Uh-Oh. What Does That 'Check Engine' Warning Light Mean?

BOSTON (MainStreet) — Some 10% of U.S. vehicles have their "Check Engine" lights on at any given time — but half of drivers ignore the warning because they fear their cars will need expensive repairs, market watcher CarMD.com has found.

"People say: 'My car is driving fine' or 'This is just my dealer trying to stick it to me,'" CarMD's Kristin Brocoff says. "But if you ignore the problem, it's just going to snowball."

All U.S. cars built after the 1995 model year come with on-board diagnostic computers that constantly monitor some 80% of a vehicle's systems to uncover problems as soon as issues develop.

Mandated originally by the U.S. government to spot malfunctions that increase your car's emissions, many on-board computers now go beyond the official requirements and monitor a vehicle's battery, antilock brakes and other systems.

Serious issues will prompt the "Check Engine" light to illuminate on a car's dashboard — something many vehicle owners dread. After all, you'll need to take your vehicle to a repair shop or buy a special handheld device from CarMD or one of its competitors just to find out what's wrong.

Many of the roughly 650 problems that can trigger the "Check Engine" indicator also cost big bucks to repair. For instance, CarMD says a broken transmission assembly — the most-expensive problem associated with the warning light — runs about $5,474 to fix.

Fortunately, CarMD says serious problems represent only 1% of cases involving "Check Engine" lights.

The firm, which analyzed 161,000 indicator-related repairs done last year by U.S. mechanics, found that the average malfunction costs just $368 to fix.

That's good news, because your car will fail annual safety-and-emissions inspections automatically in many states if the "Check Engine" light is on. Some problems will also slash your vehicle's fuel efficiency, Brocoff adds.

Here's a look at the five most common things CarMD found triggered "Check Engine" lights last year, as well as a rundown of average repair costs: