Jeep P0300 – Meaning, Causes, Symptoms, & Fixes

Jeep Code P0300 Definition

Random/Multiple cylinder misfire detected.

What Does Jeep P0300 Mean?

Jeep code 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 in your Jeep. 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 the engine in your Jeep.  Many times P0300 occurs when there are worn out spark plugs, spark plug wires, or a faulty ignition coil.

Jeep 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

Jeep 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

Jeep Code P0300 Severity – Severe

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

Jeep Code P0300 Common Diagnosis Mistakes

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

Jeep Code P0300 Diagnosis Steps

Tools Needed to Diagnose:

  • Tools You May Already Have:
  • Tools You May Need (FIXD’s Top Picks From Amazon):
    • FIXD
    • Digital multimeter
    • 5/8in. Spark Plug Socket
    • Ratchet, sockets, and extensions
    • Fuel pressure gauge
    • Compression tester
    • Leakdown tester
    • Spark plugs
    • Spark plug wires

How To Diagnose Jeep Code P0300

  1. Use FIXD to scan your Jeep 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.

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Comments 6

Moe

July 7, 2019

I have a missfire and p0300 code. Changed spark plugs coils and cleaned out fuel injectors. Checked the gas tank and for any leaks but nothing is wrong. I disconnected the o2 sensors and still have the missfire. Also checked out the air intake . What could it be ??

Shane

January 15, 2020

Have the same problem did you figure it out?

kiara

February 25, 2020

Do you figure it out? I was told the crankshaft sensor b UK t haven’t done it yet

Jared Thomas

May 13, 2020

I’ve been having the same issue, p300 and p0052 codes. I had replaced the plugs, wires, and coil. I used a reader and found out it was cylinder 1 and 6 so I replaced those plugs again. I still have the same issues however. My next stop is the O2 sensors.

Dan Rodgers

January 27, 2020

I. Hanged my spark plugs and my ignition coils and the Jeep still registered cylinder 1 misfire and multiple misfires. The next thing to do is change the fuel injectors and see what happens. Fingers crossed !!

Bridgette Liggons

February 18, 2020

The engine light on my ’09 Jeep Grand Cherokee came on Sunday afternoon. On my way to Firestone this morning to get it checked out, the engine light started flashing and the vehicle felt like it was going to stall. I pulled over to an O’Reilly’s which was on the way. The OBD II scan presented O2 sensor and multiple misfires, P300, fault codes. So I chanced it and continued my trek. Firestone confirmed the finding. They replaced 6 spark plugs, 2 O2 sensors and performed a fuel cleaning. I’m good now…

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