OBD2 Trouble Code P030X

OBD2 Trouble Code P030X

The P030X codes are a set of codes that indicate a misfire. It is one of the most common issues that can happen to a car, and a few misfires won’t harm your engine. However, repeated issues can cause damage to other systems. It’s best to solve the issue as soon as convenient.

What Does P0301 “Cylinder X Misfire Detected” Mean?

A P030X code simply means that the car’s computer has detected a misfire. A misfire occurs when the air and fuel in the combustion chamber don’t combust or combust at the wrong time. You can read more about them here.

There are two different P030X codes you will come across.

The P0300 code means that there are multiple engine misfires in multiple cylinders. This code can be caused by a lot of different problems, so you will likely have other codes as well.

The P030(1,2,3,…) indicates a misfire on a specific cylinder. For instance, P0301 means a misfire on cylinder number 1, and a P0305 means a misfire on cylinder number 5.

How Serious Is Code P030X?

A misfire by itself isn’t likely to damage your car. The problem with misfires is that they are often a symptom of other problems, and those underlying problems may be more serious. It’s important to look out for the following symptoms that could be signs of a bigger problem.

Stop Driving

  • If the car’s performance is suffering greatly
  • You hear unusual engine noises, especially knocking or loud clunks
  • There is white smoke coming from the tailpipe

Catalytic Converter Issues

It’s important to get a misfire diagnosed and fixed as soon as possible because they sometimes pose a risk to the catalytic converter in your car. Those can be very expensive to replace. We talk about catalytic converters here if you want to know more.


  • The engine feels sluggish or loses power while accelerating
  • It’s difficult to start the car
  • You hear popping or backfiring
  • The check engine light is illuminated

The Check Engine Light

The check engine light is your car’s way of letting you know that the computer has detected a problem. It can often be your only indicator that something is wrong. If your CEL is illuminated, use an OBDII reader like one of these we recommend to scan for stored codes. If the CEL is flashing, you need to stop driving when safe because that means there may be serious engine damage.


Unfortunately, there are a lot of reasons an engine may misfire. If you are getting a misfire on a specific cylinder, it’s a little easier to diagnose since you can focus on a single area. Our page on misfires has a lot of more in-depth information if you want to explore further.

There are five areas to check first.

Spark Issue

The ignition module, coil pack, plug wires, and spark plugs are all part of your ignition system. If one part is damaged or failing, combustion may not initiate at the appropriate time, causing a misfire. Use a spark plug tester to quickly check for a faulty spark plug or wire.

Fuel Issues

If your engine is not getting sufficient fuel, then combustion won’t occur, and you will get a misfire. The most common reason for lack of fuel is a fuel pump issue, which you can test with a pressure tester like these we recommend. Usually, a fuel pressure issue will cause a generic P0300 code and not a code identifying a specific cylinder.

Vacuum Leak

A vacuum leak will cause all sorts of issues, especially if there is a leak near the intake manifold because that can mess with all sorts of systems. The EGR system and the MAP both use the manifold vacuum to operate, and they can both cause an engine to misfire if they fail. Use a smoke test to check for vacuum leaks.

Faulty Sensors

Most sensors connected to the engine’s computer can cause misfires if they fail. There are a couple of really common sensor issues. A dirty or clogged mass airflow sensor can cause fuel issues, and a faulty camshaft or crankshaft position sensor can cause misfires on multiple cylinders.

Low Compression

Low compression is a worst-case scenario because it means that internal engine components are damaged or malfunctioning. You can perform a leak-down test or a compression test to check the engine’s health.


Solving an engine misfire issue is largely a process of elimination. You start with the easiest causes to service, like the spark plugs and airflow sensors, and work your way through the list replacing components until you finally replace the one that causes the code to clear.

The following items are some tips and tricks to help you keep your sanity during the process.

  • Doing a simple service is often a good way to eliminate misfires. New spark plugs, new oil, and new filters can go a long way towards solving a lot of engine issues.
  • It is rare, but if you notice that you are getting a lot of misfire codes, but are not experiencing any symptoms, you may have a faulty computer. You will probably have to take the car to a service center to diagnose a faulty PCM/ECU.
  • If you are experiencing misfires on a specific cylinder, a good first step is to swap the coil, wire, and plug with a cylinder you know is working. Move one component at a time, and if the code changes, you have found the issue.
  • It can be beneficial to replace all associated components if you suspect one has failed. For instance, if you find a fouled spark plug, it’s good practice to replace all the plugs if you haven’t done so recently. That can prevent chasing the same problem in circles around the engine.
  • One of the most infuriating things that can happen concerning engine misfires is that the issue can go away on its own. Small, random events can sometimes cause misfires, and when the event is over, you’ll be left with a code that has no cause. If you aren’t noticing many symptoms, you can simply clear the code and see if it comes back.

Just remember to be methodical and label the parts you remove, and you’ll have it solved in no time.

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