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For most people, if there is a problem with their car, the only thing they feel they can do is take it to the mechanic. Most people simply do not have the mechanical understanding and technical skill to diagnose a vehicle. If you have the right tool, however, you can read the error codes your vehicle sends. This is what mechanics do to learn what the problem is. So, if you get the OBD-II scanner error code P0305 problem, you can know that the fifth cylinder is not firing correctly. The error code does not, however, tell you why the fifth cylinder is not firing. If you want to save a little money and do not mind getting your hands dirty, you can take on the issue of figuring out what is wrong with your car’s cylinders. AutoZone will be with you every step of the way.

The Meaning of the Error

The first step is to go in-depth about what does the code P0305 mean? You should have a basic understanding of how the cylinders work and what they do before you take on the task of fixing the issue. The cylinders are the part of the engine that generates power. A mixture of fuel and air is injected into the cylinders. Then, a spark ignites this mixture and the resulting combustion pushes the cylinder down. This is where the power comes from. If a cylinder is not firing, it means this combustion is not happening and no power is being generated.

There are many things that can cause a cylinder not to fire, such as:

  • A faulty spark system
  • A faulty manifold
  • A mechanical failure of a valve or vent
  • A vacuum leak
  • A clogged EGR port

Symptoms To Watch for

If a cylinder if not firing, you will almost certainly be able to tell something is wrong with your vehicle. The engine will likely have a very choppy and rough feel to it. Additionally, the performance and fuel economy will be diminished. You may also notice a strange scent to the exhaust. Of course, the check engine light should turn on and possibly flash as well. If you do not notice any of these symptoms, that will tell you a great deal about the nature of the issue.

The Danger of Ignoring the Error

This is one of the more serious issues a vehicle may have. You should never ignore a misfiring cylinder. For the short term, the cylinder misfiring itself will likely not cause any further damage. Although it is not good for the cylinder to misfire for long periods of time. More importantly, whatever is the cause of this issue will likely cause very serious damage to the engine or catalytic converter. Problems that may arise are likely to be incredibly serious and very expensive to fix.

Possible Solutions

So how do I fix trouble code P0305? If your car is not exhibiting any symptoms, the issue is likely a faulty sensor that incorrectly detects a misfiring cylinder. Check the wiring and the sensor for damage. If you do experience the symptoms, you should first examine the spark system. A misfiring cylinder is almost always caused by the spark not being produced properly. If there is nothing wrong with the ignition coils, spark plugs, or spark plug wires, you should next examine the components surrounding the cylinder, starting with the manifold. Use a diagram to identify which of the cylinders is the number five cylinder, and look for cracks, dents, or other damage on any parts in the area. Assuming it is not an electrical or computer issue, one of these components must be the issue. If you cannot identify it, then you will need to let a mechanic take a look.

Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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