There’s an exhaustive list (literally hundreds)of reasons why a vehicle’s check engine light may come on, but here’s a short list of common reasons:
Mass Air Flow (MAF) sensor.
System Running Too Lean. An oxygen sensor detected a lean condition (too much oxygen in the exhaust).
System Running Too Rich: The oxygen sensor detected a rich condition (or a too-high fuel to oxygen ratio).
Cylinder Misfire: Random or multiple misfire in your engine.
Insufficient EGR (Exhaust Gas Recirculation) Flow
Catalyst System Efficiency below Threshold : The oxygen sensor after the catalytic converter is detecting that the converter is not working as efficiently as it should be (according to specs).