P0301

What P0301 means

The computer watches how smoothly each cylinder fires by tracking small changes in crankshaft speed. Cylinder 1 is skipping its combustion event, or firing weak, often enough that the computer flagged it. The code names the cylinder having the problem. It does not tell you why that cylinder is misfiring, and it is not naming a specific broken part.

Is it safe to drive

Drive it carefully and get it looked at soon. If the check engine light is flashing rather than steady, that means the misfire is bad enough to send raw unburned fuel into the exhaust, and that fuel can overheat and destroy the catalytic converter within minutes of driving. A flashing light means stop driving and get it towed or diagnosed right away. A steady light means the misfire is intermittent or milder. You can usually drive it in for diagnosis, but expect rough idle, hesitation, or a loss of power, and expect worse fuel economy the longer it goes unaddressed.

What commonly causes it

Most common first. A worn or fouled spark plug in cylinder 1, or a failing ignition coil, especially on engines with one coil per cylinder. After that, a bad plug wire or coil boot on engines that still use them. A vacuum leak near that cylinder's intake runner will also cause a lean misfire. Low fuel pressure or a clogged fuel injector on cylinder 1 is less common but does happen. On older or high mileage engines, low compression from a worn valve or a head gasket issue can cause the same code, and no amount of new spark plugs will fix that. Which of these is likely depends a lot on the engine. Some V6 and V8 engines have their coils buried under intake plumbing that takes real time to remove, which affects both diagnosis time and labor cost.

Diagnosis and rough cost

A proper diagnosis starts with pulling the actual freeze frame data and checking for other stored or pending codes, since a P0301 alongside a lean code or another cylinder's misfire code points somewhere different than P0301 by itself. From there it usually means swapping the coil or plug from cylinder 1 to another cylinder to see if the misfire follows the part, checking spark and fuel delivery, and sometimes a compression or leak-down test if the easy stuff checks out clean. A spark plug and coil replacement job is often in the range of a couple hundred dollars including diagnosis, but if it turns out to be a fuel injector, a vacuum leak in a hard to reach spot, or a compression problem, the cost goes up from there. We won't know which it is until it's actually tested. Auto Star does check engine light diagnostics and can tell you what's actually wrong before any parts get ordered.

Generic OBD-II guidance — manufacturer-specific codes and causes vary by make, so always confirm against your vehicle. A code identifies a system or condition; it does not, on its own, prove which part has failed.