Check Engine Light

What Does “Check Engine” Light Mean?

The “check engine” light is part of your car’s
Onboard Diagnostics System (OBD).

Computers increasingly control and monitor vehicle performance, regulating such variables as engine speed (RPM), fuel mixture, and ignition timing. In some cars, the computer also tells the automatic transmission when to shift. When it finds a problem in the electronic-control system that it can’t correct, the computer turns on a yellow warning indicator that’s labeled “Check Engine,” “Service Engine Soon” or “Check Powertrain.” Or the light may be nothing more than a picture of an engine. In addition to turning on the light, the computer stores a “Trouble Code” in its memory that identifies the source of the problem. The code can be read with an electronic scan tool or a diagnostic computer. Manufacturers originally used the OBD system to help technicians pinpoint and troubleshoot malfunctions in the emissions systems. Exactly what the OBD system looks for depends on the make, model and year. The original systems varied widely in their capabilities, but changed by 1996, when, under OBD II regulations, carmakers were required to install a much more sophisticated system that essentially acts like a built-in emissions testing station. The computer monitors and adjusts dozens of components and processes. In most cases, if a problem occurs, the computer will wait to see if it corrects itself before turning on the light.