I'm just going to elaborate on the types of CEL and their meanings. Generally, a steady lit CEL indicates some sort of emission equipment fault. The gas cap is the easiest one to trigger this sort of CEL if you don't tighten it properly.
A flashing CEL indicates an active engine misfire, at least one cylinder is not firing properly. You'll usually feel the rough engine during this, but not necessarily on larger motors.
Typically, the CEL will go away on its own if the fault(s) that trigger the CEL are good again. This can take a few days or more, usually several full driving cycles.
I'll concur with the others, you need to get the codes read to figure out why its on. It may be one code, it may be a few. But, until then, everyone would just be guessing.