P0300: Random/Multiple Cylinder Misfire Detected

P0300 means the engine computer has detected misfires across several cylinders without being able to pin them to one specific cylinder, so it flags the whole engine rather than a single cylinder. The most common trigger is worn or fouled spark plugs that no longer spark reliably, and a full set costs 40 to 150 EUR fitted. A steady light is a warning, but a flashing light means raw fuel is reaching the catalytic converter, so stop driving.

P0300 is a misfire-related diagnostic trouble code classified as high severity. When your vehicle's ECU detects this condition, it stores P0300 and illuminates the check engine light.

If your vehicle has triggered P0300, you may notice one or more of these symptoms:

• Check engine light flashing during the misfire or staying steadily on
• Rough idle, shaking, or noticeable engine vibration at a stop
• Hesitation or stumbling when you press the accelerator
• Loss of power, especially under load or going uphill
• Increased fuel consumption and harder cold starts
• Strong raw fuel smell from the exhaust

Here are the most common causes of P0300, ranked by how likely they are to be the culprit:

No - address this immediately. Driving with active misfires can damage the catalytic converter within minutes and may cause loss of power at dangerous moments. Pull over safely and address immediately.

Follow these steps to pinpoint the root cause of P0300:

1. Scan for companion codes (P0301 to P0312). If a cylinder-specific code is also stored, start with that cylinder before treating P0300 as a whole-engine fault
2. Inspect the spark plugs for wear, oil or carbon fouling, and a worn electrode gap. Replace the full set if they are over 50,000 km old or if several look fouled
3. Test the ignition coils, swapping one coil to a different cylinder to see if the misfire follows it, or measuring resistance with a multimeter against spec
4. Smoke-test the intake for vacuum leaks, or spray carb cleaner around the intake manifold gasket and hoses and listen for an idle change
5. Check fuel pressure with a gauge. It should hold steady at the maker's spec, typically around 40 to 60 PSI on port-injection engines, and not drop under load
6. Inspect the EGR valve for sticking and check intake valves for carbon on direct-injection engines, then run a compression or leak-down test if everything else checks out

Repair costs for P0300 vary depending on the root cause and your vehicle. Here are typical estimates:

P0300 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0300 or indicate related issues: