P0304 Subaru Code - Cylinder 4 Misfire Detected
Quick Answer
When a Subaru vehicle shows a P0304 diagnostic trouble code (DTC), it means that a misfire has been detected in cylinder 4 of the engine. Common causes include Faulty spark plug in cylinder 4, Malfunctioning ignition coil in cylinder 4, Clogged or dirty fuel injector in cylinder 4. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P0304 Subaru indicates Cylinder 4 Misfire Detected.
- Common causes
- Common causes include Faulty spark plug in cylinder 4, Malfunctioning ignition coil in cylinder 4, Clogged or dirty fuel injector in cylinder 4.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
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Code P0304 Subaru Description
When a Subaru vehicle shows a P0304 diagnostic trouble code (DTC), it means that a misfire has been detected in cylinder 4 of the engine. This misfire can be caused by a variety of issues, including problems with the ignition system, fuel system, or engine mechanical components.
Common Causes of P0304 Subaru
- Faulty spark plug in cylinder 4
- Malfunctioning ignition coil in cylinder 4
- Clogged or dirty fuel injector in cylinder 4
- Vacuum leak affecting cylinder 4
- Low compression in cylinder 4 due to worn piston rings or valves
Symptoms of P0304 Subaru
- Rough idle or shaking sensation while the engine is running
- Loss of power or acceleration
- Engine misfiring or hesitation during acceleration
- Increased fuel consumption
- Check Engine Light illuminated on the dashboard
How to Fix P0304 Subaru
- Perform a thorough inspection of the ignition system, including spark plugs, ignition coils, and spark plug wires, and replace any faulty components.
- Check the fuel injectors for clogs or leaks, and clean or replace as necessary.
- Conduct a compression test to check the health of the engine cylinders, focusing on cylinder 4, and address any low compression issues.
- Inspect the intake manifold and vacuum lines for leaks, and repair or replace any damaged components.
- Clear the diagnostic trouble code from the vehicle's computer system after completing the repairs, and test drive the vehicle to ensure the issue has been resolved.
Cost to Fix P0304 Subaru
The cost of repairing a cylinder 4 misfire in a Subaru can vary depending on the specific cause of the issue and the labor rates in your area. Typically, replacing spark plugs, ignition coils, or fuel injectors can range from $100 to $300 per component, including parts and labor. Additional diagnostic tests or repairs may increase the total cost. It is recommended to consult with a professional mechanic for a more accurate estimate based on your vehicle's make and model.
Tech Notes for P0304 Subaru
When is the Code Detected?
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Frequently Asked Questions about P0304 Subaru Code
1. What are common symptoms of OBDII code P0304 in a Subaru indicating Cylinder 4 Misfire Detected?
- Common symptoms include engine hesitation, rough idling, loss of power, and potential increased fuel consumption.
2. What are the possible causes of a Cylinder 4 misfire in a Subaru triggering code P0304?
- Causes may include faulty spark plugs, ignition coils, fuel injectors, vacuum leaks, low compression, or an issue with the engine control module.
3. How can I diagnose the source of the Cylinder 4 misfire in my Subaru with code P0304?
- Diagnostic steps may involve checking spark plugs, inspecting ignition coils, testing fuel injectors, performing a compression test, and scanning for other trouble codes.
4. Can driving with OBDII code P0304 in a Subaru be harmful to the engine?
- Continuing to drive with a misfire can potentially cause damage to the catalytic converter and other engine components, leading to more costly repairs.
5. What are some basic repair tips for addressing code P0304 in a Subaru related to Cylinder 4 misfire?
- Start with checking and replacing spark plugs, inspecting ignition coils, verifying fuel injector operation, and ensuring there are no vacuum leaks.
6. If I clear the OBDII code P0304 in my Subaru, how long should I drive to see if the issue returns?
- It is recommended to drive the vehicle for a few days under different conditions to allow the system to monitor and detect any potential misfires before assuming the problem is resolved.
