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P0303 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

OBD2 units are incredibly valuable in the world of automotive mechanics. These brilliant units give us greater insight into the issues a vehicle may be facing, and give mechanics an idea of where to start and what to look for when diagnosing and treating an error or issue.


A P0303 trouble code via your OBD2 scanner indicates you have a cylinder 3 misfire detected.


A P0303 code displays on your OBD2 computer when your engine control unit (ECU) detects multiple different misfires from cylinder 3. The misfires cause the engine control unit to turn on the check engine light and put the vehicle into what is known as “failsafe mode” to prevent further damage to the vehicle. The check engine light will stay illuminated until this issue is repaired. After you are able to fix this misfiring issue, the  P0303 trouble code should no longer come up on your OBD2 scanner.


There are a few primary problems that can cause a  P0303 trouble code to display on your OBD2 scanner unit:

  • This can be caused by faulty or damaged spark plugs.
  • Fuel injection issues are another common cause for this problem.
  • This can also be caused by cap and rotor, plug wires, or coil pack issues, depending on what the vehicle in reference is equipped with
  • Other engine issues that are mechanical in nature
  • Air leaks in the intake

If you have found that a vehicle has a P0303 code, it could have easily been caused by any number of the above issues.


Due to the severity of this issue, a P0303 trouble code has several different symptoms that you may notice when analyzing the vehicle. In some instances, the driver of the vehicle may only notice the check engine light, and that the car does not have any other apparent symptoms of an issue.

In other vehicles, the engine may run poorly, stall, misfire, or become difficult to start. Another common symptom of a P0303 trouble code is poor gas mileage. If you notice any or all of these symptoms with the vehicle, there is a chance that it could be that you have a cylinder 3 misfire issue.


There are a few different ways that a mechanic can diagnose a cylinder 3 misfiring problem:

  • The mechanic can connect their scan tool to check for any current, pending, or history codes with the vehicle.
  • Afterward, they can note that freeze frame data for when they take the vehicle for a test drive.
  • Then, all of the codes will be cleared from the OBD2 while the mechanic takes the vehicle for a test drive to confirm any issues that may verify a P0303 trouble code.
  • Following that, the mechanic should make a full visual inspection to look for any broken components, wear and tear, leaks, and/or damaged wiring that could be causing the problem or the code to appear.
  • Then, the mechanic will use an OBD2 scan tool to check the misfire counter for cylinder 3, during operation.

Common mistakes

If these diagnosis steps above are not followed diligently, there is going to be room for error and mistakes with diagnosing and fixing the cylinder 3 misfiring issue. The most common mistakes involve overlooking fuel issues or a leaking air intake as the primary cause of the misfire. Even though the spark plugs themselves are the most common cause of this error code, they are not the only thing that could cause cylinder 3 to misfire.

How serious is this?

A P0303 trouble code can cause a few noticeable drivability problems, including a lack of engine power or that the engine is running poorly, in general. In either of these scenarios, as P0303 trouble code should prevent the driver from driving the car to a safe location where it can either be towed or repaired.  

What repairs can fix the code?

The most common fixes for a P0303 trouble code are:

  • Replacing the spark plugs for all cylinders.
  • Replacing the coil pack, cap and rotor, or spark plug wiring.
  • Repairing the intake air leaks.
  • Repairing any fuel issues.
  • Fixing any mechanical engine issues.

Related codes

None listed.


If you have any questions about this trouble code or others, it’s best to speak with an experienced mechanic or automotive professional. Feel free to contact our experts today, purchase one of our favorite scanner or repair products, or continue reading to learn more.

P0303 Code – What Does It Mean & How To Fix It