P0300 – Meaning, Causes, Symptoms, & Fixes

Code P0300 Definition

Random/Multiple cylinder misfire detected.

What Does P0300 Mean?

P0300 indicates that two or more cylinders are experiencing misfires. A misfire occurs when an insufficient amount of fuel is burned in a cylinder. The efficient burning of fuel is essential to engine operation as the combustion of fuel is what provides the energy to power the engine. A misfire from two or more cylinders can be caused by many reasons from a faulty ignition system, fuel system, or internal engine failure. When P0300 occurs, it should be fixed immediately as long term driving with engine misfires could cause consequential damage to your engine and catalytic converter(s).  Many times, P0300 occurs when there are worn out spark plugs, spark plug wires, or a faulty ignition coil.

P0300 Symptoms

  • Check Engine Light is on
  • Check Engine Light flashing
  • Engine runs rough and shaking
  • Lack of power from the engine
  • Fuel smell from the exhaust
  • Hesitations/Jerking when accelerating

P0300 Causes

(* = Most Common)

  • Faulty or worn spark plugs *
  • Faulty spark plug wires or coils *
  • Distributor failure *
  • Faulty fuel injector 
  • Vacuum leak
  • Low fuel pressure
  • Camshaft sensor defective
  • Crankshaft sensor defective
  • Engine timing off
  • Leaking head gasket
  • Low engine compression
  • Poor quality fuel

Code P0300 Severity – Severe

P0300 should be repaired immediately. Ignoring this error could result in ignition failure, catalytic converter damage, and unsafe/dangerous conditions while operating the vehicle.

Code P0300 Common Diagnosis Mistakes

Loose fitting electrical connectors and broken or disconnected vacuum hoses are often overlooked.

Code P0300 Diagnosis Steps

Tools Needed to Diagnose:

Tools You May Already Have:
Tools You May Need (FIXD’s Top Picks From Amazon):

How To Diagnose P0300

Difficulty of Diagnosis and Repair – 2 out of 5

  1. Use FIXD to scan your vehicle to verify P0300 is the only code present. If other codes are present, they must be addressed first.
  2. Check for loose connectors at the ignition coils or for damaged wiring. Look for loose engine ground wires as well. These can cause random misfire conditions. Tighten or connect where necessary.
  3. Check the condition of your spark plugs and spark plug wires. 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 identify a fouled spark plug, How to test spark plug wires, How to gap spark plugs, How to replace spark plugs)
  4. 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.
  5. 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)
  6. Check that 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)
  7. 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. Some common mechanical problems that cause misfire can be:
    • 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.

Estimated Cost of Repair

For error code P0300, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair. 

  • Spark plugs $40-$640 (some cars require Intake manifold removal)
  • 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

Was this post helpful?

Comments 38

Betty Conley

July 16, 2018

I had no idea I had a problem until the “check engine “ light come on and I looked it up on FIXD. I could have done some serious damage. Fortunately the car is still under warranty, but I wish I knew of one of your FIXD mechanics here for future reference.

Khali

May 3, 2019

My dad is a mechanic he fixes car trucks and

thomas l street

June 8, 2019

where is his shop

Kat

October 9, 2019

So does this FIXD gadget tell you exactly what’s wrong,

Bill

June 23, 2019

All good info but in my case, the misfires are all on one bank, 4.7 l v8 cyl 2,4, 6,8

Danny

August 9, 2019

Timing chains

Betty Conley

July 17, 2018

My car is still under warranty so I took it to my local Subaru dealer in Factoria, Washington, and he doesn’t have a clue because I turned off the check engine light.
Could I get a phone no. so he can call your mechanic?

FIXD Marketing

July 18, 2018

Hi Betty,

There is actually a history of which check engine codes are triggered in the FIXD app, so if you scanned your car with the FIXD sensor/app you can look back on situations similar to this! If not, you will need to wait for the Check Engine Light to come back on and diagnose it at that time.

Thank you,
The FIXD Team

Marina

October 22, 2018

Hi Betty,
What do you mean triggered in the FIXD app?
My check engine light came on and I used my FIXD to see why. The P0300 codes on all cylinders came up. I had it towed to garage immediately.

Steve

January 15, 2019

What did they find as your problem?

June LejeuneJune

May 30, 2019

How do u turn off engine light have inspection tom

Ervin Tolliver

May 7, 2019

What was the issue?

Lee tsosie

August 22, 2019

Flashing engine light

James Husak

September 30, 2019

After receiving a code of misfire of one or more cylinders, I Went and purchased all eight ignition coils and plugs. Of course I disconnected battery and I’ll have to wait until engine light comes back on and rescan and hopefully I fixed the problem. If not I just may sell the truck. I don’t need a money pit.

Gabriel

November 25, 2019

Did it work after u replaced egnition coils and spark plugs?

Brian Johnson

August 5, 2018

I have a C320 sport coupe 2003 lost power coming from work car eventually shut off. Before this happened check engine light came on took it to o reilys. They scanned it said i needed two sensors. I bought a scanner myself it’s been parked for a while trying to find a good mechanic is like impossible. Question im getting p0300 p0301 p0302 p0303 random misfires on 3 cylinders. I ordered crankshaft sensor camshaft sensor i cleaned the mass air flow sensor myself. I started with the basics i changed all spark plugs all wires all coils and filter still getting rough idle car starts for seconds then shuts off. Is it possible the sensors i bought should be my next step or compression test?

Betty Conley

August 16, 2018

The check engine came on again and I did not turn it off this time. Took it to my SUbaru dealer in Eastgate WA and they repaired it within an hour. Great service. Just remember – DO NOT TURN THE ENGIN LIGHT OFF until you get to your dealer.

