P0314
PowertrainSingle Cylinder Misfire (Cylinder not Specified)
One of your cylinders is misfiring, but the ECU can't pin down which one. So instead of giving you a tidy P0301 to P0304 telling you the exact cylinder, it throws this catch-all code. For you that means the diagnosis takes a bit more legwork, because you're hunting a fault the car itself can't fully locate.
ⓘ Information only. This page provides general educational information about fault code P0314. 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 P0314 mean?
P0314 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Single Cylinder Misfire (Cylinder not Specified).
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:
- • Engine warning light, sometimes flashing under acceleration when the misfire is bad
- • Lumpy, uneven idle with a noticeable shudder through the car
- • Hesitation or a flat spot when you put your foot down
- • Fuel economy drops off, often the first thing owners notice on the daily commute
- • Vibration that comes and goes, frequently worse once the engine is warmed through
- • Occasional stall under load, like pulling away from a junction
Possible causes
Causes commonly associated with P0314, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Worn or oil-fouled spark plugs, the cheapest and most common starting point, especially if they're past their service interval
- 2. Failing ignition coil or cracked HT lead breaking down under load. Coil-on-plug setups are notorious for one weak coil causing exactly this
- 3. A clogged or sticking fuel injector starving one cylinder of fuel
- 4. Vacuum leak on the intake manifold or a perished hose, leaning out one cylinder more than the rest
- 5. Crankshaft or camshaft position sensor giving the ECU patchy data, which is partly why it can't identify the cylinder
- 6. Low compression on a cylinder from worn rings, a burnt valve or a head gasket starting to let go
- 7. ECM or wiring fault, rare, but worth considering once everything else checks out
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. Pull the freeze-frame data alongside the code. The RPM, load and temperature at the moment of fault tell you whether it misfires cold, hot, at idle or under load, and that narrows the hunt straight away
- 2. Check for companion codes. A P0301 to P0312 often shows up next to P0314 and hands you the exact cylinder, so always read the full list before you start swapping parts
- 3. Inspect the spark plugs and coils. Pull each plug and look for one that's oil-soaked, sooty or has a worn gap compared to its mates. A single odd plug usually points you at the culprit
- 4. Swap a coil to a different cylinder and clear the code. If a misfire follows the coil, you've found it. This is one of the quickest tests on a coil-on-plug engine
- 5. Smoke-test or spray-test for vacuum leaks around the manifold and intake hoses if ignition checks out clean
- 6. Run a compression test as the last resort. If ignition, fuel and vacuum are all healthy and one cylinder still misfires, you're looking at a mechanical problem inside the engine
Common questions about P0314
What happens if I just keep driving on it? +
A persistent misfire dumps raw unburnt fuel into the exhaust, and that fuel ignites inside the catalytic converter and cooks the substrate. A cat is a £300 to £800 repair on most cars, far more than the spark plug or coil that probably caused the misfire. You'll also burn more fuel and the engine may drop into limp mode. If the light is flashing, that's the ECU telling you the catalyst is being actively damaged right now.
How quickly do I need to sort this? +
If the engine light is steady and the car drives more or less normally, you've got days, not weeks, to get it looked at. If the light is flashing or the misfire is bad enough to feel through the pedals, treat it as urgent and stop driving as soon as it's safe. The longer a heavy misfire runs, the more likely you are to be buying a cat as well as a coil.
Is it the part itself or just the wiring and connectors? +
On these, it's usually the part, a tired spark plug or a coil that's broken down internally. But don't rule out the connectors. Coil plugs sit in a hot, vibrating environment and the little locking clips go brittle, so a loose or corroded connector can mimic a dead coil exactly. Wiggle the harness and check the pins before you condemn a coil that might be fine.
How long does the repair usually take? +
A set of plugs is an hour or so on most engines, longer on a V6 where the back bank is buried. A single coil swap is often a 20 minute job once you've found the right one. The time sink with P0314 is the diagnosis, not the repair, because you're identifying a cylinder the car won't name for you. A compression test adds an hour or more, and if it turns up internal wear the timescale jumps to days and the bill climbs into four figures.
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 →