Cylinder 1 Misfire Detected
In short
P0301 means the engine computer detected a misfire specifically in cylinder 1. Because it's pinned to one cylinder, the cause is almost always something on that cylinder — a worn spark plug, a failing ignition coil, a bad injector, or (less often) low compression. The quickest diagnosis is to swap parts from cylinder 1 to a neighboring cylinder and see whether the misfire moves.
Is it safe to drive with P0301?
A steady light with a mild single-cylinder misfire is usually okay for a short, gentle drive to get it fixed. A FLASHING check engine light means raw fuel is reaching the catalytic converter and can destroy it — stop driving. Even a steady misfire shouldn't be left for weeks, because it overheats and damages the cat over time.
Symptoms
- Check engine light on, sometimes flashing under load
- Rough idle and a noticeable vibration
- Hesitation or stumble on acceleration
- Slight loss of power
- Reduced fuel economy
- Occasional smell of unburnt fuel
Common causes (most → least likely)
How to diagnose it (before buying parts)
- 1 Locate cylinder 1 for your specific engine — it's not always the one nearest the front. Check the firing-order/cylinder diagram for your make.
- 2 Swap the ignition coil from cylinder 1 to an adjacent cylinder and clear the code. If the misfire follows the coil (e.g. becomes P0302), the coil is bad. If it stays on cylinder 1, the coil is fine.
- 3 Inspect the cylinder 1 spark plug — look for fouling, wide gap, cracked porcelain, or oil. Replace if questionable.
- 4 If coil and plug are good, swap the fuel injector (or do an injector balance/buzz test) to check for a clogged injector.
- 5 Use a scan tool to watch the cylinder-1 misfire counter live and check fuel trims for a nearby vacuum leak.
- 6 If ignition and fuel are ruled out, do a compression and leak-down test on cylinder 1 to check for a mechanical fault.
Repair options & cost
By manufacturer
Usually a coil or plug. Denso/NGK OEM coils and plugs are the dependable fix; aftermarket coils sometimes fail again quickly.
Coil-on-plug failure is very common. The swap test is fast and definitive on these engines.
Check the plug first on higher-mileage engines; if oil is fouling the plug, look at valve-cover gasket / spark-plug tube seals leaking oil into the well.
Coils and plugs are routine wear items and often fail one at a time. Replace in sets if several are aged; use OEM coils.
Frequently asked questions
What does cylinder 1 misfire mean?
It means cylinder 1 isn't firing cleanly on every combustion cycle. The computer monitors crankshaft speed and flags the specific cylinder that's dropping power — here, cylinder 1.
Can I just swap the coil to confirm it's bad?
Yes — that's the standard test. Move cylinder 1's coil to a neighboring cylinder, clear the code, and drive. If the misfire moves with the coil, replace the coil. If it stays on cylinder 1, the coil is fine and you look at the plug, injector, or compression.
Is P0301 expensive to fix?
Usually no. The most common fixes are a spark plug or a single ignition coil — often under $100 in parts. It only gets expensive if the cause is a fuel injector or a mechanical problem like low compression.
Why fix it quickly?
Unburnt fuel from a misfiring cylinder overheats and damages the catalytic converter. A flashing check engine light means that damage is happening now — stop driving until it's repaired.