What Does the "Engine Code P0300: Random or Multiple Cylinder Misfire" Mean?

If your car is showing the P0300 engine code, you’re dealing with a problem with the cylinder(s) misfiring. Here's how to diagnose engine code P0300 and fix it.
Written by Tiffany Leung
Reviewed by Melanie Reiff
If your car is showing the P0300 engine code, you are dealing with a cylinder misfiring issue. This code is serious, and you should have your vehicle inspected as soon as possible to avoid damage to your catalytic converter.   
Diagnostic trouble codes (DTCs) give you a general indication of issues with your car’s engine. You can use an OBD-II code reader to figure out what the specific engine codes mean and get a start on tackling the problem.
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What does the engine code P0300 mean?

Definition: Cylinder misfire detected—random cylinders
The P0300 engine code indicates a problem with your car’s cylinders misfiring
The cylinders are where the fuel is combusted to generate power, and misfires happen when there is an insufficient amount of fuel burned or issues with the spark plug. In extreme cases, this can cause damage to your
catalytic converter

How much will it cost to fix engine code P0300?

Running a diagnostic for a P0300 will cost about an hour of labor and run you between $75 to $150 at the shop.
If you a
spark plug replacement
, the total cost for parts and labor may be anywhere from $250 to $900.

What can cause the P0300 engine code?

The most common cause of cylindrical misfiring is related to the spark plugs.
Spark plugs are responsible for igniting the air/fuel mixture in the cylinders to create small explosions, which powers your engine. 
Other potential issues that could cause this engine code include: 
  • Faulty ignition coil(s) 
  • Clogged or faulty fuel injector(s) 
  • Fuel injector harness is open or shorted 
  • Fuel injector circuit has poor electrical connection 
  • Ignition coil harness is open or shorted 
  • Ignition coil circuit has poor electrical connection 
  • Insufficient cylinder compression 
  • Incorrect fuel pressure

Common symptoms of the P0300 engine code

There is a possibility that you won’t notice anything aside from the
check engine light
turning on. Other potential signs to watch for with a P0300 include: 
  • Lack or loss of power
  • Hard starting
  • Engine hesitates
If your cylinders are indeed misfiring, the engine will also run poorly and will be
or bucking
You may see other codes show up alongside engine code P0300, too. Engine codes P0301 to P0308 all deal with
engine misfires
, so they could be seen.

How serious is the P0300 engine code? 

The P0300 engine code is a critical issue. You should get a diagnostic check immediately (on the same day if possible). 
Cylinders that continue misfiring could lead to serious damage to the catalytic converter, which is extremely costly to repair.

Can I fix the P0300 engine code myself?

In some cases, you can fix the cause of a P0300 engine code at home, but you must diagnose the issue correctly before you begin any repairs. 
Depending on the issue, you may have to do the following:
  • Replace the spark plug intake gasket
  • Clean or replace the spark plug
  • Clean or replace the ignition coil
If you’re not sure what repairs your car needs, bring your car to a professional to complete a thorough diagnostic inspection and repairs.

Repairing the P0300 code

If you do decide to repair the P0300 code by yourself, you can follow these steps:
  • Identify which cylinder(s) is misfiring before proceeding to repairs and follow the below steps as required.
  • Replacing the spark plug
  • Remove the spark plug from under the plug covers on the engine
  • Check the spark plug spacing with a spark plug gapper (0.024 to 0.071 inches)—use the gapper to restore the correct spacing if needed
  • Clean or replace the spark plug if it is damaged
  • Replacing the ignition coil 
  • Remove ignition coil from above the spark plug
  • Check the ignition coil for any stains or damages
  • Clean the ignition coil if it is dirty or replace it if it is damaged

Finding insurance for your vehicle

Car repairs can be costly—there’s no way around it. If you’re looking for a way to free up some extra cash for car maintenance, try finding a more affordable
car insurance
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