P0301 – Is There A Misfire In One Of Your Cylinders?

The marvel of modern engineering continually blesses us every time we get behind the wheel, though we don’t always take time to appreciate it. We take some things for granted, I guess. These days, we can rest assured that our engines would start, run, and keep going reliably for a long time, no matter the circumstance. At least, until you start seeing error codes like P0301 pop up every now and then.

Ever noticed how you’d start losing power or have that sinking feeling the engine’s going to stall and conk out at any moment now? How about sensing that crude roughness anytime you’re idling, or that the engine just sounds a bit different now? Or, more noticeably, have you been hearing your exhaust backfire on you? In that case, it’s safe to say that you’re experiencing the symptoms of a misfire.

Another fantastic inclusion in modern cars is the myriad of electronics that continually monitor how your car is doing. When it feels ill, it wouldn’t hesitate to throw a warning light (or two), just to let you know. Similarly, you might spot a Check Engine Light, and upon plugging an OBD reader in there, it’ll toss a P0301 error code at you. Or, it’ll come with a message, “Cylinder 1 Misfire Detected“.

What Is A Misfire, Anyway?

While we’re looking at P0301, perhaps we could talk more about what a misfire is, in the first place. If you’re unfamiliar with car lingo, misfires are instances where there was incomplete combustion. As you know, an (internal combustion) engine requires two key ingredients to create power; fuel and air. Of course, there are other elements within the inner workings of an engine that contribute to this.

For example, the cyclical rotation of the pistons helps to compress fuel and air together. Or, the spark plugs that induce a current to crank up the engine and keep it running. All in all, though, we keep coming back to fuel and air. Once thoroughly mixed in, a spark ignites this air-and-fuel mixture, where its combustion will produce power for an engine to function. But what if something goes wrong?

Say, incomplete combustion? Well, that’s a misfire for you. It’s when one or more cylinders wasn’t able to sufficiently combust fuel and air. In some cases, misfires also denote problems whereby there wasn’t any combustion happening at all. Note, that misfires don’t necessarily have to place the blame on the entire engine. More often than not, misfires occur in individual cylinders.

Let’s say you have a V8 engine. Commonly, misfires will usually impact only one or a couple of those cylinders at a time. Albeit, if whatever underlying issues in your engine are serious enough, then this might begin to spread to more cylinders. If not solved in time, misfires can significantly impact other components. In particular, the catalytic converters, as they’re now exposed to hot, unburnt fuel.

What Does A P0301 Error Code Mean?

When you plug an OBD scanner into your car, you may be able to extract the definition of what P0301 means in full. This error message will read something along the lines of, “Cylinder 1 Misfire Detected”. This, in short, means that you have a misfire within the first cylinder of your engine’s many cylinders in total. You’ll have to refer to your owner’s or service manual to determine which one is Cylinder #1.


If you happen to get another P03XX error code, these might also be related to misfires. Typically, your car can know exactly which cylinder is misfiring. Naturally, this would be dependent on what car you have. You’re not going to have a Cylinder #12 misfire code if your engine only has 4 cylinders, for example. Including P0301, these would be:

  • P0301 – Cylinder 1 Misfire Detected
  • P0302 – Cylinder 2 Misfire Detected
  • P0303Cylinder 3 Misfire Detected
  • P0304 – Cylinder 4 Misfire Detected
  • P0305 – Cylinder 5 Misfire Detected
  • P0306 – Cylinder 6 Misfire Detected
  • P0307 – Cylinder 7 Misfire Detected
  • P0308 – Cylinder 8 Misfire Detected
  • P0309 – Cylinder 9 Misfire Detected
  • P0310 – Cylinder 10 Misfire Detected
  • P0311 – Cylinder 11 Misfire Detected
  • P0312 – Cylinder 12 Misfire Detected


Nevertheless, it’s also possible that your car has no clue which cylinder is affected by misfiring. Or, if the misfiring occurs in numerous cylinders at a time or alternates between them. In other instances, the misfiring might only happen on certain occasions or with set conditions, such as during start-up, or if there’s too little fuel in the tank. Other miscellaneous misfire-related codes include:

  • P0300 – Random/Multiple Cylinder Misfire Detected
  • P0313 – Misfire Detected With Low Fuel
  • P0314 – Single Cylinder Misfire (Cylinder Not Specified)
  • P0316 – Misfire Detected On Startup (First 1000 Revolutions)
  • P0324 – Single Cylinder Misfire (Cylinder Not Specified)
  • P0363 – Misfire Detected – Fuelling Disabled

What Causes A P0301 Misfire Error Code, Then?

