OBD-II diagnostic trouble code
P0300Caution
Random/Multiple Cylinder Misfire Detected
Your engine's computer has detected that cylinders are misfiring in a pattern that doesn't point to one specific cylinder — it's happening randomly across several of them. A misfire means one or more cylinders aren't burning fuel properly on every cycle, which wastes fuel and can damage the catalytic converter over time.
Symptoms
- Engine runs rough or shakes, especially at idle
- Noticeable loss of power or hesitation under acceleration
- Check engine light flashing (not just steady on) during the misfire
- A faint smell of unburned fuel from the exhaust
Likely causes
- Worn or fouled spark plugs — the single most common cause
- Vacuum leak letting unmetered air into the engine, leaning out multiple cylinders at once
- Fuel delivery problem — weak fuel pump or a clogged fuel filter starving several injectors
- Low or contaminated fuel, or a bad batch that's affecting the whole engine rather than one cylinder
How to diagnose it
- Pull the spark plugs and check their condition — worn, fouled, or badly gapped plugs across multiple cylinders confirm the likely cause
- Use a smoke test or spray carb cleaner around intake gaskets/hoses while the engine idles to spot a vacuum leak
- Check fuel pressure at the rail against the spec in the service manual — low pressure under load points to the fuel pump or filter
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Code names are compiled from open/standardized SAE and ISO references. Explanations, symptoms, causes and fixes are original. Covers generic (P0/C0/B0/U0) codes only — manufacturer-specific codes are planned for a future update.
Frequently asked questions
Can I drive with P0300?
You can usually keep driving with P0300, but don't put it off — the underlying cause can get worse or lead to further damage the longer it goes unaddressed. Get it diagnosed as soon as you reasonably can.
How much does it cost to fix P0300?
Typical repair costs for {code} range from roughly 60 to 600 EUR, depending on the specific cause and your car — see the fixes listed above for a breakdown.
What causes P0300?
Worn or fouled spark plugs — the single most common cause Vacuum leak letting unmetered air into the engine, leaning out multiple cylinders at once Fuel delivery problem — weak fuel pump or a clogged fuel filter starving several injectors
Reviewed by Artyom SemenovAutomotive Editor · Fact-checked by Yauheni Kapliarchuk, Editor-in-Chief