What Is Misfire?
A misfire is a combustion event that doesn't occur, occurs incompletely, or occurs at the wrong time in a cylinder. The engine computer counts misfires per cylinder and stores P0300-series codes when rates exceed thresholds.
In plain English
A misfire means a cylinder's air-fuel charge didn't burn properly — no spark, wrong mixture, or poor compression. The driver feels it as a stumble, shudder, or rough idle; the computer sees it through crankshaft speed fluctuations.
Misfires matter beyond drivability: unburned fuel travels into the exhaust and can overheat the catalytic converter. That's why an active misfire often flashes the check-engine light rather than glowing steadily.
Example
Related trouble codes
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