Decoding Your Check Engine Light

A steady check engine light means the car's computer has logged a fault that isn't an immediate danger to drive with, but shouldn't be ignored for long. A flashing check engine light means stop as soon as it's safe, a flashing light usually signals an active engine misfire that can damage your catalytic converter within minutes of continued driving.

The light itself doesn't tell you what's wrong, it tells the car's computer to store a diagnostic trouble code, things like P0300 (random misfire) or P0420 (catalyst efficiency below threshold). Any auto parts store can read that code for free, but the code is a starting point for diagnosis, not a finished diagnosis.

Common, low-urgency triggers include a loose gas cap, and the light will often clear itself after a few drive cycles once it's tightened. Common, higher-urgency triggers include oxygen sensor failures, ignition coil problems, and mass airflow sensor faults, all of which hurt fuel economy the longer they're left unaddressed.

When you take the car in, share the exact code, not just 'the light is on'. A shop that diagnoses from the code plus a proper inspection will usually save you from paying for parts swapped on a guess.