These Were the 5 Most Common Check Engine Light Car Repairs In 2021 According to CarMD

When a check engine light comes on, that means the vehicle’s computer detected a problem affecting the emissions controls or driveability. These problems could be minor but could still cause harm to the environment or impact the vehicle’s fuel economy. However, it’s also possible the problems could be serious and lead to expensive repairs or maintenance if not addressed. This leads to a question: What are the most common check engine light repairs?

CarMD reveals the most common check engine light repairs

A man repairing a car, likely after the check engine light came on
Car Repairs | Justin Sullivan/Getty Images

CarMD collects data on auto repairs and publishes its Vehicle Health Index report on the most common check engine light-related problems, repairs, and associated costs. Using this report, let’s look at the five most common issues in 2021, including the repair cost and frequency of occurrence. 

5. Inspect for loose fuel tank cap – tighten or replace as necessary

The fifth most common check engine light issue is a loose fuel tank cap, which CarMD reports occur 4.28% of the time. It seems trivial, but a loose gas cap will not only allow contaminants to get into the fuel system but can allow dangerous fuel vapors to escape the vehicle. These vapors are harmful to the environment and potentially cause health issues. 

The fix for this problem is to either tighten the gas cap or replace it if it has a bad seal. The average cost for this repair was $24.77.  

4. Replace mass air flow (MAF) sensor

Occupying the fourth spot on CarMD’s list of the most common check engine light car repairs is the mass air flow (MAF) sensor. The mass air flow sensor measures the volume of air flowing into the engine intake and adjusts the fuel flow to achieve the proper air-fuel ratio. When the MAF sensor malfunctions, it causes the air-fuel ratio to become too lean or too rich, causing fuel economy and driveability issues.   

The average cost for a MAF sensor repair was $319.02, which covered the part and labor. According to CarMD, this problem occurred 4.53% of the time. 

3. Replace ignition coil(s) and spark plug(s)

At number three on CarMD’s list are issues with the ignition coils and/or spark plugs, which occurred 4.92% of the time. When this problem occurs, the vehicle’s engine could run rough or misfire, leading to performance and driveability issues. 

The fix for an ignition coil or spark plug issue is to replace the faulty part or parts when the diagnostic codes indicate multiple misfires. The average cost for this car repair was $387.47, but it could be more or less depending on the number of ignition coils or spark plugs replaced.   

2. Replace oxygen sensor(s) 

Oxygen sensor issues come in at number two on CarMD’s most common check engine light car repairs. Most vehicles have two to three oxygen sensors that measure the volume of oxygen in the exhaust. This lets the engine management system know if the engine is running too rich or too lean. 

A bad oxygen sensor caused 5.58% of issues and cost an average of $242.87 for parts and labor.  

1. Replace catalytic converters 

The catalytic converter is number one on the list for both frequency and repair costs. A leaking, clogged, or stolen catalytic converter costs an average of $1,355.78 and occurred 5.78% of the time.  

A bad or missing catalytic converter can cause a range of issues, from increased pollution to poor engine performance. Catalytic converters use precious metals like platinum, palladium, or rhodium to burn off excess hydrocarbons, which is why catalytic converter theft is on the rise, as reported by the National Insurance Crime Bureau.

How CarMD sourced its data for the most common check engine light car repairs

To provide this information, CarMD maintains a database with over 17 million repairs recommended in 2021 for 1996 to 2021 model year vehicles. Their list of the top 10 most common vehicle repairs applies to more than 85% of the cars, light trucks, minivans, SUVs, and hybrids on the road in the U.S.   

Your car’s check engine light is no joke

There’s an old joke about a driver who sees their check engine light come on, so they take it to a mechanic. The mechanic pops the hood, looks, and says, “Yep, the engine is still there.” And then charges the customer $200. 

The reality is that a check engine light is no joke. The problem may be simple and inexpensive to repair, or it may be something serious. As in the case of the five most common check engine light car repairs, it’s important to get the problem checked and repaired before it becomes a bigger issue.     

To provide this information, CarMD maintains a database with over 17 million repairs recommended in 2021 for 1996 to 2021 model year vehicles. Their list of the top 10 most common vehicle repairs applies to more than 85% of the cars, light trucks, minivans, SUVs, and hybrids on the road in the U.S.   

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