For the first time, CarMD analysts reported a three-way tie for the most commonly diagnosed check-engine-light repair. "Replace ignition coil(s) and spark plug(s)" and "replace oxygen sensor" each accounted for 5.81% of repairs in 2018. U.S. vehicle owners also saw a 6.5% year-over-year increase in the average cost to repair check engine light issues, with costs up across all four U.S. regions.

The automotive diagnostics data and business solutions provider included the findings in its latest CarMD Vehicle Health Index, an annual report designed to provide an overview of information related to check engine-related car repairs, costs, and trends. Analysts included parts and component rankings this year for the first time.

"Several factors impact the type and cost of repairs, including vehicle age, driving conditions, upkeep and how often a driver addresses a dashboard warning light, which can snowball from a single faulty spark plug into the need for additional repairs if ignored," said Ieon Chen, CEO of CarMD. "By monitoring industry trends, we hope to educate drivers about the importance of repair and maintenance. Likewise, as our data reports an increase or decrease in a particular repair, automotive service professionals can adjust their customer communication and parts inventory accordingly."

Rounding out the five most common problems found to trigger the check engine light included the ignition coil and spark plug, O2 sensor, the catalytic converter, a loose or damaged fuel cap, and ignition coil without spark plug replacement. There was a slight increase in ignition coil issues, while slightly fewer mass air flow sensor, oxygen sensor and EVAP purge control valve replacements in 2018.

Analysts found the average cost to repair a check engine problem in the U.S. in 2018 was $381, including parts ($224) and labor ($157), representing an 11% increase in labor and 3.5% uptick in parts costs. Repair costs were up across all regions of the U.S., with the West seeing the largest increase (8%) and Midwest seeing the smallest (1%).

Vehicle owners in the West paid the most for check engine-related car repairs ($387) — nearly 6% more than drivers in the Midwest, who paid the least ($366). The most common repair in the West, Midwest and Northeast was "replace oxygen sensor(s)" while it was "replace ignition coil(s) and spark plug(s)" in the South.