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P0306 Code: What Does Cylinder 6 Misfire Detected Mean And 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.


P0306 code is defined as cylinder 6 misfire detected. The majority of cars are powered by an engine with four or six cylinders. And many trucks will have an engine with six to eight cylinders. In engines with six or more, the P0306 code may appear. It will specifically apply to cylinder 6, thus the term cylinder 6 misfire.

A misfire will occur when the sequence in the engine fails. The engine may skip a process in its combustion cycle and cause the engine to buck.


Code P0306 is a generic OBD2 code. It means the engine control module has detected misfires in engine cylinder 6.

Burning fuel in an efficient manner is vital to engine operation. The combustion of fuel is needed in order to produce energy to power the engine. If there is a fuel delivery problem or an insufficient amount of fuel being burned in a cylinder, a misfire can occur.


There are a few reasons why the P0306 code may appear. Here are some causes for why you may get the cylinder 6 misfire.

  1. One common cause for a misfire is related to the spark plug. Cylinder 6 may have cracks or fouling in the insulation. This can result in the spark plug not firing in the cylinder and causing a misfire.
  1. Issues with the spark plugs or plug boots may also cause a cylinder 6 misfire. Due to age, those parts in cylinder 6  may leak ignition spark to the ground.
  1. Cracked insulation or an open circuit can cause problems with the ignition coil. If the cylinder 6 ignition coil stops firing, that may cause misfires.
  1. The valve cover can also leak oil. The oil may leak into spark plug holes. This can short the ignition for cylinder 6.
  1. Engines with defective valves or rings can result in low compression problems in cylinder 6.


When an engine misfires, there are a number of symptoms you will encounter with the vehicle.

To start, the Check Engine Light will turn on. The code will be kept in the engine control module’s memory. And in the event of a cylinder 6 misfire, the Check Engine Light will also flash.

A vehicle that is dealing with P0306 engine misfires may buck. This will typically happen during acceleration or while idle. The engine misfiring will feel rough or unstable.

You may also experience diminished engine performance. The lack of engine power may affect transmission shifting. It can happen during acceleration when there is an active cylinder 6 misfire.


In order to verify the problem, scan the freeze frame data’s documents and codes. Here’s a great one we use daily. After, clear the ETC and engine codes. Check and see if the code returns by taking the car for a road test.

Take the cylinder number 6 plug wire or ignition coil out. Look on the outside of the coil and plug boot to check for evidence of spark tracking. Also check the valve cover, as there may be oil contamination from any leaking.

Remove the spark plug from cylinder 6 to carefully inspect it. If necessary, the spark plug may need to be replaced.

Finally, if there are no issues with ignition, check the engine cylinder compression for problems.

Also Read: How Long Can I Drive With a Misfiring Cylinder?

Common mistakes

There are some common mistakes people encounter when dealing with code P0306.

One common mistake is not checking to see if there is any correlation between the coil and cylinder. You can check this by switching the coil to a different cylinder. If the misfire follows the coil to the other cylinder, it indicates that you have a bad coil.

Something that is often overlooked is not checking for loose electrical connectors. Disconnected or broken vacuum hoses can often go unnoticed.

Another mistake would be to not isolate each part. Switch each part to a different cylinder. This will help isolate and identify the failed part.

How serious is this?

A P0306 code can cause damage to the engine and catalytic converter. A cylinder 6 misfire causes the engine to use more fuel, run rough and even hesitate on acceleration. Due to these things, P0306 is classified as severe.

If you get a P0306 code, it should be checked and fixed immediately. Driving a vehicle with a cylinder 6 misfire can cause significant damage to the engine.

What repairs can fix the code?

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In the case of getting the misfiring P0306 trouble code, there are a few things you can do. First, you can replace all the spark plugs if misfiring was caused by a worn-out plug. Or if you are able to identify which one was causing the issue, replace the faulty spark plug.

Another action that will fix P0306 code is to replace the valve cover gasket if it is leaking. Then, replace the plugs, wire plugs and coil if they have issues.

The ECM for a bad circuit may also need to be replaced. The circuit helps power the coil or fuel injector, so it needs to be changed if it is connected to any misfiring problems.

Related codes

The P0300 code is commonly associated with P0306.


The P0306 code will appear when you have a severe problem related to cylinder 6 misfire. It can cause consequential damage to your vehicle’s engine and should be fixed as soon as possible.

P0306 Code: What Does Cylinder 6 Misfire Detected Mean And How To Fix It