P0300
PowertrainRandom/Multiple Cylinder Misfire Detected
Your engine is misfiring across two or more cylinders, fuel isn't burning properly somewhere in the combustion process.
ⓘ Information only. This page provides general educational information about fault code P0300. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0300 mean?
P0300 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Random/Multiple Cylinder Misfire Detected.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Rough or uneven idle, especially when stopped at lights
- • Hesitation, jerking or loss of power on acceleration
- • Engine warning light, often flashing if the misfire is severe
- • Increased fuel consumption
- • Sometimes a smell of unburned petrol from the exhaust
- • On older or higher-mileage engines, occasional backfiring
Possible causes
Causes commonly associated with P0300, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Worn or fouled spark plugs
- 2. Failing ignition coil pack or coil-on-plug unit
- 3. Faulty or clogged fuel injector
- 4. Vacuum leak (split hose, intake manifold gasket)
- 5. Low fuel pressure (failing fuel pump or blocked filter)
- 6. Carbon-fouled intake valves (common on direct-injection engines)
- 7. Crankshaft or camshaft position sensor fault
- 8. Loss of compression (head gasket, burnt valve, worn rings)
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Connect a diagnostic tool that supports live data and check the misfire counter for each cylinder. This often points straight to the affected cylinder(s)
- 2. Visually inspect spark plugs and HT leads for wear, damage or fouling
- 3. Swap a coil pack from a misfiring cylinder to a healthy one. If the misfire follows the coil, the coil is the fault
- 4. Check for vacuum leaks (carb cleaner spray test or smoke test)
- 5. Test fuel pressure against the manufacturer's specification
- 6. If all of the above are clear, perform a compression test
Common questions about P0300
Can I drive with a P0300 code? +
Whether driving is safe depends on the cause, which only an in-person diagnosis can confirm. Generally, a misfire can dump unburned fuel into the catalytic converter and may damage it over time. A flashing engine warning light is typically associated with a more severe misfire. Common professional advice in that situation is to avoid further driving and seek prompt diagnosis. Always confirm with a qualified mechanic.
Will P0300 clear itself? +
Sometimes. If the cause was a one-off (a tank of bad fuel, a moment of damp weather). More often the code returns within a few drive cycles. Generally, addressing the underlying cause is more reliable than waiting for the code to clear itself.
Does P0300 mean engine damage? +
Not on its own. P0300 reports a misfire. The cause may be as simple as a £15 spark plug. Ignored over time, it can damage the catalytic converter (an expensive repair) and, in severe cases, contribute to bore wash and ring damage.
Why does the misfire only happen sometimes? +
Intermittent misfires often track with engine load (only under acceleration), temperature (only when cold or only when hot), or moisture (only in damp weather). These patterns help identify the cause, note when it happens and tell your mechanic.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →