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What That Dreaded 'Check Engine' Repair Will Cost You

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The average car on the road today is almost 11 years old, and even though cars are built to last longer, all that wear and tear takes a toll.

In fact, 80 percent of vehicles are in need of service or repairs right now, but if you've been ignoring that "check engine" light on your dash, you're not alone. CarMD.com, which tracks repair trends on cars up to 10 years old, says more than 9 million U.S. drivers have ignored their car’s “check engine” light for three months or more.

Ignoring it, though, could wind up costing you a bundle down the road. The light is alerting you to a problem with the car's engine or related systems. It could be as simple as a loose gas cap that needs tightening. But a blinking check engine light indicates there's a more severe problem that is doing mechanical damage to your car and should not be ignored.

When this occurs, the best thing to do is limit your driving and have the problem diagnosed by a mechanic as soon as possible, according to CarMD, which collects repair data on 136 million vehicles based on "check engine" incidents.

Virtually all vehicles manufactured since 1996 are equipped with a "check engine" light, which is part of an on board diagnostics system that is constantly checking information from engine to transmission sensors to look for emissions-related problems. It’s found on more than 220 million vehicles in North America, and covers about 80% of the systems on most cars, light trucks, SUVs and minivans.

The most common failure is the oxygen sensor, which monitors the amount of unburned oxygen in the exhaust and tells your car’s computer when there is either too much, or not enough fuel. Getting it replaced costs less than $200. Ignore it and you'll likely see a 40 percent drop in your car's gas mileage. The same goes for the mass air flow sensor, which calculates the amount of air coming into the car and determining yhow much fuel to shoot into the engine. If it goes bad, your mileage could drop by up to 25 percent. It costs about $375 to fix, but will save you money at the pump.

Getting the "check engine" light to turn off could be as easy as replacing a spark plug. Spark plugs are responsible for igniting a car's air/fuel ratio. When they fail, they can cause an engine “misfire,” reduce your gas mileage, and ultimately ruin your car's catalytic converter. If you do it yourself, replacing a spark plug can cost under $10. Having it done by certified mechanic costs a couple hundred dollars, but can save you thousands. A damaged catalytic converter will cost $1,000 or more to fix, but is avoidable if you address small problems early.

CarMD looked at real-life repair data for one full calendar year on 2002-2012 vehicles and discovered that different brands tend to have a unique set of problems and common failures. For instance, a malfunctioning oxygen sensor accounted for about 28 percent of Mini repairs in 2012, while bad ignition control modules accounted for 26 percent of Saab repairs, according to CarMD. Subaru had a tendency to need a new catalytic converter (22%); and Scion was susceptible to loose or damaged gas caps (20%).

Full List: The Most Common Repairs For Each Car Brand

The CarMD Vehicle Health Index points out common problems by brand, which may be important to know as you consider future maintenance costs.

Repair patterns differ by make, model, year and mileage, so the best way to check on the repair history of your car is to check out CarMD’s Vehicle Health Index Scorecard feature.