The check engine light is the most misunderstood warning indicator on the dashboard.

The check engine light (CEL) is the most misunderstood warning indicator on the dashboard. When their vehicle’s CEL comes on, many drivers don’t know what to do. Here’s what you need to know: When the CEL is on, it means the Engine Control Unit (ECU) “computer” senses a problem that could or is affecting your vehicles’ emission control system. Too many drivers ignore the CEL hoping it will magically turn off by itself. Not addressing a CEL, even for a relatively minor fix, can lead to costly repairs.

What Is the Check Engine Light (and Symbol)?

Although known as the International Check Engine Symbol, the CEL can be a yellow, amber or orange engine-shaped warning indicator on the instrument cluster. It can be labeled “Check Engine,” “Service Engine Soon,” “Check Powertrain,” or simply “Check.” It can also have no label at all or only a label without the engine-shaped warning light.

Why Does the Check Engine Light Turn On?

When the CEL is on, it means an engine sensor (or sensors) is sending abnormal data to the computer. The problem can be a failed or failing mechanical component or one of many sensors — including the sensor sending the suspicious data itself. The computer needs accurate data to control fuel delivery, spark timing and automatic transmission shifting. If there are no noticeable drivability problems, you can drive with the CEL illuminated, but have your vehicle checked out as soon as possible. Besides turning on the CEL, the computer stores a “trouble code” in its memory that helps identify the source of the problem.