P0304 BMW: Meaning, Symptoms, Causes, & Solutions

If you own a BMW, there’s a chance that you might encounter the P0304 engine code. P0304 is a diagnostic trouble code or DTC. The main purpose of error codes like BMW P0304, BMW P0300, BMW P0012, is to inform you about an issue with your vehicle. 

You can use an OBD-II code checker to understand what the code means. There are hundreds of DTCs other than P0304 that you can encounter. 

However, this article will be focused on the P0304 BMW error only. Upon going through this, you’ll learn how to handle your vehicle if it shows a P0304 code.

Fixing a P0304 BMW Error at Your Home

What does P0304 BMW Mean?

The DTC P0304 translates to “Cylinder 4 Misfire Detected”. This code appears when the powertrain control module or the PCM installed in your BMW registers a specific number of misfires on cylinder 4. 

What Are the Signs of P0304 BMW?

It’s not rare for cylinders to misfire, and you won’t be notified in minor cases. You’ll get the P0304 BMW code only if the fourth cylinder misfires multiple times in a day. So, it’s not as frequently seen as BMW P0174.

Some symptoms help you identify whether you’re facing the P0304 code or not. Please note that these symptoms don’t guarantee that you’re facing this specific error, but you can at least get an idea of what’s happening with your car. 

The first symptom you’re likely to face is a flashing engine light. Check the engine light to see whether the light is flashing. If you find the light flashing, it means that the car will break down at any moment. 

Another common symptom is jerking and stalling. These are often associated with poor acceleration as well. When you’re cruising at a regular speed, you’ll find the speed fluctuating unnaturally and for no reason. 

Between the two, you’re more likely to face the first symptom as it’s more common. If you find the engine light of your BMW flashing, you should get it checked immediately. 

Even if you’re not seeing the P0304 code, there’s a high chance that one or more cylinders of your vehicle are misfiring. There might even be a different underlying problem.  

Possible Causes For P0304 BMW

Possible Causes For P0304 BMW

There are a lot of things that might trigger a P0304 error, and it’s tough to figure out exactly what’s causing this error to appear on your BMW. If you have an OBD-II scanner, it’ll be very easy for you to figure out the problem. 

For those who don’t have the scanner, you can figure the problem out through a process of elimination. Although we recommend seeing a mechanic, you might even be able to fix the problem yourself if you can figure out the cause behind it. 

In case you experience any of the mentioned symptoms, you should check the spark plugs, ignition coils, and distributor cap first as these often fail.  

You checked these and found them alright, so what to do next? Check the timing chain. An off-positioned timing chain is often found as the main reason behind the P0304 error. 

Another cause can be low fuel pressure. Other than these, a damaged crankshaft sensor or throttle position sensor can trigger the error. Leaking head gaskets are also one of the common causes behind the P0304 BMW error. 

Among all the probable causes, the leaking gasket, timing chain, and low fuel pressure will put you in the worst possible scenario. Unless you’re a person with a ton of experience and knowledge, you won’t be able to fix these at home. 

The rest of the problems can be solved easily through DIY methods. For example, you can replace spark plugs as they are easily available at local auto parts stores. 

How To Diagnose P0304 BMW?

Diagnosing and fixing a P0304 code won’t be easy, and things might go sideways if you don’t have enough experience with vehicles. However, if you haven’t worked on your vehicle previously but don’t want to throw your money away, we recommend going through this guide. 

In this guide, we’ll dumb things down so everyone can understand exactly what to do. Let’s get right to it. 

Tools You Need

  • Digital multimeter
  • OBD-II Scanner
  • Screwdriver set
  • Spark plug socket
  • Sockets, ratchets, and extensions
  • Fuel pressure gauge
  • Leak down tester
  • Compression tester
  • Spark plugs (If necessary)

Diagnostic Process

To start, you need to scan your vehicle with the OBD-II scanner to check which error codes are present. If there are codes other than P0304, you need to fix them first. 

Next up, you need to check for loose connections at the wiring around cylinder four and the ignition coils. Take a close look at the ground wires too. If the ground wires aren’t connected well, they may lead to misfires. 

Faulty spark plugs and coil plugs often cause the P0304 error. Thankfully, there’s an easy way of determining if this is the root of the problem. If you’re getting the P0304 error, replace the coil plug of the fourth cylinder with the first one. Now, turn the vehicle on. 

If you get the P0301 error code this time, it’s evident that the spark plug is faulty, and a simple replacement will do the trick. 

Once you check all these and still face the error, you need to check the fuel pressure system. Check if the pressure is low or not. There’s usually a specific level of fuel pressure that your vehicle requires to function. 

However, this is a very complicated process, and fixing it by yourself isn’t recommended. In such cases, you better visit a mechanic. 

If the fuel pressure system seems alright, then you should check if any component is leaking or not. You should check these components in such cases:

  • Head gasket
  • Piston ring
  • Valve spring
  • Valve guides
  • Timing chain
  • Valve

Cost Of Diagnose

The cost of diagnosis depends on whether you’re fixing it by yourself or by a mechanic. 

Mechanics usually charge for a diagnosis time, so the charges are usually higher. You can expect to pay anywhere between $70-and $150 per hour for diagnosis time.

As for the components, here’s a list of prices for the components if they require replacement. 

  • Spark plugs: $70-$250
  • Spark Plug Wires: $150-$250
  • Ignition Coils: $230-$650
  • Vacuum Leak: $100-$200
  • Fuel Pump: $1300-$1700 
  • Fuel Injectors: $1500-$1900

How To Fix P0304 BMW

There are multiple steps to fixing any BMW error code. Firstly, you need to diagnose the vehicle thoroughly. In certain cases, you’ll find more than one error code. 

Once you figure out what’s wrong, get a replacement for that specific component. You can replace it either yourself or by a professional, and it depends on how experienced you are and how much you’re willing to spend. 

Conclusion

Fixing a P0304 BMW error can be challenging. With this guide, things will get much easier for you. 

If you’re facing this error code, take your gears and start working according to our diagnosis guide. That should be sufficient for helping you understand what’s wrong with your vehicle. 

So, what’re you waiting for? Grab your tools and get working right away! Don’t forget to share this with your friends as well!