Seeing your vehicle's check-engine light come on can throw a wrench in your travel plans. It can also feel a little scary: Does it mean your ride is headed for the scrapyard? Or is there a simple fix?

It’s something no driver wants to see: a check engine light glowing on the dashboard. You know something’s wrong with your car—but what, exactly? That’s where an OBD2 code reader comes in handy. These ...