Check engine light on? What it means and what to do

The check engine light is your car's way of saying its computer has noticed something outside normal limits. It can mean almost anything, from a loose gas cap to a problem that can damage the engine. Here's how to tell the difference.

Steady or flashing?

A steady light means the car has logged a fault. It isn't usually an emergency, but it shouldn't be ignored either. Get it checked soon.

A flashing light usually means the engine is misfiring badly enough to damage the catalytic converter. Ease off, avoid hard acceleration and get the car checked as soon as you can. If the car is running rough or shaking, it's safest not to keep driving.

Check the easy thing first

A loose or worn gas cap is a common cause. Tighten it until it clicks. The light won't go off right away; it can take several drives before the car rechecks and clears it.

A code isn't a diagnosis

When the light comes on, the car stores a trouble code. Reading the code tells you which system flagged a problem, not what failed. A code for a lean condition, for example, could come from a vacuum leak, a fuel delivery problem or a faulty sensor. Replacing parts based on the code alone can cost money without fixing anything.

Proper diagnosis means reading the codes and the live data, testing the suspect parts, and confirming the cause before anything gets replaced.

When to bring it in

• The light is flashing
• The light is steady and stays on after you've checked the gas cap
• The car runs rough, hesitates, stalls or uses more fuel than usual
• You smell fuel, or the temperature gauge is climbing