Safety Warning

DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.

2014 Subaru Forester 2.5i, Eng CD FB25BA, Standard TransFACTORY OEM SERVICE PROCEDURE

DTC P0304: Cylinder 4 Misfire Detected: Wiring Diagram

Engine electrical system non-turbo model (without push button start) < Ref. to NON-TURBO MODEL (WITHOUT PUSH BUTTON START) , WIRING DIAGRAM, Engine Electrical System. >
Engine electrical system non-turbo model (with push button start) < Ref. to NON-TURBO MODEL (WITH PUSH BUTTON START) , WIRING DIAGRAM, Engine Electrical System. >

Fig 1: Cylinder - Wiring Diagram
Courtesy of SUBARU OF AMERICA, INC.

DTC PROCEDURE

Step	Check	Yes	No
1 CHECK OUTPUT SIGNAL OF ECM . Turn the ignition switch to ON. Measure the voltage between ECM and chassis ground on faulty cylinders. Connector & terminal #1 (B134) No. 12 (+) - Chassis ground (-): #2 (B134) No. 22 (+) - Chassis ground (-): #3 (B134) No. 32 (+) - 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 . Turn the ignition switch to OFF. Disconnect the connector from fuel injector on faulty cylinders. Measure the resistance between fuel injector 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 1 MΩ or more?	Go to step 3 .	Repair the short circuit to ground in harness between ECM and fuel injector connector.
3 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR . Measure the resistance of harness between ECM and fuel injector connector on faulty cylinders. Connector & terminal #1 (B134) No. 12 - (E5) No. 1: #2 (B134) No. 22 - (E16) No. 1: #3 (B134) No. 32 - (E6) No. 1: #4 (B134) No. 13 - (E17) No. 1:	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 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 . Turn the ignition switch to ON. 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 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 . Turn the ignition switch to OFF. Disconnect the connector from fuel injector on faulty cylinders. Turn the ignition switch to ON. Measure the voltage between ECM and chassis ground on faulty cylinders. Connector & terminal #1 (B134) No. 12 (+) - Chassis ground (-): #2 (B134) No. 22 (+) - Chassis ground (-): #3 (B134) No. 32 (+) - 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 and fuel injector connector.	Go to step 7 .
7 CHECK FUEL INJECTOR . Turn the ignition switch to OFF. 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 CONDITION 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 INSTALLATION , Camshaft Position Sensor. > < Ref. to INSTALLATION , Crankshaft Position Sensor. >	Go to step 9 .
9 CHECK CRANKSHAFT POSITION SENSOR PLATE .	Is the crankshaft position sensor plate rusted or does it have broken teeth?	Replace the crankshaft position sensor plate. < Ref. to CYLINDER BLOCK . >	Go to step 10 .
10 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?	Correct the installation condition of timing chain. < Ref. to TIMING CHAIN ASSEMBLY . >	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 . Clear the memory using the Subaru Select Monitor. < Ref. to CLEAR MEMORY MODE . > 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 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 Skipping timing chain teeth	Go to DTC P0171. < Ref. to DTC P0171 SYSTEM TOO LEAN (BANK 1) , Diagnostic Procedure with Diagnostic Trouble Code (DTC). >

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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.

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