A misfire can be caused by many factors, which makes it more arduous and time-consuming to try and diagnose it. For the most part, misfiring is possible as there’s an issue with ignition or fuel delivery. As an example, if the spark plugs fail, they can’t ignite the fuel-and-air mixture. Thus, causing incomplete combustion. Or, perhaps there’s a serious disruption in the flow of fuel into the combustion chamber.

Engine misfire OBD codes combustion fuel air diagnostics troubleshooting

Without enough fuel, even the strongest sparks might not be able to induce proper combustion. Faults in ignition timing, lackluster compression ratio, and more, can all be attributed to misfiring. Frankly, the list of potential reasons why you’re getting a P0301 error code and misfires is endless. In short, we can attribute misfiring to either ignition, fuel, electrical, or other mechanical faults in the engine.

So, to best cover what might’ve prompted your engine’s Cylinder #1 to misfire, here are some of the most common causes, divided by category:

1. Spark And Ignition-Related Causes For A Misfire

Even with an ample supply of fuel and air in the engine, the lack of a spark to ignite the mixture would lead to a no-combustion situation. Or, perhaps mediocre combustion, if the spark isn’t as strong as it should be. The task of igniting the fuel and air is your spark plugs. If it can’t manage the job, you’ll find the engine essentially exhausting raw, hot, and unburnt fuel out of the tailpipes.


  • Bad Spark Plug – Spark plugs take in electricity to create a well-timed spark on its tip, which ignites the mixture of compressed fuel and air inside the combustion chamber. Unfortunately, spark plugs have a strict shelf life and require regular servicing or replacement. With an old, worn-out, or faulty Cylinder #1 spark plug, it’ll either fail to ignite the fuel or only create a weak ignition. Thus, a misfire occurs.
  • Compromised Spark Plug Wire – Your spark plugs require electricity. As such, it’s fed current from your 12V lead-acid battery through a series of wires. Over time, these spark plug wires can fail, fray, wear out, or perhaps even burn and short circuit. When this happens, electricity couldn’t flow reliably to the spark plugs. Even with pristine spark plugs, failing or faulty wires will force a weak or meager spark.
  • Defective Ignition Coil – For spark plugs to create a strong enough spark, your battery’s default voltage isn’t nearly adequate. To do this, we have ignition coils (aka coil packs), which work as a transformer that ramps up the 12V output of the battery into thousands of volts. Should the ignition coil fail, your spark plugs can only tap into a low voltage output, which is insufficient to create a strong spark.

2. Electrical-Related Causes For A Misfire

Continuing our previous point, that spark wouldn’t have happened without an electrical current. And one where its absence would cause weak or incomplete combustion. Besides that, we also have to note the various sensors, computers, and modules that manage your engine. Should they malfunction, it may also get in the way of creating fulfilling combustion for the engine to avoid misfiring.

Engine misfire OBD codes combustion fuel air diagnostics troubleshooting

  • Cracked Distributor Cap – While the ignition coils are responsible for upping the voltage from the lead-acid battery, it’s the distributor’s job to supply them to the spark plugs. While distributors are mostly a feature on older cars, they’re known to fail. This can either be due to contamination, carbon build-up, or even physical damage such as cracks. When it does, the spark plugs will be devoid of charge.
  • Untimely Ignition Timing – Ignition timing is crucial for proper combustion to take place. If it ignites too quickly or too late, there won’t be full combustion. Once more, leading unburnt fuel to exhaust out of the tailpipes. Or, in the case of igniting the fuel and air too hastily, it can lead to detonation within the engine. It’s commonly mistaken for misfires but is far more damaging over the long run.
  • Faulty Fuel Injectors – As its name makes it obvious, fuel injectors are syringe-like devices that inject fuel into the engine. They do so with precise timing as to when the solenoids within open up to let fuel in. Not to mention, being able to know exactly how much fuel is required for a good mixture. Should it get clogged up or have failed entirely, either not enough or no fuel at all will be supplied.

3. Electronic And Sensor-Related Causes For A Misfire

  • Camshaft And Crankshaft Sensor – They’re also known as the camshaft position sensor and crankshaft position sensor, respectively. Their role is to measure the relative position of the camshaft and crankshaft and report back data such as engine speed to the ECU. If either sensor were to fail, the ECU wouldn’t be able to optimally manage the engine, and its incorrect inputs may result in misfires.
  • Mass Airflow Sensor – Likewise, the mass airflow sensor is responsible for measuring the amount of air rushing into the engine. Thus, letting the ECU know just how much fuel to pump into the engine to meet the best air-to-fuel ratio. If the MAF sensor were to fail or misreport, the ECU might pump too little or too much fuel into the engine. Hence, increasing the likelihood of it misfiring.

