Has your vehicle recently set a p0304 fault code?
If so, don’t worry. You are in the right place.
In this PopularMechanic article you will learn:
- What Does The p0304 Code Mean?
- What Caused The p0304 code (Possible Symptoms)?
- How To Diagnose An p0304 Code?
And Much More!
No one wants to be greeted by a pesky check engine light when hopping in their vehicle, and striking out for their morning commute.
If the underlying cause of your check engine light is a p0304 trouble code, then your vehicle’s PCM has detected a malfunction that must be diagnosed.
Once diagnosed, the root cause of this issue can be addressed, and your check engine light can be cleared.
Luckily, a p0304 fault is seldom indicative of a severe issue, and will likely only require minor troubleshooting to properly repair.
What Does The p0304 Code Mean?
Fault code p0304 is the designated indicator for “cylinder 4 misfire detected.” This powertrain fault code is generic in nature and can be set on any make and model of vehicle with OBD-II capabilities.
Check out this article for more on engine misfire codes.
This is essentially a misfire code, that corresponds with the engine’s fourth cylinder. The presence of a cylinder specific misfire code can be quite helpful when attempting to obtain a diagnosis.
This is because the engine’s management software has already isolated the issue.
The PCM uses readings from the camshaft and crankshaft position sensors to determine engine speed, in correlation to individual coil voltages, to determine which cylinder is currently misfiring.
In order to repair your vehicle’s issue, you must identify the root cause of your engine’s cylinder misfire.
It is important to quickly diagnose and repair any issues that are contributing to a p0304 fault code.
An engine-misfire condition that goes unattended to, can lead to catalytic converter issues, due to the downrange passage of incorrect fuel mixtures.
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What Caused The p0304 code (Possible Symptoms)?
There are a number of possible causes for the presence of a p0304, misfiring cylinder error code. Some of the most common causes include:
- Faulty fuel injectors
- Low fuel pressure
- Failing coil packs
- Bad spark plugs
- Aging spark plug wires
- Damaged or worn distributor cap
- Faulty EGR valve operation
- Large vacuum leaks (such as those caused by an intake manifold gasket leak)
In rare cases, this code can be attributed to an internal engine issue that leads to compression loss on a specific cylinder. Such conditions include blown head gaskets and damaged/broken piston rings, or valve train issues.
Symptoms of a p0304 fault code include, but are not limited to:
- Poor or rough idling
- Fluctuations in fuel economy
- Constant or flashing engine light
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How To Diagnose An p0304 Code?
Your vehicle’s engine requires air, fuel, and properly timed spark in order to facilitate combustion on any given cylinder.
The absence of any of these three factors will lead to a misfire condition.
Additionally, each cylinder must be capable of containing adequate compression when called upon to do so upon the cylinder’s compression stroke.
Whenever a p0304 fault code is logged, you must determine which of these key factors are missing from the combustion process.
The following steps will assist you in making this determination.
- Check for Additional Codes
- Check all Wiring and Connectors
- Swap Cylinder Components
- Check for Proper Fuel Delivery
- Compression Testing
Step 1: Check for Additional Codes
Before beginning the diagnosis process, check for the presence of additional diagnostic trouble codes.
If any such codes exist, they should be rectified to prevent misdiagnosis, and to eliminate the presence of additional issues.
Step 2: Check all Wiring and Connectors
A visual inspection of all wiring and connectors related to fuel or ignition system function should be conducted.
This includes coil and plug wire connections, as well as those to all fuel injectors.
Step 3: Swap Cylinder Components
Step 3: If no visual issues can be identified, begin swapping cylinder number four ignition components to the next accessible cylinder.
Only swap one component at a time, and monitor OBD-II data to see if the location of the misfire changes in a similar fashion.
Begin by switching the affected cylinder’s coils. If the misfire condition does not switch cylinders, repeat this process with the corresponding spark plug wire and spark plug as well.
If the swapping of a particular component causes a shift in the affected cylinder, this component should be replaced.
Step 4: Check for Proper Fuel Delivery
With your engine’s ignition system checked, it will now be time to check for proper fuel delivery.
This can be done by attaching a mechanical gauge to the schrader port on your engine’s fuel rail.
Compare the observed reading to manufacturer specifications.
If low fuel pressure is found to be present, a faulty fuel pump, failed fuel pressure regulator, or clogged fuel filter is suspect.
Fuel injector functionality should also be verified per the manufacturer’s guidelines.
Step 5: Compression Testing
If the source of your engine’s malfunction has not yet been located, further mechanical testing will be necessary. The completion of a compression test, as well as a leakdown test are highly advised.
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How Do I Fix An p0304 Code?
- Fix any Additional Codes
- Replace Malfunctioning Ignition System Components
- Replace any Needed Fuel System Components
- Seek Repair for Low Compression
- Test Drive Vehicle
Step 1: Fix Any Additional Codes
Remedy any additional codes that are present outside of fault code p0304. In the process, it is possible that the root cause of DTC p0304 will be uncovered.
Step 2: Replace Malfunctioning Ignition System Components
Replace any malfunctioning ignition system components that have been identified during your initial diagnosis.
Step 3: Replace Any Needed Fuel System Components
Replace any fuel system components that are contributing to insufficient fuel pressure. Additionally, replace any fuel filters that are found to be faulty.
Step 4: Seek Repair For Low Compression
If low compression is determined to be at the root of your misfire issue, internal mechanical repair of the engine will be inevitable.
Step 5: Test Drive Vehicle
Thoroughly test drive your vehicle upon the completion of any repair. This ensures that all symptoms have been alleviated, and your check engine light will remain off.
Though a number of potential problems can set a p0304 fault code, most are relatively simple to fix and lead to only a minimal expenditure in parts.
If you have any doubt as to how any faulty component is replaced, consult manufacturer's backed, factory service literature.
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Eliminating Troublesome p0304 Fault Codes
Though no one wants to be faced with the annoyance of an irritating check engine light, and imminent repairs, by following the process outlined above, your vehicle will be operating like its old reliable self in no time.
What might at first seem worrisome, is seldom as difficult to remedy as one might think.
If you take your time to achieve an accurate diagnosis and are thorough and concise in your repairs, your vehicle’s p0304 fault code will quickly become a thing of the past.