Malfunctioning mass air flow sensor
Average repair cost: $423
A malfunctioning mass air flow sensor accounted for 3.35 percent of the repairs in 2013. Problems with the sensor can result in 10 percent to 25 percent fuel economy reduction, since it's the mass air flow sensor that measures the air in the engine and calculates how much fuel to inject. Costs are up 3 percent from 2012.