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Home >> Subaru >> 2006 >> Legacy GT spec.B >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 11 (Engine Controls - Engine (Diagnostics) (H4SO)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0304 Cylinder 4 Misfire Detected

DTC P0304 Cylinder 4 Misfire Detected

WARNING: This page is about a different variant/trim than selected.

DTC DETECTING CONDITION: 

TROUBLE SYMPTOM: 

CAUTION: After repairing or replacing the defective part, perform the Clear Memory Mode < Ref. to OPERATION , Clear Memory Mode. > and Inspection Mode < Ref. to PROCEDURE , Inspection Mode. >.

WIRING DIAGRAM: 

Fig 1: Cylinder 4 Misfire Detected - Wiring Diagram
G05017576
DIAGNOSIS PROCEDURE

Step Check Yes No
1 CHECK 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 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 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 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? Go to step 5.  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 and 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 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 more than 10 V? Repair the battery short circuit of 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 the 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 damaged teeth? Replace the crank sprocket. < Ref. to CRANK SPROCKET . > Go to step 11  .
11 CHECK INSTALLATION CONDITION OF TIMING BELT. 
Turn the crankshaft, and align alignment mark on crank sprocket with alignment mark on cylinder block.		 Is the timing belt dislocated from its proper position? Repair the 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  . Refill the fuel so that fuel meter indication is higher than the "Lower" level. After filling 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.  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. Go to step 15  .
15 CHECK POOR CONTACT.  Is there poor contact in the ignition coil, fuel injector, ECM and coupling connector? Repair the 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 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?
 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 procedure, refer to "READ CURRENT DATA FOR ENGINE". < Ref. to SUBARU SELECT MONITOR . >

  • General scan tool

    For detailed operation procedure, refer to the general scan tool operation manual.

  • Perform the diagnosis according to following items.
 Does the Subaru Select Monitor or general scan tool display only one DTC? Go to step 22  . Go to step 18  .
18 CHECK DTC.  Are DTCs P0301 and P0302 displayed on the Subaru Select Monitor or general scan tool? Go to step 23  . Go to step 19  .
19 CHECK DTC.  Are DTCs P0303 and P0304 displayed on the Subaru Select Monitor or general scan tool? Go to step 24  . Go to step 20  .
20 CHECK DTC.  Are DTCs P0301 and P0303 displayed on the Subaru Select Monitor or general scan tool? Go to step 25  . Go to step 21  .
21 CHECK DTC.  Are DTCs P0302 and P0304 displayed on the Subaru Select Monitor or general scan tool? Go to step 26  . Go to step 27  .
22 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. < 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 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. < 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 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. < 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). >
25 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. < 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 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. < 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 plug
  • Fuel injector
  • Compression ratio
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