  • Oxygen Sensor – Meanwhile, the O2 sensor (oxygen sensor) measures the amount of oxygen left behind in the previous combustion cycle. As a result, it’s able to prompt the ECU to supply more or less fuel where necessary, for optimal performance and efficiency. Should the oxygen (O2) sensor fail, there’s a strong chance of the engine running with either too much or too little fuel. Once again, resulting in misfires.
  • Engine Control UnitSpeaking of the ECU, it too may result in misfires when it (although rarely) fails. As the central command unit for your engine, it manages everything, including the volume of fuel to supply to the engine for the ideal combustion. Besides that, your engine will be far less efficient when it comes to optimizing ignition. This could lead to incomplete or poorly-done combustions.

4. Other, Miscellaneous Causes For A Misfire

  • Low Compression – In this context, ‘compression’ is the amount of pressure created inside the engine. All engines require some compression to sufficiently mix fuel and air within the combustion chamber. Without it, the diluted and free-flowing supply of fuel and air wouldn’t combust as effectively.
  • Clogged EGR – Also called the ‘exhaust gas recirculation‘, it recirculates harmful pollutants from your exhaust and pumps them back into the engine. Most cars today have one fitted, to a point where engines now require a well-functioning EGR to commit to strong combustion.
  • Vacuum Leaks – These occur when fresh air, which should’ve entered the engine, instead leaks out due to a compromised seal. The latter likely exists around the intake manifold. Without enough air, there would be far too much fuel in the engine, causing a less-than-ideal ignition.


  • Blown Head Gasket – This single gasket seals the entire combustion chamber. When it fails or is ‘blown’, it enables exhaust gases to escape the engine. Or, for coolant and motor oil to leak into the combustion chamber. As they’re not meant to be in there, they could affect the combustion.
  • Clogged Catalytic Converter – When your catalytic converters are on their way out or are clogged by exhaust fumes, they tend to overheat. This build-up of temperature isn’t good for the engine, which leads to it running roughly or losing performance. In addition, resulting in misfires.
  • Malfunctioning Exhaust Valves – These should open up once a combustion cycle ends, allowing fumes to exit the engine. Should they stick or not open, leftover gases can throw off the air-to-fuel balance. In the end, this would result in the next combustion cycle being less performant or misfire.

Aside from a P0301 diagnostics trouble code, there are also other ways that you can tell if a misfire is present:

What Are The Symptoms Of A P301 Misfire?

  • Difficulty Starting – With one or more cylinders not combusting properly, the engine might have some trouble with cranking and turn over. This is exacerbated, depending on how bad the misfires are.
  • Rough IdleWhile idling, you can sense that your car is rough, shaky, noisy, and has a lot of unwanted vibrations. Moreover, you’re able to spot that your engine’s RPM fluctuates constantly.
  • Slow Acceleration – When you press the gas pedal, there might be a momentary hesitation or stutter before it begins to accelerate. Without all of the cylinders firing right, performance will suffer.
  • Poor Performance – Speaking of, it doesn’t get any better at speed, either. There’s definitely a loss of power, with your car taking longer to get up to highway speeds or during overtakes.
  • Stalling – If the misfiring worsens, your engine might stall altogether. It might occur while driving, or during idle. Sometimes, the ECU is the one who prompts the car to stall intentionally, to protect the engine.

  • Fuel Consumption – Given that there’s incomplete combustion, you’re practically flushing away fuel down and through the exhaust pipes. In time, you’ll start to notice your MPGs dropping rapidly.
  • Check Engine Light – If there’s an error code (P0301, for example), then the Check Engine Light would surely illuminate. Should you see that CEL flashing, then it’s a sign that the misfiring has intensified.
  • Backfire – This is a scenario where air and fuel are ignited outside of the combustion chamber. Say, in the exhaust system or intake manifolds. You’ll be able to hear those popping sounds if it backfires.
  • Exhaust Smoke – With poor ignition and unburnt fuel, there’ll be far more exhaust smoke than before. Note the thick plumes of either blue, black, or white smoke, each one pointing to differing issues.

How Can You Diagnose A P0301 Misfire?

