A check engine light doesn’t tell you exactly what’s wrong. It tells you that your vehicle has detected a problem. For most drivers, the next questions are: What’s likely causing it? How serious is it? And what could it cost to fix?
Those are questions CarMD has spent years helping drivers answer. The 2026 CarMD Vehicle Health Index analyzed more than 39 million recommended repairs from U.S. vehicles during 2025, providing insight into the problems most commonly associated with check engine light-related repairs and what those repairs cost.
One thing the data makes clear: check engine light problems can vary widely, and some seemingly smaller problems can contribute to more expensive repairs if left unresolved.
The Most Common Repair Is Also the Most Expensive
Catalytic converter replacement ranked as the most common check engine light-related repair for the second year in a row. At an average cost of $1,511, it was also the most expensive repair among the Top 10.
What makes catalytic converter replacement especially noteworthy is that the converter may not always be where the problem started. Unresolved problems such as engine misfires or faulty oxygen sensors can contribute to catalytic converter damage.
Oxygen sensor replacement, for example, ranked second at an average cost of $287. A failing oxygen sensor may be associated with poor fuel economy or rough idling, although sometimes the check engine light is the only obvious sign.
The lesson for drivers isn’t to assume one problem will inevitably lead to another. It’s much simpler: find out what triggered your check engine light rather than hoping it goes away.
Misfires Are Another Important Theme in the Data
Several of the most common repairs involve components that can contribute to engine misfires or symptoms such as rough idling, hard starts, poor acceleration and reduced performance.
Among the Top 10 were:
- Ignition coils and spark plugs: $480
- Ignition coil: $256
- Fuel injectors: $572
- Spark plugs: $299
These repairs aren’t interchangeable, and similar symptoms can have different causes. A diagnostic trouble code is an important starting point, but it doesn’t necessarily tell you which part needs to be replaced.
A Check Engine Light Doesn’t Automatically Mean a Huge Repair Bill
Seeing that little warning light illuminate can make it easy to assume an expensive repair is coming. CarMD data shows why you shouldn’t jump to conclusions. The least expensive repair among the national Top 10 was replacing an EVAP canister purge control valve, at an average cost of $172. At the other end of the list was the $1,511 catalytic converter replacement.
That’s a wide range, and another reason to understand what’s actually happening with your vehicle before making assumptions about the repair or cost.
The 10 Most Common Check Engine Light-Related Repairs
The ABS wheel speed sensor and spark plugs were new to the national Top 10, another reminder that repair patterns can change over time.
Across all of the 2026 CarMD Vehicle Health Index data, the average cost to address a check engine light-related problem reached $554 in 2025, up 33% from 2024. That doesn’t mean your check engine light will result in a $554 repair. The figure is an average across millions of recommended repairs, and your vehicle still needs its own diagnosis.
Your Check Engine Light Is On. What Now?
National data can tell us which problems are common, but the information that matters most is what’s happening with your vehicle.
Start by finding out what caused the warning light to come on. A diagnostic trouble code can provide an important clue, but additional diagnosis may be needed to identify the cause and appropriate repair.
CarMD Connect can help take some of the mystery out of that process. If you receive a compatible diagnostic report, scan its QR code in the free CarMD Connect app to get additional information about the problem, including problem severity, repair guidance and cost information. You can also use AskCarMD, the app’s AI Auto Expert, to ask questions about dashboard warning lights and vehicle problems.
The Takeaway: Turn the Warning Into Useful Information
CarMD analyzes millions of recommended repairs to identify trends in the problems vehicles encounter and what those repairs can cost. But when your check engine light comes on, the national averages are just the starting point. Understanding your vehicle’s problem, how serious it may be and what to do next can help you make a more informed repair decision.