No. 3: Faulty ignition coil(s) and spark plugs
Average repair cost: $390.67
Up from fourth place from the year before, this accounts for 6.19% of repairs in 2015 -- nearly double from 2014, when it was 3.58% of repairs.
Because ignition coils use the current from the car battery to ignite the spark plugs, ignoring spark-plug problems can result in a faulty ignition coil (or coils). These parts also fail over time due to high under-hood temperatures.