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