I took my car in to the shop because the "check engine" light was on and found out this was simply due to my gas cap being loose. Why would that set off the warning light? – Louis in Duncan, B.C ...

The check engine light is your car’s way of alerting you that something's amiss — but it could be as minor as a loose gas cap, or more serious, like a faulty oxygen sensor. Repair costs for ...

Three weeks later, after I changed my oil, I noticed that the check engine light was off. Did the light burn out? No, because when I turn the key to start the car, I see it light up.

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.

Three weeks later, after I changed my oil, I noticed that the check engine light was off. Did the light burn out? No, because when I turn the key to start the car, I see it light up.

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.