136) No. 4 - (E6) No. 1: 

#4 (B136) No. 3 - (E17) No. 1: 

 Is the resistance less than 1 Ω? Go to step 5.  Repair harness and connector.
NOTE: In this case, repair the following:
  • Open circuit in harness between ECM and fuel injector connector
  • Poor contact in coupling connector
5. 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 6.  Replace the faulty fuel injector.< Ref. to 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 more than 10 V? Repair poor contact in all connectors in fuel injector circuit. Repair harness and connector.
NOTE: In this case, repair the following:
  • Open circuit in harness between main relay and fuel injector connector on faulty cylinders
  • Poor contact in coupling connector
  • Poor contact in main relay connector
  • Poor contact in 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 cylinder.
  3. Turn the ignition switch to ON.
  4. Measure the voltage between ECM connector and chassis ground on faulty cylinders.

    Connector & terminal 

    #1 (B136) No. 6 (+) - Chassis ground (-): 

    #2 (B136) No. 5 (+) - Chassis ground (-): 

    #3 (B136) No. 4 (+) - Chassis ground (-): 

    #4 (B136) No. 3 (+) - Chassis ground (-): 

 Is the voltage more than 10 V? Repair battery short circuit in harness between ECM and fuel injector. After repair, replace the ECM. < Ref. to ENGINE CONTROL MODULE (ECM) . > Go to step 8. 
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< Ref. to FUEL INJECTOR .> and ECM < Ref. to ENGINE CONTROL MODULE (ECM) > Go to step 9. 
9. CHECK INSTALLATION OF CAMSHAFT POSITION SENSOR/CRANKSHAFT POSITION SENSOR.  Is the camshaft position sensor or crankshaft position sensor loosely installed? Tighten camshaft position sensor or crankshaft position sensor. Go to step 10. 
10. 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 CRANK SPROCKET . > Go to step 11. 
11. CHECK INSTALLATION CONDITION OF TIMING BELT. 

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

 Is the timing belt dislocated from its proper position? Repair installation condition of timing belt. < Ref. to TIMING BELT . > Go to step 12. 
12. CHECK FUEL LEVEL.  Is the fuel meter indication higher than the "Lower" level? Go to step 13.  Replenish fuel so fuel meter indication is higher than the "Lower" level. After replenishing fuel, Go to step 13. 
13. CHECK STATUS OF MALFUNCTION INDICATOR LIGHT. 
  1. Clear the memory using Subaru Select Monitor.

    < Ref. to , CLEAR MEMORY MODE . >

  2. Start the engine, and drive the vehicle more than 10 minutes.
 Does the malfunction indicator light illuminate or blink? Go to step 16.  Go to step 14. 
14. CHECK CAUSE OF MISFIRE DIAGNOSED.  Was the cause of misfire identified when the engine is running? Ex. Disconnection of spark plug cord. Finish diagnostics operation, if the engine has no abnormality. Go to step 15. 
15. CHECK FOR POOR CONTACT.  Is there poor contact in the ignition coil, fuel injector, ECM and coupling connector? Repair poor contact. Contact your SOA Service Center after checking followings.
NOTE: In this case, check the following:
  • Condition of fuel
  • Fuel additive used or not
  • Visually check spark plug
  • Visually check spark plug cord
  • Condition of engine oil
16. CHECK AIR INTAKE SYSTEM.  Is there any fault in air intake system? Repair 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? Go to step 17. 
17. CHECK MISFIRE SYMPTOM. 
  1. Turn the ignition switch to ON.
  2. Read the DTC.
NOTE:
  • Subaru Select Monitor

    For detailed operation procedures, refer to "READ CURRENT DATA FOR ENGINE". < Ref. to , SUBARU SELECT MONITOR . >

    • OBD-II general scan tool

      For detailed operation procedures, refer to the OBD-II general scan tool operation manual.

    NOTE: Perform diagnosis according to the items listed below.
 Does the Subaru Select Monitor or OBD-II general scan tool display only one DTC? Go to step 22.  Go to step 18. 
18. CHECK DTC ON DISPLAY  .

Is any other DTC displayed?

 Does the Subaru Select Monitor or OBD-II general scan tool indicate DTC P0301 and P0302? Go to step 23.  Go to step 19. 
19. CHECK DTC ON DISPLAY. 
Is any other DTC displayed?		 Does the Subaru Select Monitor or OBD-II general scan tool indicate DTC P0303 and P0304? Go to step 24.  Go to step 20. 
20. CHECK DTC ON DISPLAY  .

Is any other DTC displayed?

 Does the Subaru Select Monitor or OBD-II general scan tool indicate DTC P0301 and P0303? Go to step 25.  Go to step 21. 
21. CHECK DTC ON DISPLAY. 

Is any other DTC displayed?

 Does the Subaru Select Monitor or OBD-II general scan tool indicate DTC P0302 and P0304? Go to step 26.  Go to step 27. 
22. ONLY ONE CYLINDER  Is there any fault in that cylinder? Repair or replace faulty parts.
NOTE: Check the following items.
  • Spark plug
  • Spark plug cord
  • Fuel injector
  • Compression ratio
 Go to DTC P0171.
< Ref. to , DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC). >
23. GROUP OF #1 AND #2 CYLINDERS  Are there faults in #1 and #2 cylinders? Repair or replace faulty parts.
NOTE: Check the following items.
  • Spark plugs
  • Fuel injectors
  • Ignition coil
  • Compression ratio
  • If no abnormal is discovered, check for "IGNITION CONTROL SYSTEM" of #1 and #2 cylinders side.

< Ref. to , IGNITION CONTROL SYSTEM , Diagnostics for Engine Starting Failure. >		 Go to DTC P0171.
< Ref. to , DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC). >
24. GROUP OF #3 AND #4 CYLINDERS  Are there faults in #3 and #4 cylinders? Repair or replace faulty parts.
NOTE:
  • Check the following items.
  • Spark plugs
  • Fuel injectors
  • Ignition coil
  • If no abnormal is discovered, check for "IGNITION CONTROL SYSTEM" of #3 and #4 cylinders side.

< Ref. to , IGNITION CONTROL SYSTEM , Diagnostics for Engine Starting Failures		 Go to DTC P0171.
< Ref. to , DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC). >
25. GROUP OF #1 AND #3 CYLINDERS  Are there faults in #1 and #3 cylinders? Repair or replace faulty parts.
NOTE: Check the following items.
  • Spark plugs
  • Fuel injectors
  • Skipping timing belt teeth
 Go to DTC P0171.
< Ref. to , DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC). >
26. GROUP OF #2 AND #4 CYLINDERS  Are there faults in #2 and #4 cylinders? Repair or replace faulty parts.
NOTE: Check the following items.
  • Spark plugs
  • Fuel injectors
  • Compression ratio
  • Skipping timing belt teeth
 Go to DTC P0171. < Ref. to , DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC). >
27. CYLINDER AT RANDOM  Is the engine idle rough? Go to DTC P0171. < Ref. to , DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC). > Repair or replace faulty parts.
NOTE: Check the following items.
  • Spark plugs
  • Fuel injectors
  • Compression ratio
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.