Replace oxygen sensors
Oxygen sensors remained the most common car repair, accounting for 7.1% of repairs in 2014. The O2 sensor can fail because of neglecting car repairs, internal engine leaks or burning oil, or by using gas with a higher ethanol concentration. A malfunction can cause as much as a 40% drop in fuel economy and can affect performance. The average cost of the repair decreased $2 from the prior year.
Catalytic converter troubles decreased slightly from 2013 to 2014. These parts won't fail unless there is an underlying problem, such as with a spark plug or the ignition coil. It represented 5.89% of repairs in 2014. This is the most expensive repair in the top 10, though costs increased only $3 over 2013.
Tighten loose fuel cap
A gas cap that is loose, missing or damaged can trigger the check-engine light and also allow gas to evaporate. This problem accounted for 5.4% of repairs, compared with 7.1% in 2013. CarMD said the low cost of this repair means that most mechanics are likely diagnosing this problem, but expect to spend $30 if the gas cap needs replacing.
Replace ignition coils and spark plugs
Because ignition coils use the electrical current from the car battery to ignite the spark plugs, ignoring spark plug problems can result in faulty ignition coils as well. These parts also fail over time because of high under-hood temperatures. This problem accounted for 3.58% of repairs in 2014.
Replace ignition coils
Replacing the ignition coil or coils -- some cars have more than 1 -- accounted for 3.57% of repairs in this year's study. Ignition coils can malfunction because of high under-hood temperatures and their overall age. Pay attention to problems, as ignition coil failures can cause other problems, including with the pricey catalytic converter.
Replace mass air flow sensor
A malfunctioning mass air flow sensor, or MAF, accounted for 3.54% of repairs, CarMD's latest study shows. Problems with the MAF can result in a 10% to 25% decrease in fuel economy because it measures the air coming into the engine and calculates how much fuel to inject.
Replace spark plugs and spark plug wires
Replacing spark plugs and wires accounted for 3.28% of repairs. Replacing a spark plug can cost just $10 if you do it yourself, but drivers spend $361.56 on average to have spark plugs and their wires replaced by a technician. When these items fail, they can cause the engine to misfire and gas mileage to decline. Ignoring the problem can result in permanent damage to your car's expensive catalytic converter.
Thermostat repairs are new to the top 10, representing 2.18% of repairs. A car's thermostat regulates the engine's temperature by opening and closing to regulate the flow of coolant. If the coolant isn't changed as recommended, or the car is driven in extreme temperatures or an acidic environment, corrosion can occur, causing it to fail prematurely.
Replace exhaust gas recirculation valve
Exhaust gas recirculation problems represented 1.95% of repairs in 2014. This system controls emissions and helps your car run more efficiently. Cars with an EGR problem can experience rough idling, engine hesitation and misfires. The result can be compromised performance, reduced fuel economy and problems passing emissions tests.
Replace fuel injectors
Faulty fuel injectors represented 1.75% of repairs in 2014. A fuel injector problem can be hard to diagnose; the problem can slowly build until the part fails entirely, resulting in the car not running. Fuel injectors can get clogged by not using name-brand fuel or by picking up debris in the fuel tank by running the car when the tank is repeatedly near empty.