What Does Your Check Engine Light Mean?

Your check engine light (CEL), also known as the malfunction indicator lamp (MIL), illuminates if one of your car's computers or sensors is indicating a problem. Little things, like a loose gas cap or a faulty oxygen sensor, can set off the check engine light, but it can also be an indication of a far more serious problem, such as worn-out timing equipment or a bad catalytic converter. Whatever the cause may be, it’s crucial to visit an auto parts store, repair facility, or dealer to diagnose the issue and make any necessary repairs.

CELs most commonly come in an orange or amber color, with either an icon in the shape of an engine block or words like "check engine." A steady check engine light is usually an indication of a serious but not urgent problem. If the check engine light starts flashing (or turns red), it means something is wrong under the hood and the car needs to be shut down and towed to a repair facility. For example, a misfire can overheat the emissions system and cause a fire, and a timing issue can potentially cause catastrophic damage. In this article, we'll cover the top reasons why a check engine light comes on and determine a course of action for this scenario.

Jump to:
Most common reasons why the check engine light comes on
How to decipher the check engine light with a code reader
Possible false flags from a check engine code
Don't ignore that light
How to turn off the check engine light
Brief history of the check engine light
FAQs

Most common reasons why the check engine light comes on

Vehicle telematics company CarMD publishes its Vehicle Health Index annually, compiling the 10 most common check engine codes and their estimated cost of repair. According to CarMD's 2026 Vehicle Health Index, the top 10 repairs resulting from a check engine light are:

^{(Source: CarMD Vehicle Health Index 2026)}

According to CarMD's most recent data, labor rates are up, as are replacement part costs. That's bad news for car owners, as the average cost to repair a check engine light–related issue is up to an all-time high of $554, a huge increase from the previous year's $415. Some reasons for the big price jump include greater mechanical complexity requiring more labor and more expensive replacement parts due to material shortages and, potentially, tariff-related charges.

CarMD's most recent report suggested that customers were hanging onto their cars longer than ever, and the average age of the vehicles in the study was 12.8 years old, another all-time high. As a result, aging consumables such as catalytic converters were the No. 1 cause of an illuminated check engine light. That said, a check engine light can illuminate on a newer car as well, so it's important to pay attention to your vehicle's built-in warning system. 

If you're driving an older car, it may be tempting to trade up to a more recent vehicle with fewer problems. Edmunds can help decide if fixing your old car or getting a new one is a wise decision, as well as whether to buy brand-new or go for a used car instead. 

How to decipher the check engine light with a code reader

There are literally thousands of reasons why a check engine light might illuminate. A local mechanic or dealership service department can easily diagnose the problem for the cost of an hour of labor (or even for free), but there's another slightly more convenient way to figure out what's wrong with your car. All you need is a code reader and Edmunds' list of diagnostic trouble codes (DTCs) and their causes.

Some auto parts stores will loan code readers for customers to use in the parking lot, and a decent code reader could be a wise purchase for a DIY home mechanic. These readers connect to your car's onboard diagnostics (OBD) port and display a five-character alphanumeric code. By consulting Edmunds' list of DTCs or searching for the code on a website like Engine Light Help, you'll be able to figure out why the CEL is illuminating. 

Steve Mazor, retired chief automotive engineer for the Auto Club of Southern California, says that an inexpensive check engine code reader could be useful for car owners who aren't mechanically inclined.

"If the mechanic gives you the same information, at least you know they are going down the right road," he notes. A code reader can provide car owners with one more data point to help them talk with their mechanic and avoid costly or unnecessary auto repairs. Just keep in mind that you'll have to figure out where your car's OBD-II port is (typically somewhere in the driver's footwell) and get comfortable with plugging in and operating the code reader. It's also important to remember that many cars didn't have an OBD-II port until the 1996 model year, so if you're driving a classic, you'll need to do a little more research to figure out what's going on.

Possible false flags from a check engine code

With the code and its meaning in hand, a do-it-yourself interpretation can still be a little tricky even if you are mechanically inclined. For example, a code might suggest that a sensor has gone bad when, in reality, it could be that the wiring leading to the sensor is faulty. Diagnosing the issue means looking at everything potentially connected to the check engine light code.

It's also important to distinguish the difference between a check engine light and a service indicator. The CEL illuminates when there's a problem detected somewhere in the vehicle, while a service indicator comes on when the car needs its scheduled maintenance. Edmunds has a guide to the manufacturer-recommended maintenance intervals for almost any vehicle if you'd like to learn more.

Don't ignore that light

It's crucial to pay attention to your car's dashboard and address any warning lights as soon as possible.

