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P0305 Error – What to Do When Your Car Engine Misfires 

  • Cars Explained
  • Celine Jerly
  • 6 minutes

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So, your Check Engine light is on, and an OBD-2 scan returns the code P0305. You might have also noticed a jerk when accelerating and a decrease in fuel economy. P0305 error is the DTC (Diagnostic Trouble Code) for a cylinder misfire in the engine – specifically cylinder 5. Find out what this means and why you need expert help to immediately fix it.  

To break it down for beginners, OBD-2 (On-Board Diagnostic) codes are a part of your car’s self-diagnostic system. When your car’s ECM (Engine Control Module) detects a malfunction, the Check Engine light turns on. But to determine what exactly is wrong, you’ll need a code reader or OBD-2 scanner. Each OBD-2 code indicates a specific issue and helps mechanics take the appropriate actions to fix it. OBD-2 codes are also referred to as Diagnostic Trouble Codes (DTC) or Check Engine Light Codes. 

In this case, P0305 is the generic OBD-2 code for “Cylinder 5 Misfire Detected.” It means that cylinder 5 in your car’s engine is malfunctioning.  

A cylinder is a chamber inside your car’s engine, where the power is generated when gasoline burns. Most engines have 4 – 8 cylinders; typically, more cylinders mean more power. However, some super (expensive) cars have engines with up to 12 cylinders (V12) or 16, like the Bugatti Chiron! 

So, what causes these cylinders to malfunction and result in a Check Engine error?  

What is cylinder five misfire or P0305 error? 

Power is generated inside an engine cylinder when fuel combustion occurs at specific times as the pistons move up and down. A misfire occurs when the ignition timing is off, usually caused by a malfunctioning fuel or ignition system or internal engine failure. If you haven’t tuned up your car in a while, worn-out spark plug coils could be the simple explanation.  

There is no crankshaft acceleration from the power stroke when a cylinder misfire occurs. This indicates that the cylinder is not producing power. When the crankshaft sensor in the engine detects this error in cylinder 5, the P0305 error code is triggered and set in ECM memory.  

What are the symptoms of P0305 error? 

Loss of power with unusual vibrations is one of the most common signs of an engine misfire. Your car might also shake while idling, and the engine runs rough, sometimes with a noticeable jerk when you accelerate. You might also notice a decrease in fuel economy, as the other cylinders have to compensate for the power lost due to the misfiring cylinder. Check for fuel smell from the exhaust too.  

Once the Check Engine light turns on, the OBD-2 code is set in ECM memory. If the light flashes during a misfire, it could be a warning of catalyst damage. This means that the catalytic converter is exposed to contaminants covering the working surfaces, stopping it from treating the exhaust.  

What causes cylinder five to misfire or P0305 error? 

From a faulty spark plug to poor quality fuel, there are several causes for a cylinder 5 misfire. Once a P0305 error is detected, you’ll need expert help to figure out what’s causing it and fix it efficiently. This is a severe engine problem, and if you are not experienced enough, it’s best to take your car to the shop at once than try to repair it at home.  

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Common causes of P0305 error code cylinder 5 misfire are: 

  • Spark plug or ignition coil not firing 
  • Ignition spark leaking from spark plug wire or plug boot 
  • Oil leaking into spark plug holes from the valve cover 
  • Leaking head gasket or a vacuum leak 
  • A malfunctioning fuel injector or low fuel pressure 
  • Faulty engine distributor 
  • Camshaft or crankshaft sensor defects 
  • Bad fuel – poor quality or contaminated 

How to fix the code P0305 error? 

You need an OBD-2 code scanner to determine the P0305 error. Once detected, the next step is to diagnose the cause and what triggered the error code. There are multiple reasons for cylinder misfire. A mechanic should ideally follow this checklist: 

a mechanic checking engine of a car

  • Scan and ensure P0305 is the only error. If other DTC codes are detected, those should be fixed first
  • Document freeze frame data 
  • Clear other DTC codes detected and check whether any error repeats 
  • Verify the misfire by road testing the car 
  • Remove the ignition plug wire or coils to check for spark tracking evidence 
  • Switch the spark plug to another cylinder to verify the misfire is due to a faulty coil or wire 
  • Check for leaking valve cover causing oil contamination 
  • Check for loose engine ground wires that cause random misfires 
  • If no ignition problems are detected, check the fuel system (fuel pressure and fuel injectors)  
  • Check cylinder compression; run an engine compression and leak down test  
  • Check for mechanical problems like leaking head gasket, broken vale spring or piston ring, and burned valves or worn-out valve guides. 
  • Check whether the timing belt jumped a tooth or if the engine is off-time
  • Look for loose electric connectors and disconnected vacuum hoses 

Usually, replacing faulty or worn-out spark plugs or leaking valve gaskets fixes the P0305 error. But the diagnosis and repair are a time and labor-intensive process. So if you do not have mechanical knowledge, it’s best not to DIY it.  

How much does it cost to fix a cylinder five misfire? 

An accurate estimate could be made only after determining what is causing the error. However, you can expect to spend around $80 – $130 to fix a code P0305 error. In severe cases, replacing fuel system parts like the pump or injectors costs as much as $1700 – $1900. Spark plug and wire replacements cost around $60 – $240, while a vacuum leak fix can be done for $100 – $200.  

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Can you drive with a cylinder five misfire? 

The P0305 error code indicates a severe engine problem. Do not drive when a misfire is active; it will cause further engine damage and increase repair costs. Not to mention the decrease in fuel economy and performance. Immediately take your car to the mechanic to avoid catalytic converter damage and ignition failure.  

Can an engine misfire fix itself? 

No, unless it is an external problem, engine misfire cannot fix itself. If you do not find the root cause of cylinder five misfires and take shortcuts, the error will return with a heavier bill from the mechanic.  

Once a P0305 code is detected for engine trouble, you ideally need a mechanic’s help to diagnose the problem. Fixing a cylinder five misfire requires at least intermediary mechanical knowledge and specialized equipment. It is not recommended for beginners; you could end up causing more damage than there is. But it does help to be aware of the problem and the ways to fix it. 

Also see: How to fix error code – P0300, P3031, P0302, P0303, P0304, P0306


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