P0301

What P0301 means

The engine computer watches how smoothly each cylinder fires by tracking small changes in crankshaft speed. When cylinder 1 isn't contributing power the way it should, on one firing or repeatedly, the computer logs P0301. It's telling you cylinder 1 specifically is misfiring. It is not telling you why. That part takes some digging.

Is it safe to drive

Say so plainly: keep driving on a steady misfire and you risk real damage. A misfire dumps unburned fuel into the exhaust, and that fuel can overheat and destroy the catalytic converter, which is a much more expensive part than whatever caused the misfire in the first place. If the check engine light is flashing rather than just on steady, that's the car telling you the misfire is active right now — get off the road and have it looked at soon, not in a week. Watch for rough idle, a shudder under load, a smell of unburned fuel, or a noticeable loss of power. If none of that is happening and the light is steady, it's still worth getting in soon, but you're not stranded.

Common causes, most likely first

Spark plugs and the ignition coil for that cylinder are the usual suspects and the cheapest to rule out. On engines with one coil per cylinder (common on newer cars), a bad coil on cylinder 1 alone is a very common cause of a single-cylinder code. After that: a leaking fuel injector or clogged injector on that cylinder, a vacuum leak pulling in unmetered air near that cylinder, or worn valve springs or low compression from a mechanical issue inside the cylinder itself — carbon buildup, a burnt valve, or in older or high-mileage engines, a compression problem that no ignition part will fix. Which of these is likely depends on the engine — some engines are known for coil packs failing, others for injector trouble, and mileage matters too. We wouldn't guess without looking.

What diagnosis involves and rough cost

Diagnosis usually starts with pulling stored codes and freeze-frame data, then swapping the spark plug and coil from cylinder 1 to another cylinder to see if the misfire follows the part or stays put. That alone often points at ignition versus something else. If it's not obviously ignition, a compression or leak-down test on that cylinder tells us whether we're dealing with something mechanical inside the engine, which is a different, bigger job than swapping a coil.

Cost varies a lot depending on what's actually wrong. A plug and coil job is a modest repair. A leaking injector costs more. A compression problem inside the cylinder is a real repair bill, and we'd walk you through what we found and what the options are before doing anything. We don't recommend replacing parts on a guess — diagnosis first, then a straight answer about what it'll take.