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.
What Does the P0303 Code Mean?
Diagnostic trouble code (DTC) P0303 stands for “Misfire Detected in Cylinder Number 3.” 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.
The last two digits of the code identify the specific engine cylinder that is misfiring—in this case, it is cylinder #3. Meanwhile, code P0304 indicates a misfire in cylinder #4, and so on.
What are the Possible Causes of the P0303 Code?
There are three common causes of an engine misfire. A P0303 engine code is often triggered by ignition problems, fuel delivery issues, or engine mechanical problems.
Problems in the ignition system are some of the most common reasons behind an engine misfire. Failure to transfer spark to ignite the air & fuel mixture compromises the combustion process. These misfires can start out subtle and unnoticeable, but if ignition components are left unchecked, misfires could intensify and result in severe jerking or backfiring.
Examples of ignition system problems that could cause a misfire exclusively on cylinder #3 include:
- A worn spark plug
- A damaged ignition coil
- A faulty spark plug wire (if equipped)
- Worn or failed distributor cap (if equipped)
Fuel delivery misfire
An imbalance in the air-to-fuel ratio can also cause an engine cylinder to misfire.
Examples of fuel delivery problems that could cause a misfire exclusively on cylinder #3 include:
- 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- Problems with the powertrain control module, such as a damaged injector driver or outdated software (relatively rare)
As its name suggests, this type of misfire is typically caused by worn out and defective mechanical components that cause low engine compression.
Examples of engine mechanical problems that could cause a misfire exclusively on cylinder #3 include:
- Worn valves, cylinder walls, piston rings, or camshaft lobes
- Leaking head gasket
- Damaged rocker arms
It’s worth noting that if there are also misfire codes stored for the other cylinders, the list of possible causes will potentially be different. The diagnostic process may be different as well.
But if you’ve only got code P0303 stored, you’ll want to start by focusing on issues that only affect cylinder #3.
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.