"The check engine light is designed to come on when a vehicle's onboard diagnostic system sees a problem that impacts emissions or drivetrain issues," said David Rich, CarMD technical vice president. "With uncertainty about how tariffs will impact replacement part prices, it's particularly important for drivers to address their car's dashboard warning lights. Catching problems early can reduce the likelihood of a snowball effect from additional repairs."

In a recent survey of U.S. vehicle owners, CarMD found that nearly half (49%) reported having a dashboard warning light on. Of that group, 20% reported their vehicle's check engine light was on — nearly double the number from the last time CarMD conducted a similar survey. In the same survey, 22% reported having a tire pressure light on, which CarMD noted was understandable since the survey was conducted in January, when cold temperatures can cause low tire pressure. 

One of the simplest fixes for a check engine light is inspecting the gas cap. Forgetting to tighten it after a fuel stop or fastening it incorrectly can flag a problem with the car's evaporative emissions system, causing a check engine light. If the cap is loose, tighten it and drive for several miles — if that was the problem, the light should go out. Other cheap repairs could include replacing an air filter, cleaning fuel injectors, or cleaning a mass airflow sensor, which can be done by just about anyone.

What should you do if the check engine light comes on and it's steady rather than flashing? The most obvious answer is to get the vehicle checked by a mechanic, but you might be tempted to ignore it, especially if you know that a steady light is less of an immediate concern than a flashing one. Indeed, many people simply do nothing, perhaps fearing an expensive repair. Some drivers with older vehicles may want to squeeze out as many remaining miles as possible without visiting a service garage.

This isn't wise, however. For example, driving with a faulty oxygen sensor or a misfiring engine can lead to excessive fuel consumption, and besides costing you money every time you fill up, it can also lead to accelerated catalytic converter failure. Since the cost to replace a catalytic converter easily exceeds $1,000 on some popular car models, promptly addressing a check engine light is an important means of saving money in the long run. Even in the case of a loose gas cap, ignoring the problem would result in increased emissions and reduced engine performance. 

How to turn off the check engine light

Your vehicle is not likely to pass a state safety inspection with the check engine light on. This reality can be a good motivator for dealing with the problem. Ultimately, the engine and the emission control system are so interlinked that the health of the emission control system is a good indicator of the engine's overall health. Having the issue resolved by a mechanic is the best way to make your check engine light disappear

Still, some people might want to turn off the light temporarily for a number of reasons. Most code readers will allow you to turn off or reset the check engine light, which can be handy for DIYers who want to see if they've successfully repaired their cars. But unless you've read the code, deciphered its cause, and replaced or cleaned the relevant parts, this action alone does not actually address the problem. In many cases, you're only delaying the inevitable, and the light will come back on within a day or two.

Occasionally, the check engine light comes on when nothing is wrong with the car, said Mazor. It could be a temporary problem caused by a change in humidity or other factors. In such cases, the light should go off by itself after a short time.

Brief history of the check engine light

Automakers started standardizing their systems with 1996 model-year vehicles under a protocol called OBD-II, which instituted a list of diagnostic trouble codes and mandated that all cars provide a universal connector to access this information. The connector is usually located under the steering column and is relatively easy to access. Before 1996, carmakers had their own engine diagnostic systems, primarily to ensure their cars were compliant with EPA pollution control requirements. These systems were not standardized, however, and required special tools and know-how to decipher the cause of a check engine light. 

FAQs

Is it safe to drive your car with the check engine light on?
It depends on the severity of the issue. If it's a minor issue, such as a loose gas cap, it should be safe to drive. If you notice a difference in the performance of the vehicle, it could indicate a more serious problem, and it's best to err on the side of caution. Reduce your speed and take the vehicle to a mechanic as soon as possible. If the check engine light is flashing, exercise particular caution because your car is trying to tell you that there's a major malfunction — it might be time to consider a tow truck.

Is the check engine light serious?
If the culprit is a gas cap, a check engine light isn't serious. If it's caused by temporary changes in the environment, the light should go away on its own. But if the light stays on or turns amber, there's a good chance the car is releasing excess pollutants or consuming too much fuel. That's not only bad for your gas mileage, but it's also a sign of a more serious issue that may need immediate attention. If the check engine light is flashing or if it turns red, there's almost certainly a serious issue that requires immediate expert attention.

How many miles can you drive with the check engine light on?
Since each fault code has its own level of severity, it is difficult to predict how many miles you can drive with the warning light on. The cause could be anything from a bad sensor to plug wires that need to be replaced. The safest bet is to decipher the code as soon as possible and then plan your strategy accordingly.