P0301 – Meaning, Causes, Symptoms, & Fixes

Code P0301 Definition

Cylinder 1 misfire detected.

  • Commonly associated with codes: P0300

What Does P0301 Mean?

P0301 indicates that cylinder number 1 is 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 P0301 occurs it should be fixed immediately as long term driving with engine misfires could cause consequential damage to your engine.  Many times P0301 occurs when there are worn out spark plugs, spark plug wires, or a faulty ignition coil.

P0301 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

P0301 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 P0301 Severity – Severe    

P0301 should be repaired immediately. Ignoring this error could result in ignition failure, catalytic converter damage, and unsafe/dangerous conditions while operating the vehicle.

Code P0301 Common Diagnosis Mistakes

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

Code P0301 Diagnosis Steps

Tools Needed to Diagnose:

How To Diagnose P0301

  1. Use FIXD to scan your vehicle to verify P0301 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. If your vehicle is equipped with individual coil packs instead of spark plug wires, start by removing the cylinder 1 coil and swapping it with the cylinder number 4 coil. If the misfire moved to cylinder number 4, then you have determined that the coil pack is faulty and needs replacement. Replace spark plugs and spark plug wires/ignition coil packs if needed and recheck for misfires.
    1. How to identify a fouled spark plug
    2. How to test spark plug wires
    3. How to gap spark plugs
    4. How to replace spark plugs
    5. How to swap ignition coils
  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:
    1. 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.
      1. How to check fuel pressure
    2. 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.
      1. How to check fuel injectors by ear
      2. How to check fuel injectors with a digital multimeter
  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:
    1. Broken valve spring
    2. Broken piston ring
    3. Worn valve guides
    4. Burned valve
    5. Timing chain or belt skipped tooth and engine is off time.
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Comments 2

Sylvan Scott

August 4, 2018

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

Geoffrey Jones

November 12, 2018

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.