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A misfire occurs when there is an insufficient amount of fuel burning in a cylinder. Since the way the engine runs relies heavily on the proper functioning of its cylinders, a misfire can cause big problems. That’s why the OBD-II code P0303 is considered a serious issue and should be addressed immediately.

Find out what you need to know about this trouble code.

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The P0303 code belongs to a series of diagnostic trouble codes starting from P0300 that refer to an engine misfire or incomplete combustion in one of the engine cylinders.

What Does the P0303 Code Mean?

Diagnostic trouble code (DTC) P0303 stands for “Cylinder 3 Misfire Detected.” The code indicates that the powertrain control module (PCM), has counted enough misfire events on cylinder 3 to store the misfire code for that cylinder.

Cylinder number 3 would refer to the third cylinder as the cylinders are numbered.

To learn more about firing order, read our explanation here.

For an in-depth discussion of how the engine computer knows which cylinder is misfiring, you can read more here.

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A broken spark plug can trigger the code P0303.

What are the Possible Causes of the P0303 Code?

A multitude of possible causes can set a misfire resulting in a stored P0303 trouble code. You can learn more about how misfires happen here. Here’s a list of possible causes for the P0303 code:

Ignition system problems, such as:

Fuel delivery issues, such as:

  • A faulty fuel injector
  • Wiring issues with the fuel injector circuit (e.g., loose connections, damaged wires)
  • Problems with the powertrain control module, such as a damaged injector driver

Engine mechanical problems, such as:

  • A leaking valve
  • A worn piston ring, a damaged piston or damaged cylinder walls
  • A worn camshaft lobe or damaged lifter
  • A leaking head gasket
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Reduced vehicle performance can be a sign of P0303 code.

What are the Common Symptoms of the P0303 Code?

There are several P303 engine misfire symptoms to look out for. Below are some of them:

  • Check Engine light is illuminated or blinking
  • Vehicle jerks or hesitates during acceleration
  • Reduced performance exhibited through rough idling, stalling, reduced fuel economy, and loss of power

How to Diagnose the P0303 Code

Most OBD-II codes have many possible causes. Because of this, diagnosing the exact cause will be a challenge. For the engine code P0303, there are several online resources that can help you accurately assess the situation.

We recommend that you check out the video below for some helpful information to help you troubleshoot the P0303 code.

How to Fix the P0303 Code

With the wide variety of possible causes for the error code P0303, there isn’t one surefire way to fix it. There are a few different repair options, and how you address the code will depend on the exact cause.

That’s why the key to effectively fixing the P0303 code is to diagnose it properly and pinpoint the exact cause.

Before proceeding with diagnosing or fixing any trouble codes, remember to consult your owner’s manual or service manual for more information on how to go about certain repairs.

Chilton repair manuals are useful but getting an ALLDATA subscription has even more benefits for DIYers like you. A single-vehicle subscription from ALLDATA comes in handy because it provides you with the detailed factory repair information that you need.

Products Mentioned in this Guide

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

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File Under : OBD-II Trouble Codes
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