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CarMD Vehicle Health Index: Ignition Coils, Spark Plugs, O2 Sensors Tied For Most Commonly Diagnosed Check Engine Repair

CarMD’s 2019 Vehicle Health Index also found that car repair costs were up across all U.S. regions in 2018.


CarMD, provider of automotive diagnostic data and business solutions, has released its 2019 CarMD Vehicle Health Index (VHI) report. This annual VHI report provides an overview of information related to check engine-related car repairs, costs and trends.

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The report found that in 2018 – for the first time since CarMD has reported these rankings – there was a tie in the no. 1 most commonly diagnosed check engine light repair with “replace ignition coil(s) and spark plug(s)” and “replace oxygen sensor” each accounting for 5.81% of repairs. This past year, 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.

“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 after ignition coil and spark plug, and O2 sensor were 3) catalytic converter, 4) loose or damaged fuel cap and 5) ignition coil (without sparkplug 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. Spark plugs and ignition coils work together to help the engine start and stay running. Faulty spark plugs can trigger ignition coil failure, which is why they are often replaced simultaneously. High under hood temperatures and age can also cause them to fail.


CarMD found that 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 only seeing a 1% increase. 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.

The 2019 CarMD Vehicle Health Index analyzed repairs needed on more than 7 million in-use vehicles reported to and validated by CarMD’s network from Jan. 1, 2018, to Dec. 31, 2018. The full Index, including the 10 most common check engine-related repairs, 10-year history of U.S. car repair costs, list of most common repairs by region, and 10 least/most expensive repairs is available at:

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