Cylinder 4 Misfire Detection: P0304 Error Code

DTCs (diagnostic trouble codes) come in use to identify engine-related issues in vehicles. A misfire is when a given cylinder does not experience an entire combustion event as anticipated. “Cylinder 4 Misfire Detected” is what the diagnostic trouble code (DTC) P0304 stands for. Several things can cause this. Thus, a technician must identify the precise cause in your case to clear the code. However, it might cause the internal engine to fail as a result. It is a serious issue nowadays. Thus, this code indicates a critical engine problem that needs quick treatment. Therefore, car owners need to comprehend these engine codes.

What is P0304 Error Code?

The code P0304 indicates a misfire in cylinder 4 of a gasoline-powered engine. The “P” stands for Powertrain, which includes the engine and transmission. The “0304” refers to the specific cylinder that is misfiring.

When the engine control module (ECM) detects a misfire, it will store a Diagnostic Trouble Code (DTC) and turn on the check engine light. A misfire occurs when a cylinder’s air/fuel mixture fails to ignite properly. Various factors, including faulty spark plugs, ignition coils, fuel injectors, vacuum leaks, or engine mechanical problems, can cause this.

What are the Causes of the P0304 Code?

A misfire in the fourth cylinder of a gasoline-powered engine typically causes the P0304 code. The misfire happens because of a variety of factors, including:

Faulty Spark Plug:

A damaged, fouled, or worn-out spark plug can prevent the air/fuel mixture from igniting correctly, leading to a misfire in cylinder 4.

Ignition Coil Failure:

The ignition coil creates the electrical charge that ignites the air/fuel mixture. However, if the coil for cylinder 4 is faulty, it can cause a misfire.

Fuel Injector Issues:

A clogged or malfunctioning fuel injector can prevent the proper amount of fuel from reaching cylinder 4, causing a misfire.

Vacuum Leaks:

Leaks in the engine’s vacuum system can cause a lean air/fuel mixture, resulting in a misfire.

Low Compression:

Low compression in cylinder 4 can cause a misfire, which worn piston rings, valves, or a damaged head gasket may cause.

Wiring Issues:

Faulty wiring or connections between the engine control module and the ignition coil or fuel injector for cylinder 4 can cause a misfire.

If you have a P0304 code, it is essential to have the problem diagnosed and repaired promptly to prevent further engine damage and improve performance and fuel efficiency.

What are the Signs of Code P0304?

Here are some common symptoms associated with this code:

Check Engine Light:

The most common symptom of code P0304 is the illumination of the check engine light on the dashboard.

Rough Idling:

A misfire in cylinder 4 can cause the engine to idle roughly, and you may notice that the engine shakes or vibrates more than usual.

Reduced Power and Acceleration:

The misfire can cause a decrease in engine power and acceleration, making it harder to reach high speeds.

Engine Vibration:

The misfire in cylinder 4 can cause the engine to vibrate more than usual, especially when idling or under load.

Poor Fuel Economy:

A misfire can cause the engine to burn more fuel than usual, reducing fuel economy.


In severe cases, the misfire can cause the engine to stall, which can be dangerous if it happens while driving.

How to Resolve P0304 Error Code?

The fixing process includes the following steps:

Monitor more DTCs

Before beginning the diagnostic procedure, it is crucial to ascertain whether more DTCs have been stored. If this happens to be the case, you must rapidly diagnose and fix other codes.

Doing a Freeze-Frame Data Analysis

Any freeze-frame data acquired from the DTC logging can also be examined. This information may offer additional details that are helpful during the diagnosing process. You can mark out the RPM range when these misfires happen.

Thoroughly Inspect the Ignition System’s Parts

Misfires happen when one or more ignition system components in an engine malfunction. You must therefore be sure to check such parts for damage or failure carefully.

Look for Any Signs of a Spark

As indicated previously, you must verify the presence of a spark on the defective cylinder. If you find no apparent flaws during the inspection, you may use an inline spark tester for this.

Verify the fuel System’s Integrity and Functionality

You must install a fuel pressure gauge in the engine’s fuel rail. The “Key On” fuel pressure readings must be within the manufacturer’s standards or meet the P0304.

Test the Compression of the Air

To check the cylinder for damage, perform a compression test. If your car has no fuel issues, you should still do this. Compare the outcomes after that.

Verify the Factory Service Data

Before beginning any extensive deconstruction, checking factory-specific servicing information for your particular car is vital. Potential problems will be highlighted by this information, together with torque values for completing the task.

Cylinder 4 Misfire Detection

How Much Does It Cost to Fix the P0304 Code?

The cost to fix the P0304 code can vary depending on the cause of the problem and where you take your vehicle to be repaired.

The P0304 code typically indicates a misfire in cylinder 4, which a variety of issues, such as a faulty spark plug or ignition coil, a vacuum leak, or a problem with the fuel injector, can cause.

If the issue is a faulty spark plug or ignition coil, the cost to replace these parts can range from $100 to $300, depending on the make and model of your vehicle and where you have the work done.

If the issue is a vacuum leak or a problem with the fuel injector, the cost to repair can be more expensive, ranging from $300 to $1,000 or more, depending on the severity of the issue and the type of vehicle you have.

It’s always best to consult with a trusted mechanic or dealership to get a proper diagnosis and estimate the cost of repairs.

P0304 Code – FAQs

What does the P0304 code mean?

The P0304 code indicates a misfire in cylinder 4 of the engine. It can be due to various issues, including faulty spark plugs, ignition coils, fuel injectors, or engine compression.

What are the symptoms of the P0304 code?

Symptoms of the P0304 code include a rough idle, reduced power and acceleration, engine vibration, poor fuel economy, and stalling.

How can we diagnose the P0304 code?

We can diagnose the P0304 code using a scan tool to read the diagnostic trouble code and freeze frame data. A mechanic will then perform a visual inspection of the engine and perform tests on the ignition system, fuel system, and engine compression to determine the underlying cause of the misfire.

How is the P0304 code repaired?

The repair for the P0304 code will depend on the underlying cause of the misfire. Standard maintenance can include replacing faulty spark plugs, ignition coils, and fuel injectors or performing engine repairs if compression is low.

Can I still drive my vehicle with the P0304 code?

It’s not good to drive your vehicle with the P0304 code as it can cause further damage to the engine and lead to more expensive repairs. It’s best to diagnose and repair the issue as soon as possible.

How much does it cost to fix the P0304 code?

The cost to fix the P0304 code will depend on the underlying cause of the misfire and where you take your vehicle for repairs. However, standard repairs can range from replacing a spark plug or ignition coil for a few hundred dollars to performing engine repairs for several thousand dollars.

  • Latest Posts
Author , Cars Part Shop
I am Sophie Harris, a car fanatic, and reviewing cars is my life. I review them, give advice on buying, and tell you all the latest news from the automotive industry.

Request a Quote For Car Engine

Request a Quote