P0301
PowertrainCylinder 1 Misfire Detected
Cylinder 1 is misfiring, fuel isn't igniting properly in that specific cylinder.
ⓘ Information only. This page provides general educational information about fault code P0301. 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 P0301 mean?
P0301 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 1 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
- • Loss of power, sometimes accompanied by a slight vibration through the steering or pedals
- • Engine warning light, flashing if the misfire is severe
- • Increased fuel consumption
- • Possible smell of unburned petrol
Possible causes
Causes commonly associated with P0301, 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 plug in cylinder 1
- 2. Faulty ignition coil for cylinder 1
- 3. Blocked or failing fuel injector in cylinder 1
- 4. Localised vacuum leak near cylinder 1's intake port
- 5. Low compression in cylinder 1 (burnt valve, head gasket, worn rings)
- 6. Damaged HT lead (on engines that still use them)
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. Inspect cylinder 1's spark plug, fouling, wear, or damage often visible
- 2. Swap the cylinder 1 coil with a coil from a healthy cylinder; if the misfire moves to the new cylinder, the coil is the fault
- 3. Swap the injector similarly to test
- 4. Compression test cylinder 1 against the others
- 5. Cylinder leak-down test if compression is low
Common questions about P0301
Where is cylinder 1? +
Cylinder numbering varies by engine. On most inline 4-cylinder engines it's the cylinder closest to the timing belt or chain. On V-engines it can vary by manufacturer. Check a reputable source for your specific engine before replacing parts.
Should I just replace all spark plugs and coils? +
If the plugs are at or near their service interval, replacing the full set is reasonable. Replacing all coils as a precaution is not, coils don't typically fail in groups, and you may waste money.
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 →