Check engine light
The check-engine light means the ECU stored a fault that failed an emissions or system monitor.
A steady lamp is a stored code. A flashing lamp usually means a misfire that can overheat the catalyst, so reduce load and read the code before a long trip.
The lamp itself is not a diagnosis. Scan the code — often P0420, P0300, or P0171 — and open that page for the next checks.
A trouble code marks a condition to test. It does not by itself prove which part to replace.