Given the sheer number of failure points that could cause misfiring, any diagnosis for P0301 will be a lengthy and tedious process. As a general rule of thumb, you can begin with:

  1. With your ODB diagnostics tool, conduct a scan of the rest of your car’s subsystems. See if there are any other accompanying error codes besides P0301. This might help expedite the process and narrow down the exact cause of the misfiring.
  2. Visually inspect the abovementioned components, and see which one may have been damaged or show signs of wear. In particular, observe the spark plugs and their wiring, the ignition coils and their wires, as well as the fuel injectors, and so on.
  3. The most typical cause for misfiring is a faulty spark plug. You can use a process of elimination by taking the Cylinder #2 (or any of the good cylinders) spark plug and swapping them with the Cylinder #1 spark plug. Give it a test drive, and see if the misfire returns.
  4. With that in mind, diagnosing a misfire would entail you testing out each component as we detailed earlier. You may need additional tools to do this. For instance, a multimeter to check if the wiring and connectors are passing through electricity properly.
  5. A more thorough diagnosis can be done, although it might require specialty equipment. Examples could include running a compression test on the engine. Or, perhaps check if there’s a vacuum leak inside the intake manifold. Once again, scan with your OBD tool to pinpoint the point of failure.

How Can You Solve A P0301 Misfire?

Unfortunately, the difficulty in diagnosis also means that solving a misfire is tricky. The solutions and costs associated with repairing your misfiring engine will depend on the point of failure. Some of the components named earlier, such as spark plugs, are inexpensive to replace. On the other hand, your head gaskets blowing, as an example, may cost you thousands for a replacement.

Therefore, there’s no singular way of solving a misfire, other than repairing or replacing the affected component which caused a P0301 error in the first place. For a bit of context:

  • Spark Plug – $50 to $100 for a single spark plug (Cylinder #1)
  • Spark Plug Wires – $150 to $250 for a set of wires for one spark plug
  • Ignition Coil – $50 to $400
  • Distributor Cap – $50 to $300 (you might have to replace the distributor rotor, too)
  • Fuel Injector – $100 to $300 (for just a single injector, but it can skyrocket pretty quickly)
  • Camshaft Position Sensor – $100 to $200
  • Crankshaft Position Sensor – $100 to $300
  • Mass Airflow Sensor – $200 to $300
  • Oxygen Sensor – $50 to $300
  • ECU – $1,000 to $3,000 (depending on the make and model of your car)
  • EGR – $250 to $550 (though it’s much cheaper if you’re able to clear out the clog instead of replacing it outright)
  • Head Gasket – $1,000 to $2,000 (depending on the make and model of your car)
  • Catalytic Converter – $500 to $2,000 (again, it’s far cheaper if you can clean the clog instead of having to replace the entire unit)

Facts on Engine Misfire and Code P0301:

  • Engine misfire refers to when one or more cylinders of the engine do not have combustion, resulting in a sudden drop in RPMs and a lack of power.
  • Code P0301 appears when the first cylinder of the engine misfires, and the powertrain control module (PCM) stores the code when it detects a larger than 2 percent increase or decrease in crankshaft rotations per minute.
  • Various factors can lead to engine misfire and the P0301 code, such as defective or worn-out spark plugs, issues with ignition or fuel system, low fuel pressure, faulty sensors, and engine compression getting low.
  • Symptoms of the P0301 code include a flashing or illuminated check engine light, rough idling or engine, difficulty in starting or accelerating, fuel smell from exhaust, and increase in fuel consumption.
  • Ignoring the P0301 code can cause serious engine damage, including damaging the catalytic converter, which can be expensive to replace.
  • It is not safe to drive with the P0301 code as misfire can cause additional damage to the car, and if the check engine light is flashing, the car is dealing with severe cylinder misfiring, and it is better not to drive further.
  • Diagnosing the issue before fixing it is crucial, and a mechanic will use an OBD-II scanner to collect all PCM fault codes and freezes frame data, test drive the car, and inspect the cylinder, spark plugs, ignition components, and fuel injectors for damage or wear.
  • Fixing the misfire depends on the cause, and the cost to fix P0301 will vary depending on the required repairs, such as replacing spark plugs, wires, ignition coils, fuel injectors, vacuum leaks, fuel pump, or pressure regulator, with estimated costs ranging from $66 to $1900.
  • It is not recommended to fix the issue on your own unless you have a mechanical background, and once the needed repair is done, the misfiring code will clear itself after some driving.

Final Thoughts On A P0301 Misfire

Oddly enough, misfires are one of the most common symptoms and experiences for many car owners, especially if they own an older model. Skipping a service or two would be more than sufficient to allow engine troubles to surface. Thus, why you’re seeing a P0301 error code. Initially, misfires might appear like a mere inconvenience. However, this is one matter that has to be addressed promptly.

Misfiring could rapidly accelerate wear and tear inside the engine, which causes permanent damage that would cost you thousands to repair. Down the line, misfires lead to the premature death of expensive parts like the catalytic converter, not to mention the entire engine. Meanwhile, solving a misfire now is relatively inexpensive, especially if it’s only affecting just one cylinder.

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