DTC P0304: Cylinder 4 Misfire Detected: Notes

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>ENGINE ELECTRICAL SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>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)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR .
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 and 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.
CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR .
Measure the resistance of harness between ECM and fuel injector connector on faulty cylinders.

Connector and 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.
CHECK FUEL INJECTOR .
Check the fuel injector on faulty cylinder. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>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)>FUEL INJECTOR .
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)>CAMSHAFT POSITION SENSOR>INSTALLATION . Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>CRANKSHAFT POSITION SENSOR>INSTALLATION .

No : Go to 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 FUEL INJECTION (FUEL SYSTEMS) (H4DO)>CRANKSHAFT POSITION SENSOR PLATE .

No : Go to 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)>TIMING CHAIN ASSEMBLY .

No : Go to 7 .
CHECK PCV VALVE .
Check the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV VALVE>INSPECTION .

Is the check result OK?

Yes : Go to 8 .

No : Repair or replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV VALVE .
CHECK PCV HOSE .
Check the PCV hose. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV HOSE>INSPECTION .

Is the check result OK?

Yes : Go to 9 .

No : Repair or replace the PCV hose. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV HOSE .
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. Start the engine, and drive the vehicle at 60 km/h (37.3 MPH) or more for 10 minutes or more.
  WARNING: Use special care with the traffic condition on the public road and prioritize safety driving.
  
  NOTE: Refill the fuel before driving so that the fuel level meter indicates above "Lower" level.
Does the malfunction indicator light illuminate or blink?

Yes : Go to 10 .

No : 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
CHECK AIR INTAKE SYSTEM .
Check the installing condition of the air intake system.

Are there holes, loose bolts or disconnection of hose on air intake system?

Yes : Repair the air intake system. Ref. to INTAKE (INDUCTION) (H4DO)>GENERAL DESCRIPTION .

No : Go to 11 .
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.

No : Go to DTC PO171. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)>DTC P0171: SYSTEM TOO LEAN BANK 1 .