25 Most Common Reasons for a Check Engine Light

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 When a vehicle’s check engine light turns on, many Americans ignore it while hoping it is not a significant problem. While minor issues often trigger a check engine light, serious issues often do so as well, and failing to address the problem can lead to costly repair bills. More than 10% of vehicles on the road currently have their check engine light on.

Consultancy and automotive information provider CarMD tracks vehicle service and ownership trends. 24/7 Wall St. reviewed the 25 most common check engine light repairs as listed in CarMD’s 2017 Vehicle Health Index report.

The top 25 repairs account for 62% of all check engine repairs in the United States. Replacing a faulty oxygen sensor — a sensor used to optimize a vehicle’s fuel-to-air mixture to increase gas mileage and reduce emissions — is the most common cause for a check engine light. With over 400,000 repairs nationwide, oxygen sensor replacements account for 8% of all check engine light repairs.

Click here to see the most common check engine light repairs.

Relatively old vehicles are the most likely to have a check engine light on. Vehicles between model years 2004 and 2006 accounted for 30% of all cars that had their check engine light on in 2016. Owners of vehicles of this age can expect a lower likelihood of a check engine light if they have been consistent with regular maintenance and responded to small repairs quickly in the past.

The average cost to address a check engine signal was $398 in 2016. The cheapest repair of any common issue was a warning of a loose fuel cap, which only cost vehicle owners about $17 to repair. However, a catalytic converter replacement cost owners nearly $1,200, the most expensive repair on this list.

Nationwide, catalytic converter replacements cost Americans $429.4 million in 2016, at least three times the amount of any other repair. In total, the 25 repairs on this list cost Americans over $1.2 billion in 2016.

To determine the most common check engine light repairs, 24/7 Wall St. reviewed the 2017 Vehicle Health Index report from automotive diagnostics information provider CarMD. Each check engine light trigger as a share of all repairs, as well the average repair cost for each, also came from this report. Total nationwide 2016 recommended repairs and 2016 total cost were calculated using the share of 2016 repairs and the total repairs analyzed by CarMD in 2016. CarMD recorded a total of 5,345,588 repairs. It is important to note that while this total is a statistically valid sample, totals tend to fluctuate considerably between years.

These are the 25 most common check engine light repairs.