P0300
Random/Multiple Cylinder Misfire Detected
- Severity
- High
- Driving
- Short journeys only
The engine is misfiring, but not on one identifiable cylinder - the control module is seeing it randomly or across several at once. Because it is not isolated to a single cylinder, the cause is usually something shared: fuel supply, a vacuum leak, ignition timing, or low compression across the engine rather than one bad part.
Possible causes
- CommonVacuum leak letting unmetered air into the intake
- CommonLow or uneven fuel pressure - weak pump or clogged filter
- CommonWorn spark plugs across the whole engine
- PossibleFaulty mass airflow sensor giving the module a wrong air reading
- PossibleEGR valve stuck open, diluting the mixture
- RareLow compression from worn timing chain or belt
What you might notice
- Engine shakes or stumbles, worst at idle
- Loss of power under acceleration
- Check engine light on, sometimes flashing
- Higher fuel consumption
- Rough or unstable idle
What to check, in order
- Listen for a hiss around the intake with the engine idling - vacuum leaks are the most common cause of a random misfire.
- Check the spark plugs. If they have not been replaced within the service interval, replace them as a set before chasing anything else.
- Look at fuel trim on the live data screen. Strongly positive trim points at a vacuum leak or weak fuel delivery.
- Check for other stored codes first. A MAF or EGR code alongside this one usually names the real cause.
- If the check engine light is FLASHING, stop driving. A flashing light means the misfire is severe enough to damage the catalytic converter.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Ignition system or misfire
P0300P0301P0302P0303P0304P0305P0306P0307P0308P0309P0310P0311P0312P0313P0314P0315P0316P0317P0318P0319P0320P0321P0322P0323P0324P0325P0326P0327P0328P0329P0330P0331P0332P0333P0334P0335P0336P0337P0338P0339P0340P0341P0342P0343P0344P0345P0346P0347P0348P0349P0350P0351P0352P0353P0354P0355P0356P0357P0358P0359P0360P0361P0362P0363P0364P0365P0366P0367P0368P0369P0370P0371P0372P0373P0374P0375P0376P0377P0378P0379P0380P0381P0382P0383P0384P0385P0386P0387P0388P0389P0390P0391P0392P0393P0394