P0302

What P0302 means

The computer tracks how smoothly the crankshaft spins. When cylinder 2 fires late, weak, or not at all, the crank speed dips for an instant and the computer logs it as a misfire on that cylinder. The code does not tell you why it misfired. It just tells you where.

Is it safe to drive

This is one to take seriously. A single occasional misfire probably will not hurt anything right away. But if the check engine light is flashing, not just on steady, stop driving the car. A flashing light means the misfire is bad enough that unburned fuel is being dumped into the exhaust, and that fuel can overheat and destroy the catalytic converter within minutes of driving. That repair costs a lot more than the misfire itself. If the light is steady, it is safer to keep driving short term, but get it looked at soon. Watch for a rough idle, a hesitation or stumble under acceleration, and a smell of raw fuel from the tailpipe.

Common causes, most likely first

On most gas engines, a worn spark plug or a failing ignition coil for that cylinder is the most common cause. Some engines use one coil per cylinder, others use a coil pack shared across two or more, which changes what gets replaced. After that, a bad fuel injector on cylinder 2, or a wiring or connector problem at the coil or injector, shows up often. A vacuum leak near that cylinder's intake runner can cause the same symptom, and it is easy to blame the coil when the real problem is unmetered air getting in. Low compression from a worn cylinder, a leaking valve, or a burned valve is less common but does happen, especially on higher mileage engines, and no amount of parts swapping fixes that. Carbon buildup on intake valves is more common on direct-injection engines and can cause a misfire that looks electrical but isn't.

What diagnosis involves and rough cost

The plug for cylinder 2 usually gets pulled and checked first, since it tells you a lot for very little labor. A common next step is swapping the coil from cylinder 2 with a known-good cylinder to see if the misfire follows the coil or stays put, which points to coil versus something downstream. If plugs and coil check out, we look at injector performance, check for vacuum leaks, and if needed run a compression or leak-down test on that cylinder. A plug and coil job on one cylinder is usually a fairly small repair. If it turns out to be an injector, wiring, or a compression problem, the cost goes up, and with a compression issue it can go up a lot. We won't know which of those it is until the plug and coil are checked, so we don't like quoting a number before that step.

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.