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P0305: Cylinder 5 Misfire Detected

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What is P0305?

Code P0305 is defined as “Cylinder 5 Misfire Detected.

This diagnostic trouble code (DTC) indicates that your Powertrain Control Module (PCM) has counted several misfire events on cylinder 5 of your engine.

The cylinders in your vehicle’s engine are responsible for generating power. The fuel injector injects fuel into these cylinders, which is then combusted by a spark from spark plugs. The resulting force from the fuel combustion is what drives the crankshaft and your wheels. 

When these cylinders work together, the crankshaft’s RPM stays consistent. However, when repeated misfires occur on any cylinder, it leads to a loss of engine power. 

Your vehicle’s PCM continually tracks the crankshaft’s RPM via the crankshaft position sensor signals. When it detects fluctuations in these signals due to a cylinder 5 misfire, it registers the P0305 code and activates the Check Engine Light.

Common symptoms

One of the most common signs for the P0305 code is an illuminated or flashing Check Engine Light. A flashing Check Engine Light is more severe as it can indicate damage to the catalytic converter. 

Here are the other common misfire code symptoms you should look for: 

  • The engine hesitates or jerks when you accelerate
  • Lack of engine power 
  • Rough idle
  • Poor fuel economy
  • Fuel smell from the exhaust

Can I still drive?

A cylinder 5 misfire is a serious error code. You should stop driving the vehicle immediately and get the code diagnosed ASAP.

P0305 code can cause your engine to run rich, which means it’ll consume more fuel and could damage your catalytic converter. Fixing or replacing a catalytic converter is a pretty expensive repair too. 

A misfiring cylinder may also cause your engine to run rough or hesitate during acceleration, resulting in decreased engine power and fuel economy.

P0305 causes

A P0305 cylinder misfire can occur for a multitude of reasons, right from a faulty spark plug and fuel system errors to internal engine damage. 

That said, the most common reason for a cylinder 5 misfire is a worn-out spark plug, ignition coil, or coil pack. 

The other common P0305 code  misfire reasons include: 

  • Faulty spark plug wire 
  • Vacuum leak 
  • Faulty or clogged fuel injector 
  • Low fuel pressure 
  • Contaminated or old fuel 
  • A defective crankshaft position sensor
  • Engine timing off
  • Faulty timing belt
  • Leaking head gasket 
  • Low engine compression 
  • Defective PCM

Note: If your PCM registers other engine codes along with P0305, the causes may differ from those listed above.

Diagnosis

Whether you own a Honda Motor Company vehicle or a Mazda, a cylinder number 5 misfire can occur due to various factors. So, a thorough and accurate diagnosis is necessary. 

Here’s how a certified technician will diagnose code P0305: 

  • They’ll start by using an OBD-II scan tool to read the trouble code and the freeze frame data stored by your vehicle’s PCM. They’ll also check if any other error code is present and fix it first. 
  • Next, they’ll look for any loose wiring around the spark plug or ignition coil and the cylinder 5 harness. They’ll look for a loose engine ground wire as well. 
  • They’ll inspect the vacuum hoses for leaks and ensure that all hoses are firmly connected. 
  • Your mechanic will move on to inspecting the condition of the spark plug, spark plug wire, and harness. If the spark plug or its wire is worn out, they’ll replace it. Ideally, your mechanic will replace all the spark plugs together. When going for a new plug, long-lasting iridium plugs are a good option if your engine is compatible.
  • If your vehicle uses individual coil packs, they’ll swap the cylinder 5 coil pack with a different cylinder. If the misfire shifts to a different cylinder, the misfire is probably due to a faulty ignition coil. 
  • If the spark plug and its wire or the ignition coil are not at fault, they’ll check if your engine is getting sufficient fuel. They’ll inspect the fuel pump, fuel filter, and fuel pressure regulator for the source of low fuel pressure. They’ll also check the fuel injector and the fuel injector wiring for any damage. 
  • Your mechanic will also check if you’re using the right fuel grade specified for your vehicle. 
  • If the fuel system is working fine, they’ll perform a leakdown and compression test on your engine. This is to check for any mechanical problems causing the cylinder misfire. Sometimes a misaligned timing belt or a worn-out head gasket can lead to a cylinder misfire.

Possible repairs for P0305 & Costs

Although the P0305 error code is a generic powertrain code, its fixes depend on your car’s make and model. 

Trouble code repairs usually begin with an hour of diagnosis that may cost you $75-$150. Once the mechanic identifies the root cause, they’ll suggest the required repairs. 

Replacing the spark plugs or ignition coil is the most common and cheapest repair. So, a mechanic will always start there before moving on to other repairs. 

Here are some of the repair or replacement cost estimates (including labor charges) for code P0305: 

  • Spark plugs: $66-$250
  • Spark plug wire: $180-$240
  • Ignition coil: $230-$640 
  • Vacuum leak: $100-$200
  • Fuel pressure regulator: $200-$400
  • Fuel injector: $1500-$1900
  • Fuel pump: $1300-$1700

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