The check engine light means the engine computer has stored a fault code. It does not say which part has failed — only which reading was out of range.
Steady or flashing
Steady means book a scan soon. Flashing means a misfire is sending unburnt fuel into the catalytic converter, which can destroy it: slow down and come in.
Try the cap first
A loose fuel cap is the most common cause. Tighten it until it clicks; the light may go out after a few days of driving.
