CarMD: Top 5 Reasons Your Check Engine Light Is On

CarMD: Top 5 Reasons Your Check Engine Light Is On

If one thing in life is certain, it's that at some point your check engine light will come on.  When it does, we caution you not to ignore it because if you do, it could end up being a costly repair. So what are some of the reasons your check engine light might come on? For answers we turn to the 2022 CarMD Vehicle Health Index, an annual overview of check engine light-related car repair costs and trends. With new car inventory still sparse and gas prices skyrocketing to record highs, CarMD says it provides data to vehicle owners about commonly diagnosed car problems, related costs and ways to extend vehicle life.

“The Check Engine Light is designed to come on when a vehicle’s computer sees a problem that impacts emission issues, which means if you are driving with a check engine light on – even if it seems like your vehicle is running great –you are not getting as good of fuel economy as you could be getting, you are hurting the environment and potentially doing more harm to your car or truck,” said David Rich, CarMD technical director. ”  We encourage car owners and the automotive aftermarket to reference the CarMD Vehicle Health Index to monitor check engine light repair trends, which can help inform repair diagnostics, parts purchasing and lead to extended vehicle life.”

Top 5 Check Engine Light Causes


The 2021 CarMD Vehicle Health Index lists the top five most common check engine light-related repairs along with the average cost to make that repair, including parts and labor.  Each of these issues will keep a vehicle from passing its state emissions test and will negatively impact fuel economy if ignored:

  1. Replace catalytic converter(s) with new OE catalytic converter(s), $1,355
  2. Replace oxygen sensor(s), $243
  3. Replace ignition coil(s) and spark plug(s), $387
  4. Replace mass air flow sensor, $319
  5. Tighten or replace fuel cap, (free to tighten and $25 on average to replace)

Other findings as shared in the CarMD press release include:

  • Car Repair Costs Up Amid Aging Vehicle Population.

    • In 2021 car repair costs were up 3.6% overall, totaling just under $393 on average as the average vehicle age jumps to 12.1 years old and cars start to outlive their parts.
    • Repair costs were up in all four regions of the U.S. in calendar year 2021.  Drivers in the South and Northeast saw the biggest spike – both up 3.7%.
    • Labor costs ($143.35) were down half a percent. CarMD partially attributes this to more DIYers doing their own repairs and competition among auto repair shops.
    • As projected by CarMD last year, parts costs ($249.22) were up 6%. Factors that played a role in this parts cost increase include supply chain issues coupled with an uptick in more expensive car parts failing as consumers hold onto their cars and trucks longer than ever before due to lack of new car inventory.
  • Vehicle Age Impacts Check Engine Light Problems.
    • CarMD says it found that model year 2007 vehicles were most likely to need a check engine light-related repair in the past year, with brand new (still under warranty) 2021 cars and trucks least likely to have an issue. Model year 2005-2008 cars and trucks were most likely to need a costly catalytic converter.
  • Why is the Catalytic Converter Repair So Expensive?
    • Catalytic converters contain precious metals – palladium, rhodium, and platinum – which make them a valuable commodity for thieves. The good news is that catalytic converters do not typically fail unless a more affordable repair like replacing an oxygen sensor is ignored for too long, or the vehicle is up there in age, essentially outlasting its parts.
  • Don’t Panic! The Check Engine Light Might Be Caused by a Loose Gas Cap.
    •  One of the five most diagnosed check engine light repairs is a loose, damaged or missing gas cap, which is free to tighten and roughly $25 to replace. Model year 2015, 2016, 2018 and 2019 vehicles were most likely to have a gas cap-related problem, which is data that can be useful to automotive aftermarket parts retailers for inventory forecasting.

CarMD says its 2022 Index statistically analyzes more than 17 million failures and recommended repairs for vehicles in the U.S., over the past calendar year.  If you want to check out the full Vehicle Health Index report as well as historical reports, they are available here.  

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