P0300: Random/multiple cylinder misfire detected
One or more cylinders did not burn their fuel properly. Unburnt fuel can overheat the catalytic converter.
Updated
What P0300 means
A misfire is a combustion stroke in which the fuel in a cylinder doesn’t burn properly. The engine computer notices it as a tiny dip in the crankshaft’s speed, and counts how often it happens.
P0300 means misfires were seen in more than one cylinder, or the computer couldn’t tell which one. Misfires in several cylinders at once point to something they share, such as a vacuum leak or the fuel supply.
P0301 to P0312: a misfire in one cylinder
These codes name the cylinder that misfired: the last two digits are its number. The meaning, causes and advice are the same as for P0300, but the search is narrower. Where cylinder 1 is depends on the engine; the service information for your car shows the numbering.
On engines with an ignition coil per cylinder, a common check is to swap the coil with the one of a neighbouring cylinder. If the misfire code moves to that cylinder, the coil is at fault. The same check works for spark plugs.
P0301: Cylinder 1 misfire detected
P0302: Cylinder 2 misfire detected
P0303: Cylinder 3 misfire detected
P0304: Cylinder 4 misfire detected
P0305: Cylinder 5 misfire detected
P0306: Cylinder 6 misfire detected
P0307: Cylinder 7 misfire detected
P0308: Cylinder 8 misfire detected
P0309: Cylinder 9 misfire detected
P0310: Cylinder 10 misfire detected
P0311: Cylinder 11 misfire detected
P0312: Cylinder 12 misfire detected
Can I keep driving?
Drive gently
Avoid hard driving and have it checked soon. It can damage the engine or catalytic converter. If the check engine light flashes, stop when it’s safe to do so.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
Misfires let unburnt fuel into the exhaust, where it burns inside the catalytic converter and can overheat it. A check engine light that flashes means the misfires are bad enough to do that: stop when it’s safe to do so.
A pending code means the car has seen the misfire but not confirmed it yet. It’s still worth looking into before the converter suffers.
Symptoms
- The engine shakes or runs unevenly, most noticeably at idle or when pulling away.
- Hesitation or loss of power when accelerating.
- A check engine light that flashes while the misfire is severe. With milder misfires it stays on steadily.
Common causes
- Worn spark plug or failing ignition coil. A common cause on petrol engines. A weak coil or plug may only misfire under load, when accelerating.
- Faulty injector. A clogged or leaking injector gives its cylinder the wrong amount of fuel.
- Vacuum leak. Unmeasured air makes the mixture too lean to burn reliably, often in several cylinders at once.
- Low compression. For example from worn valves or piston rings, or a leaking head gasket. A compression test shows it.
Typical fixes
- Note which cylinder codes are stored, and any fuel mixture codes (P0171, P0174) stored with them.
- Check the spark plugs and ignition coils of the cylinders named, starting with the coil swap described above.
- Check for vacuum leaks, especially when several cylinders misfire or lean codes are stored too.
- Have the injectors and the compression tested if the ignition parts are fine.
- Clear the codes after the repair. The car checks for misfires all the time while the engine runs, so a misfire that’s still there soon shows up again.
Questions
Can I drive with a misfire code?
Gently, and not far. The app’s advice is to avoid hard driving and have it checked soon, because misfires can damage the catalytic converter. If the check engine light flashes, stop when it’s safe to do so.
What does the number in P0301 to P0312 mean?
The last two digits are the cylinder number: P0301 is cylinder 1, P0304 is cylinder 4. Where cylinder 1 is depends on the engine, so check the service information for your car.
Why do misfire codes come with P0420?
Misfires that go on for a while can damage the catalytic converter, which can later set P0420. Fix the misfire first: a new converter would be damaged the same way.