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Home >> Subaru >> 2015 >> WRX Limited, Automatic CVT Trans >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 7 (Engine Controls (Diagnostics) (H4DOTC) (STI)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0304 Cylinder 4 Misfire Detected >> Wiring Diagram

DTC P0304 Cylinder 4 Misfire Detected: Wiring Diagram

WARNING: This page is about a different variant/trim than selected.
Fig 1: Cylinder 4 Misfire Detected - Wiring Diagram
G10265802Courtesy of SUBARU OF AMERICA, INC.
DIAGNOSTIC PROCEDURE

Step Check Yes No
1 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 (B134) No. 10 (+) - Chassis ground (-): 

    #2 (B134) No. 11 (+) - Chassis ground (-): 

    #3 (B134) No. 12 (+) - Chassis ground (-): 

    #4 (B134) No. 13 (+) - Chassis ground (-): 

 Is the voltage 10 V or more? Go to step 6  . Go to step 2  .
2 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from fuel injector on faulty cylinders.
  3. Measure the resistance between fuel injector connector 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 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 connector and fuel injector connector on faulty cylinders.
Connector & terminal 
#1 (B134) No. 10 - (E5) No. 2: 
#2 (B134) No. 11 - (E16) No. 2: 
#3 (B134) No. 12 - (E6) No. 2: 
#4 (B134) No. 13 - (E17) No. 2: 		 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 fuel injector terminals on faulty cylinder.
Terminals 
No. 1 - No. 2: 		 Is the resistance 5 - 20 Ω? Go to step 5  . Replace the faulty fuel injector. <Ref. to FUEL INJECTOR .>
5 CHECK POWER SUPPLY LINE. 
  1. Turn the ignition switch to ON.
  2. Measure the voltage between fuel injector connector of faulty cylinders 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 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 the main relay connector and fuel injector connector on faulty cylinders
  • Poor contact of coupling connector
  • Poor contact of main relay connector
6 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR 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 (B134) No. 10 (+) - Chassis ground (-): 

    #2 (B134) No. 11 (+) - Chassis ground (-): 

    #3 (B134) No. 12 (+) - Chassis ground (-): 

    #4 (B134) No. 13 (+) - 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. 
7 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 5 - 20 Ω? Go to step 8  . Replace the faulty fuel injector. <Ref. to FUEL INJECTOR .>
8 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. <Ref. to CAMSHAFT POSITION SENSOR .> <Ref. to CRANKSHAFT POSITION SENSOR .> 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 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 cylinder block.
ST 499987500 CRANKSHAFT SOCKET		 Is the timing belt dislocated from its proper position? Repair the installation condition of timing belt. <Ref. to 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 INDICATOR LIGHT. 
  1. Clear the memory using the Subaru Select Monitor or general scan tool. <Ref. to 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  .
13 CHECK CAUSE OF MISFIRE.  Was the cause of misfire identified when the engine is running? Finish diagnostics operation, if the engine has no abnormality. Repair the poor contact of connector.
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 of ECM connector
  • Poor contact of coupling connector
14 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 15. 
15 CHECK MISFIRE SYMPTOM. 
  1. Turn the ignition switch to ON.
  2. Check for DTC. <Ref. to READ DIAGNOSTIC TROUBLE CODE (DTC) .>
 Does the Subaru Select Monitor or general scan tool indicate only one DTC? Go to step 18  . Go to step 16  .
16 CHECK DTC.  Is DTC P0301 and P0303 displayed on the Subaru Select Monitor or general scan tool? Go to step 19  . Go to step 17  .
17 CHECK DTC.  Is DTC P0302 and P0304 displayed on the Subaru Select Monitor or general scan tool? Go to step 20  . Go to step 21  .
18 ONLY ONE CYLINDER.  Is there any fault in the cylinder? Repair or replace faulty parts.
NOTE: Check the following items.

  • Spark plug
  • Ignition coil
  • Fuel injector
  • Compression ratio
 Go to DTC P0171. <Ref. to DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC).>
19 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
  • Ignition coil
  • 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).>
20 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
  • Ignition coil
  • 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).>
21 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
  • Ignition coil
  • Fuel injector
  • Compression ratio
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