P0303 Code: Cylinder 3 Misfire Detected

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The first question you are likely asking yourself is, “What does the code P0303 mean?” This code is a generic error message that relates to OBD-II-equipped vehicles, and it refers to issues in the powertrain.

However, the code does not necessarily refer to any specific actions that should be taken as these steps will vary based on the make and model of your vehicle. However, the code does indicate that the vehicle’s computer system has sensed an issue in at least one of the car’s cylinders.

What does The P0303 Code Mean?

The P0303 code is an OBD II Diagnostic Trouble Code (DTC) defined as “Cylinder 3 Misfire Detected.”

It is a generic trouble code that triggers your vehicle’s check engine light. It gets registered in your Powertrain Control Module when the misfire monitor detects several misfire events on Cylinder 3. 

This Cylinder 3 misfire code may often get registered along with other misfire and lean/rich condition codes.

The P0303 code means that your Powertrain Control Module (PCM) or Engine Control Module (ECM) has detected multiple misfires on cylinder number 3. The misfire monitor tracks crankshaft speed variations through the crankshaft position sensor (crankshaft sensor). Any relative loss in the crank speed during the cylinder’s power stroke counts as a misfire.

When that happens, the PCM creates a freeze frame data for the event, logs the P0303 code, and triggers your vehicle’s check engine light.

P0303 Code

What are the Symptoms of the P0303 Code?

While everything is clearer in retrospect, it still pays to understand the potential warning signs of this problem.

For example, if your engine seems to be harder to start, or if it seems to stumble or hesitate upon ignition, then it could be a sign that one of your cylinders is not acting the way that it should.

However, pinpointing the specific cylinder can be a complicated process without the assistance of the error code message.

  • Check the Engine Light flashing.
  • Rough running, hesitation, and/or jerking when accelerating.
  • In most cases, there are no adverse conditions noticed by the driver.
  • In some cases, there may be performance problems, such as dying at stop signs or rough idling, hesitation, misfires, or lack of power (especially during acceleration), and a decrease in fuel economy.

What Causes 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:

How does a mechanic diagnose the P0303 code?

There are many different systems that cause the P0303 code, so it is critical to follow all steps in the proper order:

  • The mechanic will hook up a scan tool to check for any current, history, or pending codes.
  • Next, all freeze frame data will be noted for use on the test drive.
  • Codes will all be cleared, and a test drive will be taken.
  • Now, a visual inspection will be performed looking for wear, broken components, leaks, and damaged wiring.
  • A scan tool will be used to check the misfire counter for cylinder #3 during operation.
  • Long-term fuel trims will be checked to verify if any fuel or intake issues are present.
  • In some cases, the spark plugs may be pulled and inspected.

Common P0303 Code Diagnostic Mistakes

  • Like any other diagnosis that is done, all steps must be followed to avoid mistakes that waste time and money.
  • Not properly inspecting all the parts
  • Replacing the unnecessary parts
  • Not confirming the existence of the P0303 code
  • Clearing the code without first verifying the problem
  • Replacing the spark plug or fuel injector without inspecting the wiring and connectors.

How serious is the P0303 code?

The P0303 trouble code is potentially quite serious. If your vehicle has the engine light turned on and the PCM registers this OBD-II trouble code, you should stop driving immediately.

Since your vehicle’s engine relies on the proper functioning of its cylinders, a cylinder misfire could lead to internal engine damage, which may be costly to repair.

Moreover, if the P0303 code isn’t diagnosed and resolved at the earliest, it could also lead to ignition failure, catalytic converter damage, and dangerous driving conditions.

What Repairs Can Fix the P0303 Code?

Here’re some of the possible fixes to resolve the P0303 code:

  • Replacing the spark plugs for all cylinders.
  • Replacing the burned or damaged valve
  • Repairing the fuel rail leaks
  • Replacing the bad fuel injectors for all cylinders
  • Replacing the fuel regulator
  • Replacing the bad fuel pump
  • Replacing the fuel pressure sensor
  • Replacing the spark plug wiring or coil pack.
  • Adding more fuel if needed
  • Reprograming or replacing the PCM

How Much Does It Cost To Fix A Cylinder Misfire?

P0303 can be caused by anything from old spark plugs to vacuum leaks to poor engine compression. It’s impossible to give an accurate estimate without properly diagnosing the issue first.

Once your mechanic has diagnosed the trouble code correctly, they’ll suggest a replacement or repair for fixing the misfires.

Repairing or replacing a cylinder can range from $100 to $1,000. Different causes for misfires cause different severities of damage that each cost varying amounts to repair. These damages are:

  • Slower fuel delivery issues can cost anywhere from $200 to $1,000.
  • Spark plug wires aren’t working properly and cost anywhere from $100 to $300.
  • Broken piston rings can cost anywhere from $1,500 to $3,000.
  • Broken valve springs can cost anywhere from $450 to $650.
  • Oil-fouled spark plugs can cost anywhere from $100 to $250.
  • Faulty ignition coils can cost anywhere from $150 to $250.