P0300 – Meaning, Causes, Symptoms, & Fixes

Code P0300 Definition

Random/Multiple cylinder misfire detected.

What Does P0300 Mean?

P0300 indicates that one or more cylinders are experiencing misfires. A misfire occurs when an insufficient amount of fuel is burning 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 one 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.  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:

How To Diagnose P0300
  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.
  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:
    • 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.
    • 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.
  5. 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:
    • Broken valve spring
    • Broken piston ring
    • Worn valve guides
    • Burned valve
    • Timing chain or belt skipped tooth and engine is off time.
Was this post helpful?
Let us know if you found this information useful!
Yes325
No24

Comments 11

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.

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.

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

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

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.