P0300 Code: Random/Multiple Cylinder Misfire Detected
The engine computer has detected misfires happening across multiple cylinders rather than one specific cylinder — the engine is not firing cleanly on all cylinders.
What this means for driving
A misfire fault deserves prompt attention. The main vehicle risk is that unburned fuel from misfiring cylinders can overheat and damage the catalytic converter, which turns a moderate repair into an expensive one. If the engine is running very roughly, has lost significant power, or the check-engine light is flashing, that is the situation to stop driving and arrange a tow rather than continue.
When in doubt, have a mechanic assess it promptly. If any of the red-flag symptoms below are present, stop driving and arrange a tow rather than risking it.
Important: This page is general information only — not professional mechanical advice and not a diagnosis for your specific vehicle. Fault causes and severity vary by make, model, year, and condition. A qualified mechanic should confirm any diagnosis before you make driving decisions or authorize repairs.
Red-flag symptoms: stop and get help
- Check-engine light flashing
- Severe shaking, bucking, or major loss of power
- Strong fuel smell from the exhaust
- Engine stalling repeatedly
Symptoms of P0300
- Rough idle or engine shaking
- Hesitation or stumbling on acceleration
- Loss of power
- Poor fuel economy
- Check-engine light on or flashing
- Hard starting
Most likely causes, ranked
- Worn or fouled spark plugs
- Failing ignition coil(s)
- Vacuum leak letting unmetered air into the engine
- Fuel delivery problem — weak pump, clogged filter, or dirty injectors
- Low compression in one or more cylinders
- Faulty sensor (mass airflow, crankshaft, or camshaft position)
How a mechanic diagnoses it
- Spark plugs inspected first — wear, fouling, or damage often tells the story.
- Ignition coils tested, sometimes by swapping a coil to another cylinder to see if the misfire follows it.
- Fuel pressure checked and vacuum lines inspected for leaks.
- Compression test if plugs, coils, and fuel all check out.
Likely fixes
- Replace spark plugs (DIY)
- Replace faulty ignition coil
- Repair vacuum leak
- Fuel injector cleaning or replacement
- Fuel pump replacement
Repair costs vary by vehicle, region and shop. Get a quote from a local mechanic.
Which cylinder?
If your scanner also shows a cylinder-specific code, it points to where the misfire is happening:
| Code | Cylinder |
|---|---|
| P0301 | Cylinder 1 |
| P0302 | Cylinder 2 |
| P0303 | Cylinder 3 |
| P0304 | Cylinder 4 |
| P0305 | Cylinder 5 |
| P0306 | Cylinder 6 |
Related codes
- P0301: Cylinder 1 Misfire Detected
- P0302: Cylinder 2 Misfire Detected
- P0303: Cylinder 3 Misfire Detected
- P0304: Cylinder 4 Misfire Detected
- P0171: System Too Lean (Bank 1)
CheckMyCarCode content is general information only and is not a substitute for professional diagnosis. Trouble-code meanings are standardized for generic (P0xxx) codes, but causes, severity, and repairs vary by vehicle. If your car shows a red-flag symptom, stop driving and get professional help.