Why Is My Check Engine Light On but My Car Runs Fine? Some problems are initially very subtle. The vehicle may be communicating that there‘s a problem before the driver can detect it. Some problems ...

The check-engine light is a signal that the onboard diagnostics system (or OBD II) has detected a malfunction in the vehicle's emissions, ignition or fuel systems.

Consumer Reports explains what the check engine light means and what to do when you see it: how to tell if your car has a loose gas cap—or a serious engine problem.