Check Engine Light Comes On and Off in Your Car? What it Means

We’re back today with another quick tip from car repair pro Scotty Kilmer. Today’s video has nothing to do with actual repairs, but is something each of us has almost certainly encountered as we’ve driven at some point in our lives: the dreaded Check Engine light.

Not only does Kilmer break down what causes the light to come on, he addresses a phenomenon that I know personally has puzzled me at different points throughout my adult life; having the Check Engine light come on, then go back off at some point down the road, figuratively speaking. However, after hearing Scotty’s explanation, it makes a lot more sense now, so I hope this video brings you guys some clarity on this issue as well.

Basically, what Scotty shares is while you’re driving, your car is constantly running checks on all of it’s systems to make sure everything is in good working order. He flips through a manual that shows literally hundreds of potential trouble codes, each one representative of a system, function or component that the onboard computer checks constantly. If for any reason, any one of those systems, functions or components return a signal that is out of parameter for so many cycles of the testing, the Check Engine light will illuminate. However, that isn’t just a one way switch. The onboard diagnostics continue their constant checking, and if the signals return to their normal parameters for so many cycles, the light will go back off.

A perfect example, which Scotty uses in this video, is getting a tankful of subpar quality gas. This can cause detonation, or knock, that will throw a code just about every time it occurs. However, if your next fill-up is back to regular quality gasoline, the knock should clear up and the light should go back out. So don’t freak out just because the light comes, on, unless it’s blinking, in which case you may have a major issue that needs to be addressed promptly.