Ignition Systems ControlOBD2 Codes

P0301 – Meaning, Causes, Symptoms, & Fixes

P0301 Cylinder 1 Misfire Detected

What Does Code P0301 Mean?

  • P0301 definition: Cylinder 1 misfire detected.
  • Issue Severity: SEVERE – Stop driving immediately
  • Repair Urgency: Fix this code immediately (same-day if possible) to avoid ignition failure, catalytic converter damage, and dangerous conditions
  • Diagnosis: A misfire can be caused by anything from faulty spark plugs to low engine compression. Because there are so many variables that could cause a misfire, the best cost savings is to take your car into a shop to have it diagnosed as quickly and accurately as possible.

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Your vehicle moves when gasoline is burned and power is generated inside a chamber known as the cylinder. Most engines have a 4, 6, or 8-cylinder engine, where more cylinders typically mean more power. Power is generated by pistons that move up and down while fuel is ignited at very specific times. A misfire typically occurs when the timing of this ignition is off.  P0301 indicates that cylinder #1 is experiencing misfires.

P0301 Causes

Misfires can be caused by many reasons from a faulty ignition system, fuel system, or internal engine failure. The most common reason for this to happen is faulty or worn-out spark plug coil packs, especially if it’s been a while since you had a tune-up.

  • Faulty or worn spark plugs and/or spark plug wires
  • Ignition issues, including failing or damaged ignition coils 
  • Distributor failure 
  • Faulty fuel injector
  • Vacuum leak
  • Low fuel pressure
  • Camshaft and/or crankshaft sensor defective
  • Engine timing off
  • Leaking head gasket
  • Low engine compression
  • Poor quality fuel that is old or contaminated

P0301 Symptoms

  • Check Engine Light is on or flashing
  • Engine runs rough, hesitates, or jerks when accelerating
  • Drivers may not notice any adverse conditions when driving
  • In some cases, drivers may experience decreased fuel economy, fuel smell from exhaust, rough idling, or lack of power from the engine
  • Commonly associated with error codes: P0300, P0302, P0303, P0304, P0305, P0306, P0307, P0308

How Do I Fix Code P0301?

With a misfire fault, the first step is to get it diagnosed to figure out what is causing the engine to misfire. 

If your vehicle is misfiring and you’re not comfortable diagnosing this issue at home, we recommend finding a RepairPal certified shop nearby to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

Right shop, right price

We've partnered with RepairPal to recommend certified and trustworthy shops in your local area. 

  • Upfront cost estimates
  • Minimum 12-month, 12,000-mile warranty
  • Fair price guarantee

How Much Does It Cost to Fix Code P0301?

P0301 can be caused by anything from old spark plugs to vacuum leaks to poor engine compression. It’s impossible to give an accurate estimate without properly diagnosing the issue first. 

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0300 code.

Possible Repair Costs for P0301

Once properly diagnosed, P0301 may require one or more of the following repairs to resolve the underlying issue. These prices are based on national averages and include parts and labor. Your cost may differ depending on your location and type of vehicle.

  • Spark plugs: $66-$250
  • Ignition Coils: $230-$640 (some cars require Intake manifold removal)
  • Spark plug wires: $180-$240
  • Fuel injectors: $1500-$1900
  • Vacuum leak: $100-$200
  • Fuel pump: $1300-$1700
  • Fuel pressure regulator: $200-$400

DIY Steps to Diagnose Code P0301

Engine code P0301 could be caused by a number of things, including faulty spark plugs, faulty ignition system, distributor failure, and more. If you’d like to try to fix code P0301 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Keep in mind this is an intermediate-level diagnosis and repair and not recommended for beginners. Diagnosis requires more specialized equipment beyond what the FIXD Sensor can provide and it can be a time and labor-intensive process for inexperienced DIYers.

DIY difficulty level: Intermediate

This repair requires mechanical knowledge and is not recommended for beginners.

Tools/parts needed (our top picks from Amazon):


Use FIXD to scan your vehicle to verify P0301 is the only code present. If other codes are present, they must be addressed first.


Look for loose engine ground wires as well. These can cause random misfire conditions. Tighten or connect where necessary.


Worn and old spark plug wires are common causes of random misfires. Replace spark plugs and wires if needed and recheck for misfires. 

> How to replace spark plugs in 4 easy steps

> How to identify a fouled spark plug

> How to test spark plug wires

> How to gap spark plugs


If you have determined that your ignition system is operating correctly, there may be a problem within your fuel system that is causing the random misfires. The following should be checked to ensure the engine is getting the proper amount of fuel.

  • Check fuel pressure: Low fuel pressure can cause intermittent misfires on multiple cylinders. When the pressure is below the specification, the engine does not receive the proper amount of fuel and will start to lean misfire. The fuel pump or fuel pressure regulator could be the source of the low fuel pressure.

> How to check fuel pressure

  • Check fuel injectors: Make sure the fuel injectors are functioning properly and activating. Random misfires can be a sign of faulty or clogged fuel injectors that need to be replaced. Also, check that the fuel injector wiring is not damaged and is connected properly.

> How to check fuel injectors by ear

> How to check fuel injectors with a digital multimeter


If the ignition system and fuel system checks out, you may want to perform an engine compression test and leakdown test to see if there are any mechanical problems causing your misfire. 

Common mechanical problems that can cause misfires:

  • Leaking Head Gasket
  • Broken valve spring
  • Broken piston ring
  • Worn valve guides
  • Burned valve
  • Timing chain or belt skipped tooth and engine is off time.

