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DTC P0304: Cylinder 4 Misfire Detected: Notes

WARNING: This page is about a different variant/trim than selected.
  1. - 

    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 stall
    • Improper idling
    • Rough driving

    Wiring diagram: 

    Engine Electrical System Ref. to WIRING SYSTEM (CROSSTREK MODEL (HEV))>ENGINE ELECTRICAL SYSTEM .

G13237389Courtesy of SUBARU OF AMERICA, INC.
CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO (HEV))>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .
NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO (HEV))>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .
G13615264Courtesy of SUBARU OF AMERICA, INC.
G13615265Courtesy of SUBARU OF AMERICA, INC.
  1. CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR  .
    1. Turn the ignition switch to OFF.
    2. Disconnect the connector from ECM.
    3. Disconnect the connector from fuel injector on faulty cylinders.
    4. Measure the resistance between fuel injector connector and engine ground on faulty cylinders.

      Connector & terminal 

      #1 (E5) No. 1 - Engine ground:

      #1 (E5) No. 2 - Engine ground:

      #2 (E16) No. 1 - Engine ground:

      #2 (E16) No. 2 - Engine ground:

      #3 (E6) No. 1 - Engine ground:

      #3 (E6) No. 2 - Engine ground:

      #4 (E17) No. 1 - Engine ground:

      #4 (E17) No. 2 - Engine ground:

      Is the resistance 1 MΩ or more?

      Yes:  Go to  2.

      No:  Repair the short circuit to ground in harness between ECM and fuel injector connector.

  2. CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR  .

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

    Connector & terminal 

    #1 (E158) No. 96 - (E5) No. 1:

    #1 (E158) No. 87 - (E5) No. 2:

    #2 (E158) No. 95 - (E16) No. 1:

    #2 (E158) No. 86 - (E16) No. 2:

    #3 (E158) No. 93 - (E6) No. 1:

    #3 (E158) No. 84 - (E6) No. 2:

    #4 (E158) No. 94 - (E17) No. 1:

    #4 (E158) No. 85 - (E17) No. 2:

    Is the resistance less than 1 Ω?

    Yes:  Go to  3.

    No:  Repair the open circuit in harness between ECM and fuel injector connector.

  3. CHECK FUEL INJECTOR  .

    Check the fuel injector on faulty cylinder. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (HEV))>FUEL INJECTOR>INSPECTION .

    Is the check result OK?

    Yes:  Go to  4.

    No:  Replace the faulty fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (HEV))>FUEL INJECTOR .

  4. CHECK INSTALLATION CONDITION OF CAMSHAFT POSITION SENSOR AND CRANKSHAFT POSITION SENSOR  .

    Check the installation condition of the camshaft position sensor and crankshaft position sensor.

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

    Yes:  Install the camshaft position sensor or crankshaft position sensor properly. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (HEV))>CAMSHAFT POSITION SENSOR>INSTALLATION . Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (HEV))>CRANKSHAFT POSITION SENSOR>INSTALLATION .

    No:  Go to  5.

  5. CHECK CRANKSHAFT POSITION SENSOR PLATE  .

    Check the crankshaft position sensor plate.

    Is the crankshaft position sensor plate rusted or does it have broken teeth?

    Yes:  Replace the crankshaft position sensor plate. Ref. to MECHANICAL (H4DO (EXCEPT FOR HEV))>CYLINDER BLOCK .

    No:  Go to  6.

  6. CHECK INSTALLATION CONDITION OF TIMING CHAIN  .

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

    ST 18252AA000 CRANKSHAFT SOCKET 

    Is the timing chain dislocated from its proper position?

    Yes:  Correct the installation condition of timing chain. Ref. to MECHANICAL (H4DO (EXCEPT FOR HEV))>TIMING CHAIN ASSEMBLY .

    No:  Go to  7.

  7. CHECK PCV VALVE  .

    Check the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO (HEV))>PCV VALVE>INSPECTION .

    Is the check result OK?

    Yes:  Go to  8.

    No:  Replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO (HEV))>PCV VALVE .

  8. CHECK PCV HOSE  .

    Check the PCV hose. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO (HEV))>PCV HOSE>INSPECTION .

    Is the check result OK?

    Yes:  Go to  9.

    No:  Replace the PCV hose. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO (HEV))>PCV HOSE .

  9. CHECK FUEL LEVEL  .

    Check the fuel gauge display.

    Is the fuel meter indication higher than the "Lower" level?

    Yes:  Go to  10.

    No:  Refill the fuel so that the fuel meter indication is higher than the "Lower" level, and proceed to the next step. Go to  10.

  10. CHECK STATUS OF MALFUNCTION INDICATOR LIGHT  .
    1. Using the Subaru Select Monitor or a general scan tool, perform the clear memory of [Engine]. Ref. to COMMON (DIAG)>CLEAR MEMORY .
    2. Turn to READY ON.
    3. Press the hybrid mode switch to switch to the hybrid battery save mode.
      NOTE: Even if switched to the hybrid battery save mode under the following conditions, the engine may not start.
      • Power from HV battery is low and reduction in SOC is slight.
      • SOC is recovering due to regeneration, etc.
    4. Drive the vehicle at 60 km/h (37.3 MPH) or more for 10 minutes or more.

      Does the malfunction indicator light illuminate or blink?

      Yes:  Go to  11.

      No:  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

      Go to  11.

  11. CHECK AIR INTAKE SYSTEM  .

    Check the installing condition of the air intake system.

    Is there any fault in air intake system?

    Yes:  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?

    No:  Go to  12.

  12. CHECK CYLINDER  .

    Check the following items for cylinder.

    • Spark plug
    • Ignition coil
    • Fuel injector
    • Compression pressure
    • Skipping timing chain teeth

    Is there any fault in the cylinder?

    Yes:  Repair or replace faulty parts.

    NOTE: Check the following items.
    • Spark plug
    • Ignition coil
    • Fuel injector
    • Compression pressure
    • Skipping timing chain teeth

    No:  Go to DTC P0171. Ref. to ENGINE (DIAGNOSTICS) (H4DO (HEV))>DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)>DTC P0171 SYSTEM TOO LEAN BANK 1 .

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