Check Engine Light Diagnostic

What is the Check Engine Light?

Call it the most misunderstood indicator on your dashboard: The check engine light can mean many different things, from a loose gas cap to a seriously misfiring engine.

What the Light Means

The check engine light is part of your car’s so-called onboard diagnostics system. Since the 1980s, computers increasingly have controlled and monitored vehicle performance, regulating such variables as engine speed, fuel mixture, and ignition timing. In modern cars, a computer also tells the automatic transmission when to shift.

When it finds a problem in the electronic-control system that it can’t correct, a computer turns on a yellow warning indicator labeled “check engine,” “service engine soon,” or “check powertrain.” Or the light may be nothing more than a picture of an engine, perhaps with the word “check.”