Check Engine Light On? Here's What to Do

The check engine light is the most misunderstood light on your dash. Here's the decision guide we give our own customers.

First: steady or flashing?

Steady light: something's wrong, but it's not an emergency. Drive normally and book a diagnosis this week.

Flashing light: an active misfire is dumping raw fuel into the exhaust, which can destroy the catalytic converter in minutes — a four-figure part. Slow down, avoid hard acceleration, and get it in immediately.

Quick self-checks

Tighten the gas cap (a loose cap is a classic trigger — the light may take a few drives to clear). Note anything different: rough idle, smells, power loss, when it happens. Those details speed up diagnosis.

Why a free code read isn't a diagnosis

A code tells you what the computer noticed, not why. P0420 ("catalyst efficiency") might be a failing $40 oxygen sensor, an exhaust leak, or a genuinely dead converter. Replacing parts by code is how people spend $800 to not fix a $150 problem. Real diagnostics test the circuit and component before anything gets replaced.

Will it pass emissions?

With the light on, no — and clearing the code right before a test doesn't work, because the computer reports "not ready" until it completes its drive cycles.

Light on now? Book a diagnostic at your nearest shop — read more about how our diagnostics work.