How To Fix P0304 Code For Mercedes (Meaning, Causes, Symptoms, Diagnosis)

p0304 code mercedes

A P0304 code in a Mercedes Benz is an indicator that cylinder 4 has misfired. It doesn’t mean that it’s failed, only that a misfire was detected. The light will remain on until it is deleted or until the problem is addressed.

Unless you have an OBD2 scanner that’s sophisticated enough to tell you what’s behind the cylinder 4 misfire, you’ll have to do a step-by-step progression—through the process of elimination—take it to a qualified mechanic or get an OBD2 scanner with expanded capabilities. 

Meaning Of The P0304 Code

Cylinder number four misfire is the generic meaning for code P0304 in a Mercedes—along with most other vehicle makes—but it doesn’t cover the entire issue.

There’s a lot that can go on behind the scenes to cause a misfire.

In most cases, your Mercedes will still be able to get you home or to the closest mechanic for repair, if the check engine light comes on for a cylinder 4 misfire. 

If it’s a blinking check engine light, however, that means that the problem is severe, and a breakdown might be imminent.

It’s imperative to get it parked where you can look it over or arrange for a tow. 

Read also: Can A Clogged Catalytic Converter Cause A Misfire

What Are The Symptoms Of A P0304 Code?

While they may not be immediately apparent, over time you can experience several minor issues that become more and more extensive.

  • Difficulty starting the engine
  • Hesitation when accelerating
  • Rough idling or a rough sounding engine
  • Engine light on
  • General loss of power

The first symptom you’ll likely experience is the check engine light. If you have an OBD2 scanner and it pulls a P0304 code, you should get it down to the mechanic as soon as possible. 

How To Diagnose A Cylinder 4 Misfire?

The vast majority of the time, the cause is going to be with the spark plugs or a coil pack. Other issues are more severe and less common. 

  • Fuel leak into the exhaust system
  • Bad coil pack
  • One or more faulty spark plugs
  • The timing chain is off
  • Intake air leak
  • Clogged fuel injector

The list goes on quite extensively, but those are the primary causes for a cylinder misfire on a Mercedes Benz.

Having a good OBD2 scanner really comes in handy, as it will—in the case of the cheaper, standard ones—give you the code produced by the Mercedes’ ECM.

A trip to the mechanic—even if you don’t have any work done—will generally cost you around $50+ just to get it scanned.

If you’re of a mind to knock out the work on your own, the mechanic will narrow it down for you and you can just take it from there.

There are also a lot of OBD2 scanners on the market that do much more than just give you the code your Mercedes generated. 

A more sophisticated OBD2 scanner will give you several possible culprits behind the cylinder 4 misfire and others will narrow it down even further. 

Mercedes Benz S320 – P0304 – Cylinder 4 Misfire Detected >> Check out the video below:

Estimated Cost Of Repair

Since the causes are so sporadic and random, it’s hard to get an average estimate for repairs. Depending on what the source of the problem is, it could be extensive or very minor.

If you judge only by the average cost you’ll see in a Google search, that won’t get you very far.

  • One or more spark plug replacements can run between $15 and $100 per spark plug
  • Fuel injector replacement will be between $800 and $1,500
  • Piston rings will run between $1,500 and $3,000
  • Ignition coils are generally anywhere between $110 and $265
  • Valve Springs are between $400 and $700
  • Vacuum Leak repairs will cost an average of $500
  • Timing Chain adjustments can run upwards of $2,000, most just in labor costs

You’ll also have to take into consideration that these aren’t exact prices and a Mercedes isn’t exactly a humdrum vehicle, so that will drive the price up as well.

Labor costs won’t change much based on the fact that it’s a Mercedes, but imported parts will. 

Labor costs on anything are generally between $75 and $150 per hour, however, much of the labor cost can be eliminated if you decide to do your own repairs.

DIY repair work can literally save you hundreds, if not thousands in labor costs.

The only drawback is that some of the potential repairs—timing chain, piston rings, and valve springs—are labor-intensive, require experience, and require a solid set of tools for the job. 

There’s nothing worse than taking apart half your car, spending several hours working on it, to discover that you need a new tool to finish the job.

All Things Considered

While owning a Mercedes Benz—insert model here—will change the price game a bit, everything else remains the same.

A P0304 code means the same thing in a Mercedes as it does in a Ford.

The best thing you can do when you see the check engine light is to get it scanned as quickly as possible.

Then take the necessary steps to get it fixed before a minor problem cascade into a much larger issue.

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Jeff is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Reatta. Jeff has been creating written and video content about transportation, automotive, electric cars, future vehicles as well as new, used for more than 18 years. Jeff is based in Boulder, Colorado.

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