Short trips are OK if the light is steady and the engine runs smoothly, but stop driving if the light flashes or the miss worsens, since an unburned charge can overheat and destroy the catalytic converter. P0314 means the powertrain control module detected a misfire coming from a single cylinder but could not work out which cylinder it was. It is a member of the misfire family alongside the general code P0300 and the cylinder-specific codes P0301 through P0308, but with the cylinder left unidentified.
What P0314 means
The module never watches combustion directly. It infers a misfire by measuring tiny changes in crankshaft speed: every good power stroke gives the crankshaft a small acceleration, and when a cylinder fails to fire the crankshaft briefly slows more than expected during that cylinder's stroke. To turn that speed dip into a cylinder number, the module has to combine crankshaft position with the camshaft (cylinder-identification) signal so it knows exactly which cylinder was on its power stroke. P0314 sets when the speed-variation math is confident that one cylinder is misfiring, yet the cylinder-identification logic cannot reliably pin the miss to a specific cylinder. That usually happens at low speed or idle where the signal is noisy, or when a crank-to-cam correlation problem, a marginal position sensor, a damaged reluctor ring, or an incomplete adaptive relearn corrupts the per-cylinder mapping. The end result is a real single-cylinder misfire with the identity of the offending cylinder missing.
Symptoms
- Rough idle with a noticeable shake or vibration that is worst at a stop and under light load
- Occasional hesitation, stumble, or a brief dead-spot when accelerating
- Check-engine light on, and in severe cases a flashing light while the miss is active
- Reduced power and a generally rougher, less responsive engine than normal
- Slightly worse fuel economy and a raw-fuel smell from the exhaust as unburned charge passes through
Common causes
- A weak or failing ignition coil or coil-on-plug on one cylinder — the most common root of any single-cylinder misfire
- A worn, fouled, cracked, or wrong-gap spark plug on one cylinder
- A clogged, leaking, or electrically failing fuel injector on one cylinder
- Low compression in one cylinder from a burned or leaking valve, worn rings, or a valvetrain fault
- A crankshaft or camshaft position sensor fault, or a crank-to-cam correlation problem, that prevents the module from identifying which cylinder is missing
- A damaged or contaminated crankshaft reluctor (tone) ring, or an adaptive misfire relearn that has not completed
- A localized vacuum leak, or damaged wiring and corroded connectors on one cylinder's coil or injector circuit
Severity & driving advice
Severity: Moderate — A single-cylinder misfire dumps raw fuel into the catalytic converter; a flashing light means damage is happening now, so stop and diagnose it.
Can I drive? Short trips are OK if the light is steady and the engine runs smoothly, but stop driving if the light flashes or the miss worsens, since an unburned charge can overheat and destroy the catalytic converter.
Diagnostic approach
- Read all codes and the freeze-frame first — Retrieve every stored and pending code with the freeze-frame data. If a crankshaft or camshaft position sensor code (for example P0335, P0340, or a P0016/P0017 correlation code) is present alongside P0314, fix that first — a bad sync signal is a common reason the module cannot name the misfiring cylinder. Note the rpm, load, and coolant temperature captured when P0314 set, since a cold-only miss leans toward fuel or a fouled plug while a load-dependent miss leans toward ignition or compression.
- Watch the per-cylinder misfire counters — View the scan tool's individual misfire counts for every cylinder. With P0314 the counts are often smeared across cylinders or bounce around because the module could not isolate the miss, but a cylinder that still shows more counts than its neighbors is a strong lead. If one cylinder stands out you can proceed as you would for the matching P0301 through P0308 code.
- Run a cylinder-balance or relative-compression test — Because the module cannot tell you which cylinder is weak, prove it yourself. A cylinder-balance test that briefly cuts each injector, a relative-compression test read from starter current, or a manual power-balance test will reveal the cylinder that contributes the least. This is the single most useful step for turning an unidentified misfire into a specific cylinder.
- Swap ignition and fuel parts one cylinder at a time — Once the balance test points to a suspect cylinder, move its coil-on-plug and spark plug to an adjacent cylinder, clear the code, and re-run. If the miss follows the moved part, that coil or plug is the fault; if it stays put, focus on that cylinder's injector, wiring, or mechanical condition. Check the injector for a click, verify its resistance is near the factory value (roughly 12 ohms for a typical port injector), and confirm clean power and drive circuits.
- Test compression on the suspect cylinder — If a good coil, plug, and injector do not cure it, test the weak cylinder mechanically with a compression or leak-down test. A healthy cylinder should read within about 15 to 25 percent of the strongest cylinder; low, leaking-down compression points to a burned valve, worn rings, or a bent pushrod. Also look for a localized vacuum leak that leans out one cylinder before condemning internal parts.
- Verify the crank and cam signals and reluctor ring — If no single cylinder is clearly weak, the fault may be in the identification system rather than combustion. Scope the crankshaft and camshaft position signals for dropouts, check the crank-to-cam correlation, and inspect the crankshaft reluctor ring for damaged or contaminated teeth. On engines that require it, perform the crankshaft variation (misfire) relearn so the module can map cylinders accurately again.
FAQ
How is P0314 different from P0300 and codes like P0301?
P0300 means a random or multiple-cylinder misfire the module could not isolate to one cylinder, while P0301 through P0308 each name a specific misfiring cylinder. P0314 sits in between: the module is confident that just one cylinder is misfiring, but it could not identify which one. You diagnose it like a numbered misfire code, except you have to find the guilty cylinder yourself with a balance or compression test.
Why can't the computer tell which cylinder is misfiring?
To name a cylinder the module has to combine crankshaft speed with the camshaft sync signal so it knows which cylinder was on its power stroke. At idle or low speed the signal is noisy, and a weak crank or cam sensor, a crank-to-cam correlation fault, a damaged reluctor ring, or an incomplete misfire relearn can corrupt that mapping. When the identification math is unreliable the module logs the miss as unidentified rather than guessing a cylinder number.
Can I drive with a P0314 code?
Only briefly, and only if the check-engine light is steady and the engine still runs reasonably smoothly. A single-cylinder misfire sends unburned fuel into the exhaust, which overheats and can ruin the catalytic converter over time. If the light is flashing, the misfire is severe enough to damage the converter right now, so stop driving and repair it before you add a costly converter to the bill.
How do I find the misfiring cylinder when the code won't say?
Use a cylinder-balance test that briefly cuts each injector, a relative-compression test read from starter current, or a manual power-balance test to see which cylinder contributes the least. The weak cylinder is your target. From there, swap its coil and plug to a neighbor to confirm ignition, then test the injector and compression to pin down the exact fault.