Common P0301 diagnosis mistakes

Loose fitting electrical connectors and broken or disconnected vacuum hoses are often overlooked. Oxygen sensor(s) are another common misdiagnosis for P0301.

Still Need Help Fixing Code P0301?

If you’ve followed the steps above and are still experiencing misfires or check engine code P0301, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price.


Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

Justin Hughes
Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

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    1. Thanks! CEL came on, and the truck was idling loud and losing power. Switched out the spark plug and it’s running like butter.

    2. Accidently over rev’ed the engine when I started it. Immediately got a flashing CEL with audible alarm. Engine ran rough when at idle speed. Checked the diagnostics using FIXD and gave me a code indicating cylinder #1 was misfiring. On the road, at about 40 mph, the engine ran very rough and seemed to be losing power. Most likely I will have to take it to the Dodge dealer ASAP to get all problems associated with over rev resolved. Unfortunately, I think it’s more than just a bad spark plug this time.

      1. And what did u find my friend ? Because I had the same problem before an hour ago , but the CEL gone and everything went so fine , it only flashed for 4 seconds .

        1. Just purchased my vehicle, it drove fine, appeared to be very decent purchase. The next morning started the vehicle no dashboard light , no radio dash light and engine hesitation. Purchased the FIXD sensor gave me the P0301 diagnosis

    3. The rough shaking and and idel only happens on startup. After that it run smooth and never misses at high speeds

    4. I just had the plugs and all the gaskets changed, as well as all fluids flushed and replaced, ran diagnostics
      With fixed module, and it the up a p0301 code came up! The people that did the work told me BMW requires a “special” diagnostic equipment, THAT IS BULL#$@&!

      1. BMW does use proprietary codes. The P codes do not always give you a correct cause for the SES lamp. I ain’t saying bring it back to the same place if you’re not comfortable but they were not dishonest about needing BMW specific code reader.

    5. I have the same problem! Code P301 came up meaning Cylinder 1. I have a 2005 Impala. This my second time changing out that same spark plug. The first spark plug I bought had broke off in there. And my mechanic got it out and put another one in. Now my car misfiring again and the same code popping up. What else could be wrong? Someone please help me!! Thanks!!

      1. I just had a new set of spark plugs put in about 2 months ago and just the other day my engine light came on. I hook my diagnostic OBD2 reader up and po301 code came up. (I was told that you also need to check the spark plug wires and to see if you have a bad engine coil that can be causing a bad spark or you’ll have the same problem again after you put in a new spark plug cause you didn’t change the spark plug wires are bad engine coil.

    6. My code went away, should I still change my coil packs and spark plugs or just wait till it pops up again?

      1. I would go ahead i had the same p0301 code pop up and it was a misfire on the coil pack

        1. As I was getting on the interstate I put my foot on the gas pretty hard to try and build speed while merging and I was at around 75 to 85 mph. At that speed I had to hit the gas hard again raising my rpms really high and before I could get out of the way of a truck the check engine light came on for about a mile down the road then went off. Trying to figure out if I should worry about my engine since it was this code that I’m getting.

          1. Patrick,

            I’m having the exact same issue. Were you able to get the issue solved?

    7. Working on a 2014 Camaro right now with the same code. Trying to switch the coil pack and plug to a different cylinder to check if it’s plug and coil pack. If it reads cylinder 1 should you change the whole side? Cylinders 1,3 & 5

      1. If it’s the plug then they probably are all in need of change coil packs I would look at a pack by pack basis, don’t forget to check vacuum leaks and injector o rings could be the culprit in fact there are a lot of things that can cause misfires happy hunting.

      2. When the PO301 code came up on my 2005 Taurus I pulled one plug to see what shape they all might be in because the coil and wires were fairly new. It was pretty worn, so I bought six new ones. Out of curiosity I replaced #1 first and retested. The problem was still there, but after I replaced the rest it ran fine and the light did not come back on. I don’t know if the tool misdiagnosed which cylinder was bad, but it makes sense that when all plugs are (probably) the same age, replace them all.

    8. My Mitsubishi Outlander 2.0 from 2003 gives a p0301. The engine runs rough at idle, but runs fine at higher speeds.
      All spark plugs, spark plug wires, both coil packs, both lambda’s, air filter and the cooling fluid temp sensor have been replaced with new parts and the MAF has been changed out with a used part. The error code and problem, rough idling, persist. Replacement of parts is getting quite expensive. Is there any way to determine the exact cause of the error?

    9. I drive a 2003 Chevy Trailblazer LT. The P0301 code came up a few days ago I have changed spark plugs, since and it continues. I barely have any power at high speeds and it takes what feels like forever to reach a high speed. It was running really rough even while idling but that issue is from what I can tell done since I did an oil change and changed the air and fuel filters. I just bought this car a month ago and am relying on it to last awhile. Should I check the coils next or what should my next step be in order to salvage my vehicle.

    10. My Check engine lite came on , so I ran a check with my Fixit . It said I was running lean on both banks. It said it wasn’t very serious so I let it ride for a few day. On the third day it started flashing. I read a little bit about it on line. One article said my Mass Airflow sensor could possibly. It said to get a can of Mass Airflow sensor cleaner. This turned of to be just electronic circuit cleaner. I sprayed my sensor rather liberally. I let it dry and reinstalled the sensor and cleared the codes. Then I started the engine. No Check Engine light ,no rough idle. It hasn’t recurred in a week. Pay to research your Codes

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