Ignition and misfire
P0301Cylinder 1 misfire detected
Cylinder 1 Misfire Detected
Stop driving or get it looked at now
Generic OBD-II code
Ignition/Combustion System (Misfire Monitor)
What this part does
The engine control module monitors crankshaft speed fluctuations to detect a cylinder that is not firing or burning fuel completely; the underlying cause is usually ignition, fuel delivery, or mechanical (compression/valve-train).
What the computer is measuring
The crankshaft position sensor watches how fast the crankshaft is turning, many times per revolution. Each cylinder that fires gives the crankshaft a small kick and the sensor sees it as a brief acceleration. A cylinder that does not fire leaves a gap in that rhythm.
Because the computer also knows where in the firing order the engine is at any moment, it can tie a missing kick to a specific cylinder. When the misses on one cylinder cross the threshold, it sets that cylinder’s code. P0301 means cylinder number one, counted by the manufacturer’s own numbering rather than by where it sits in the engine bay. On a transverse V6, cylinder one is often not the one nearest you, so check the numbering for your engine before you pull anything.
A single cylinder code is genuinely good news compared with P0300, because it narrows the problem to the parts belonging to that one cylinder: its coil, its plug, its injector and its compression. That is a short list, and three of the four can be tested by moving a part to a different cylinder and seeing whether the fault moves with it. Nothing else in diagnostics is quite that conclusive for quite that little effort.
A flashing light means the misfire is dumping raw fuel into the catalytic converter, which will destroy it in a short distance. That is a stop driving instruction.
What you will notice
- Flashing check engine light while it is misfiring, which means stop driving.
- The engine shakes at idle, often enough to feel through the seat.
- Loss of power and hesitation under acceleration.
- A smell of unburnt fuel from the exhaust.
Likely causes, most common first
Ordered by how often each one actually turns out to be the problem, not alphabetically and not by part price.
A failed ignition coil on that cylinder
On a coil on plug engine this is the most common single answer, and the easiest to prove.
A worn, fouled or cracked spark plug
Second most common. Check the gap and read the deposits before throwing it away, because they tell you what caused it.
A faulty or clogged fuel injector on cylinder 1
Less common than ignition parts but entirely possible, especially on a high mileage direct injection engine.
Low compression in cylinder 1
A burnt valve, a worn ring or a head gasket leak. The expensive answer, and the reason the swap test below is worth doing before ordering parts.
A wiring or connector fault at the coil or injector
Chafed insulation or a corroded pin produces an intermittent misfire that follows the cylinder rather than the part.
What to check, in order
Swap the ignition coil from cylinder 1 with the coil from another cylinder, clear the codes and drive it.
If the misfire moves to the cylinder you moved the coil to, the coil is the fault and you are finished. If it stays on cylinder 1, the coil is fine.
Swap the spark plug the same way if the coil test came back clean.
A misfire that follows the plug is the plug. A misfire that stays put rules out both ignition parts.
Swap the injector, or at minimum listen to it against the others with a long screwdriver or a stethoscope.
A dead or noticeably different injector explains it. All injectors ticking evenly moves the search to compression.
Run a compression test on cylinder 1 and compare it against the others.
A cylinder well below its neighbours confirms a mechanical fault and ends the parts swapping.
Where this one turns up most
- Coil on plug engines past about eighty thousand miles, where the original coils start failing one at a time.
Codes that often show up alongside it
What a DriveDecode adapter can read
A DriveDecode adapter reads engine and emissions systems: the powertrain and emissions codes the OBD-II standard requires on every US vehicle it covers. It does not read ABS, airbag (SRS), TPMS or transmission-specific manufacturer codes. Those need make-specific decoding that generic OBD-II hardware cannot do.
Reading P0301 on your own car
DriveDecode pulls P0301 straight off the vehicle along with the freeze frame the computer stored when it set: the coolant temperature, engine load and speed at that exact moment. That context is what separates a fault that happens on a cold start from one that happens under load, and it is the first thing the list above asks you to narrow down.
Last reviewed 2026-09-05. Definition sourced from the published standard.