7. Can a dirty air filter cause OBDII code P0304 in a Subaru indicating Cylinder 4 misfire?
- While a dirty air filter can impact engine performance, it is less likely to directly cause a specific cylinder misfire. Focus on checking ignition and fuel components first.
8. Is it safe to continue driving my Subaru with code P0304 if the engine is running smoothly despite the error code?
- Even if the engine appears to run smoothly, it is advisable to address the misfire promptly to prevent any potential long-term damage to the engine or emissions system.
9. Will a Cylinder 4 misfire in a Subaru with code P0304 affect the vehicle's emissions and cause it to fail an emissions test?
- Yes, a misfire can lead to increased emissions, potentially causing the vehicle to fail an emissions test. Resolving the misfire is crucial for passing emissions inspections.
10. How much can I expect to pay for repairs related to OBDII code P0304 in a Subaru with a Cylinder 4 misfire?
- The cost of repairs can vary depending on the root cause of the misfire and labor rates, but it is advisable to budget for potential expenses related to replacing spark plugs, ignition coils, or other components.
Discuss the causes and fixes for P0304 Subaru OBDII Code
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With a misfire always check if you spark plugs are tight I was working on a 06 Subaru Outback 2.5 Turbo and number 4 cylinder misfiring. LoL they took it to dealership and charged $1200 to change some vacuum lines the car still had same problem then he took it to midas they could not figure it out. When I took the plug was diagnosing it checked the simple things one of them being the plugs in the plug on number 4 was hand tight I was lost for words. Any way always check the simple things first
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i have a 2015 subaru forester dit. 2.0 boxer engine it is throwing codes p0300 p0304 misfires cylinder 4 multiple misfire can someone help me???
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Unfortunately there are many things that could trigger the P0300 and P0304 code. There is a factory service bulletin that recommends reprogramming the Engine Control Module (ECM). You could either start by reprogramming the ECM or replacing the spark plugs.
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Got this code on my 2005 Forester and left it at my usual repair shop last evening for a check up this morning.
They tell me it's the usual "Subaru Issue" that is, it needs a head gasket, oil is spewing out, plug 4 is sitting in oil, needs new plugs, valve cover gasket, tube seals, ignition wires...
So what do you guys think?? I have no oil drips, no drips or puddles of any kind. No noticeable oil on engine. Had spoken by phone with a mechanic Saturday and he felt I needed a coil pack. Just talked with him now to tell him the current prognosis and he still feels a coil pack is the best place to start. Again, WHAT DO YOU GUYS THINK???
THANKS -
Sometimes the valve cover gasket leaks inside and you may not notice oil on the engine.
The spark plugs and wires are common than ignition coils, and if you haven't replace the spark plugs lately, in my opinion is the best place to start.
I checked a national database of repairs for the P0304 code on you model year, and out 402 repairs reported, 181 was the spark plugs, 158 the spark plugs wires and 63 the ignition coil. -
Needs spark plugs and new wires, coil pack and valve cover gasket. Sounds right to me, based on all my research and input from folks who know cars. $995. vs $2500. Thanks again.
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Can you hold the spark plug against something to check for spark like a lawnmower? I replaced the plugs and wires and still have a miss on four. Can the coil go bad on just one cylinder and not the others since it has just one coil?
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You can hold the tip of the spark plug against any metal part that is grounded.
Yes, one coil can go bad and the other can be OK.
What model and year is your vehicle? -
2006 Forrester 2.5L automatic. I held the spark plug against metal and no spark on cylinder 4.
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Do the other plugs have spark? if you do, then the problem is more than likely the ignition coil. Also make sure the wires are not cracks or damage.
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Thank you, Yes the other cylinders have spark. I put new plugs and wires on and checked two plugs on the one with no spark to make sure it wasn't the plugs or wires. Just wasn't sure if the coil would go bad for one and not the others since it is one coil for all four cylinders. Thanks again.
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