Charles

October 18, 2018

Rats chewed the wires off top of gas tank, spark plug, ensulations.replace and tape wires. Spray rubbery on missing ensulactions. Less then 67,000 miles. What to do now?

Muhammad nadeem ahmed

October 21, 2018

Very help full video Thanks

Gary franklin

July 11, 2019

My check engine light comes on at 3000 RPMs and I don’t know why I cannot get any mechanic that can tell me what the problem is I’ve done change my mass airflow sensor all my coils my plugs my plug wires my knock sensors my cam sensor a couple more sensors I don’t even know the name of right now and it’s still at 3000 RPMs the check engine light comes on and starts flashing and it starts running rough what do you think is wrong with it please I need some help

Brandoll Rios

September 19, 2019

I’m pretty sure it’s your valve lash clearance is tight.

Robert Rodriguez

October 26, 2018

Buenas tardes tengo un problemita como mi carro que cuando lleno el tanque el carro le cuesta prender nadamás que puede ser

Katherine

November 2, 2018

I have a 99 Toyota Tacoma 2.7 and we changed the injectors and it was running great still had a check engine light on so plugged it in and it instantly ran like shit and threw like 10 codes now will barley start or read any codes?! Help I am gunna unplug battery and check my fuses

Meh Nah

February 24, 2019

Did you make sure you plugged them all back in tight check ur fuel pressure

Andy

November 28, 2018

Hey my names andy im working on a nightmare truck, my boss sunk his 03 gmc 1500 5.3l in 12 feet of water i finally got it running and alive again. Oil change fuel pump and filter in tank change spark plug change wires and coils. Air filter mass air flow changed. I now have one code only that keeps popping up with rough idle random misfire code p0300 thats the only code. Oh replaced and relearned the ckp sensor. This thing has stomped my hined end! Im a semi truck mechanic have been for 20 yrs i dont work on gas engines any help would be nice.

Allen

December 28, 2018

Andy, that 0300 means you have a misfire one or more cylinders. in addition it should have told you what cyl. It is probably a plug, plug wire, coil or in the solid state ignition. My BMW has a separate coil for each cylinder and they fail on a regular basis. give me a ford anytime over this piece of crap. You should simply use a screw driver and ground out the plugs to find the faulty cyl.

Anthony

May 26, 2019

Why do you mean “use a screwdriver and ground out the plugs to find faulty cyl”? I need to try this but not sure how. Please help

Wendy

January 15, 2019

Help! As soon as I put gas in the car today I got this notice:
Code P0300 Severity – Severe

However, the scan has not reappeared at all again and says everything is fine with the car. Does the warning only appear once and then disappear completely? I do not have a check engine light or anything.

Meh Nah

February 24, 2019

If you don’t have the light ur fine you probably just had some bad gas

Phillip Stillinger

January 18, 2019

I have a 2005 Chevy express van 4.8 I have changed plugs wires coils and cleaned injectors. I still have a slight miss and engine light still comes on. I also checked fuel pump pressure and is good. What is going on?

Butch Giusto

May 14, 2019

I have a 2003 Nissan Murano with lots of miles (193K and counting). The Po0300 code came on a couple of times before and it turned out to be a faulty coil. Since there are 6 cylanders and each has a separate coil, I am now on my 4th coil replacement. It would have been cheaper to replace them all at once, but coming up with $250 each time eas easier than the almost $900 originally quoted to me. So…thanks to FIXD, I can repair one and keep driving until the next one goes. Being on fixed income, this has kept me driving without a replacement car needed and allowed me to make an informed decision on when I absolutely have to get repairs. Thanks for the gadget and app.

David Brown

September 30, 2019

Check on Amazon for your auto parts, I have and lately my parts have been a lot cheaper and they ship right to your house.

Tono Carrasco

June 3, 2019

Hi there FIXD team! I own a 2016 Dodge Gran Caravan. I got the P0300 code with the “check engine light” on…I opened the car hood and a realized the power steering liquid was at its minimum level. I am not using the car right now and I want to rule out the “easy causes” first…Do u think this might be the reason? A few more details in case u might help:
1. The first time the “check engine light” came on steady was while driving, say on Friday AM.
2. A few minutes later, the light went off.
3. Friday PM, while driving, the “check engine light” came on blinking.
4. I stopped the car 10-15 min. Drove again and the light was off.
5. By the end of my drive (10 more minutes after i stopped), while parking “check engine light” came on blinking.
6. Since then I have not used the car.

Thank you in advance!

Keasa

June 28, 2019

I have a Chrysler 303.5 2006 I’ve had this random misfire code for about a month now and I have checked and fixed everything and then some and I am still having the code every mechanic I take it to a stumped because the car runs just fine when it’s parked or if I sit there with my foot on the break it idols and shakes I have checked for low fuel pressure vacuum leaks EGR system coil spark plugs and wires ignition module complete oil change and flush replaced cam and crank sensors I’ve even replaced my computer the code was gone for over a week and then randomly started flashing almost 2 weeks later .

asprite

July 26, 2019

You got yourself a new reader.

josh handy

August 8, 2019

I have a 2009 hummer h3t 5.3, it was running absolutely fine until i changed plugs and wires, now i have a maf sensor code and random multiple misfires…I have confirmed plugs and wires are correct and everything is properly fitting…what could be causing this..i changing the maf tomorrow morning..hope thats all it is

Ethan Mullis

August 28, 2019

I have a 1997 Chevy Silverado 1500 5.7L vortec and I have a random misfire I have changed the plugs and wire’s and cap and button and the ignition core and it’s still has a random misfire. What do I need to do?

Mike

October 7, 2019

Scrap it! Lol. Just kidding

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