P0304 Misfire in cylinder 4

Technical description of error P0304

Misfire detected in cylinder #4.

DTC P0304 appears when the engine control unit (ECU, ECM, or PCM) registers cylinder 4 misfire problems.

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Although general, specific repair steps may differ depending on the brand / model.

The P0304 code means that the vehicle computer has detected that one of the engine cylinders is not working properly. In this case, this is cylinder # 4.

Symptoms of error P0304

Symptoms may include:

• engine may be harder to start
• Illumination of the Check Engine light on the dashboard.
• A general drop in engine performance leading to general vehicle failure.
• The engine stalls while driving or is difficult to start.
• Reduced fuel consumption.

Causes of error P0304

DTC P0304 occurs when a malfunction causes ignition problems at cylinder level 4. The engine control unit (ECU, ECM or PCM), detecting this malfunction, causes the automatic activation of error P0303.

The most common reasons for activation of this code are the following:

• Defective spark plug or wire
• Defective coil (packaging)
• Defective oxygen sensor (s)
• Defective fuel injector
• Exhaust valve burnt out
• Defective catalytic converter (s)
• Out of fuel
• Bad compression
• Defective computer

Possible solutions

If there are no symptoms, the simplest thing is to reset the code and see if it comes back.

If there are symptoms such as engine stumbling or wobbling, check all wiring and connectors to the cylinders (eg spark plugs). Depending on how long the ignition system components have been in the vehicle, it may be a good idea to replace them as part of your regular maintenance schedule. I would recommend spark plugs, spark plug wires, distributor cap and rotor (if applicable). If not, check the coils (also known as coil blocks). In some cases, the catalytic converter has failed. If you smell rotten eggs in the exhaust, your cat's converter needs to be replaced. I also heard that on other occasions the problem was faulty fuel injectors.

Additionally

P0300 - Random/Multiple Cylinder Misfire Detected

Repair Tips

After the vehicle is taken to the workshop, the mechanic will usually perform the following steps to properly diagnose the problem:

• Scan for error codes with an appropriate OBC-II scanner. Once this is done and after the codes have been reset, we will continue to test drive on the road to see if the codes reappear.
• Visual inspection of electrical wiring for broken or broken wires and any short circuits that may have affected the operation of the electrical system.
• Visual inspection of cylinders, e.g. for worn components.
• Checking the fuel intake system to make sure it performs as expected for the vehicle.
• Visual inspection of spark plugs, which, as you know, can be disassembled and checked individually.
• Checking the intake air with a suitable instrument.
• Cylinder 4 misfire contactor monitoring.
• Checking the coil pack.

It is not recommended to proceed with the replacement of any component until all the above checks have been completed.

In general terms, the repair that most often cleans up this code is as follows:

• Replacing the spark plug in the cylinder.
• Replacing the spark plug cap.
• Replacement of damaged cables.
• Elimination of air leakage.
• Repair of the fuel injection system.
• Repair any mechanical problems with the engine.
• Troubleshooting any fuel system problems.

Although it is possible to drive a car with this error code, it is recommended to deal with this problem in advance in order to also avoid more serious malfunctions that can seriously damage the engine. Also, given the complexity of the checks, the DIY option in the home garage is definitely not feasible.

It is difficult to estimate the upcoming costs, since a lot depends on the results of the diagnostics carried out by the mechanic. As a rule, the cost of replacing spark plugs in a workshop is about 60 euros.

Frequently Asked Questions (FAQ)

What does code P0304 mean?

DTC P0304 indicates trouble starting cylinder 4.

What causes the P0304 code?

The most common cause for this code to activate is faulty spark plugs, as they are worn out or clogged with grease or dirt buildup.

How to fix code P0304?

The wiring harness and spark plugs should be inspected first, replacing any faulty components and cleaning the area with a suitable cleaner.

Can code P0304 go away on its own?

Unfortunately, this error code does not go away on its own.

Can I drive with code P0304?

Driving a car on the road, while possible, is not recommended if this error code is present. In the long run, much more serious problems may arise.

How much does it cost to fix code P0304?

On average, the cost of replacing spark plugs in a workshop is about 60 euros.

How to Fix P0304 Engine Code in 3 Minutes [2 DIY Methods / Only $4.33]

Need more help with your p0304 code?

If you still need help with DTC P0304, post a question in the comments below this article.

NOTE. This information is provided for informational purposes only. It is not intended to be used as a repair recommendation and we are not responsible for any action you take on any vehicle. All information on this site is protected by copyright.