Check Engine Light - What It Means and What to Do About It

When the check engine light comes on in a vehicle, it’s indicating that there is some issue with the car that should be checked out. It could be something minor, such as the gas cap not being screwed on tightly. Or it could indicate something much more serious, like a problem with the engine or transmission.

Depending on the manufacturer, the check engine light can vary in color and appearance, but they nearly always include the international symbol below indicating the vehicle needs to be checked soon.

Waiting too long to have a check engine light diagnosed can sometimes cause small issues to become large ones. This article provides tips on what this signal could mean, and even how to diagnose a check engine light at home. 

What Causes the Check Engine Light to Come On?

Every vehicle contains many sensors designed to illuminate the check engine light, signaling something is not safe or not operating properly. Many of these sensors pertain to performance and/or environmental issues. 

Some issues are insignificant and easily fixed, such as if the gas cap is not on correctly. In this case, the car is losing fuel into the atmosphere, which can be costly and detrimentally affect the environment. Tightening it will solve the problem.

But the check engine light could indicate a much more serious problem, such as faulty ignition. The problem could be minor, or it could be a risky malfunction that would not only be costly, but extremely dangerous. It is important to have a check engine light diagnosed as quickly as possible to rule out major engine trouble.

Can I Drive With the Check Engine Light On?

Yes, driving for a little while with the check engine light on should be okay. There is no need to stop in the middle of traffic or in an unsafe location. Some vehicles have check engine lights showing varying degrees of urgency. A yellow light is the least urgent, followed by orange and red. A blinking red light is the most urgent. 

If the red light is blinking, check the dashboard to see if any other warning lights or gauges appear. Certain indicators are a warning that the problem must be addressed immediately. Two of the most serious for your engine are low oil pressure, shown here:

Oil and coolant are the lifeblood of your engine.

For a blinking red check engine light, seek service as soon as possible. 

For a light that is not blinking, it is best to seek a diagnostic service within a week. Avoid any long or difficult trips until after the vehicle is examined. The diagnostic testing may reveal a problem which can be put off a bit longer, or it may indicate an issue that requires more immediate attention. It’s better to confirm there is nothing major wrong than risk the car breaking down somewhere and causing even more damage.

What Is the First Thing to Check When the Check Engine Light Comes On?

Start by checking the gas cap first, since that is easy to fix. Beyond that, it’s not a good idea to try and guess what the cause of the check engine light may be. The light coming on means there’s something going on with the car. A trained technician is able to run a diagnostic check and evaluate the automotive codes that come out of the testing to determine what’s going on with the vehicle. 

Is a Solid Check Engine Light Serious?

A solid check engine light can be serious, but not as urgent as a flashing red light. In most cases, the vehicle should be reliable enough to get to a mechanic shop for a professional evaluation. 

Why Is My Check Engine Light On but My Car Runs Fine?

Some problems are initially very subtle. The vehicle may be communicating that there‘s a problem before the driver can detect it. Some problems causing the check engine light to illuminate are not related to engine performance at all. It may simply be that a sensor is out. But the check engine light is the signal that the vehicle should be checked out by an automotive professional.

Can I Diagnose the Check Engine Light Myself?

Yes, vehicle owners can diagnose the check engine light at home with a check engine light code reader or scan tool, many of which are available for under $25. These monitors often include the words “universal OBD2 scanner” or “OBD2 scanner” in the name. The proper description is “OBD-II scanner.” 

A code reader is very basic. It can read and clear the codes. A scanner has more troubleshooting capabilities and can provide more information to help resolve the issue. Generally, scanners are more expensive. To use a code reader or scanner, you must plug it into the OBD-II port. This can usually be found under the steering column.

Unfortunately, these devices can’t ensure the problem has been fully diagnosed, and they don’t fix the problem. Learning how to decipher the code reader may help car owners communicate with mechanics better and also hold them accountable for necessary or unnecessary repair requests. It may or may not reduce the mechanic’s diagnostic fee.

What Will It Cost to Fix the Problem Indicated by the Check Engine Light?

CarMD lists the 10 most common check engine light-related repairs and the average cost to repair them (including parts and labor). Below is their list from the April 2024 report:

• Replace catalytic converter(s): $1,304
• Replace oxygen sensor(s): $253
• Replace ignition coil(s) and spark plug(s): $398
• Replace mass air flow sensor: $311
• Replace ignition coil(s): $212
• Replace EVAP canister purge control valve: $141
• Tighten or replace fuel cap : $25 on average to replace, free to tighten
• Replace ABS wheel speed sensor: $271
• Replace fuel injector(s): $446
• Reprogram powertrain control module: $109

Many of these problems lead to more serious and expensive repairs if left unaddressed. Some of them involve reduced fuel economy and/or performance each day the problem is not resolved, presenting a significant chance the situation will worsen over time. It’s rare that a malfunction repairs itself.

Can I Ignore the Check Engine Light?

Virtually every manufacturer and reputable automotive source advises car owners not to wait on getting the check engine light checked out. But many people ignore the check engine light for more than a week; some wait as long as a year. 

In a 2024 survey, CarMD found 49% of drivers have some kind of warning light on and 20% of drivers have the check engine light on. Some of the delays may be attributed to drivers not wanting to take the time to go to a mechanic, while others do not want to worry about the costs of the repair. The study found costs for parts increased 5.1% in 2023.

Why Do So Many Vehicles Have a Check Engine Light On and What Are the Consequences?

The U.S. national fleet of vehicles continues to age. The Bureau of Transportation reports the average age of all light vehicles was a record high of 12.5 years in 2023, 11.8 years for light trucks, and 13.6 years for passenger cars. On the supply side, this is partially due to vehicles lasting longer than they used to. On the demand side, there are millions of drivers using their cars longer to save money and avoid the costs of purchasing a new vehicle. 

Driving a late-model vehicle makes it more likely the car will develop a serious problem. In those cases, it would be more important to address an urgent repair than try to save money, especially because waiting often means spending even more money on costly repairs.

Every state has its own laws related to vehicle inspections. Some states (e.g., Delaware, Texas, Massachusetts, and Colorado) will not allow a vehicle to pass inspection with a check engine light illuminated. In North Carolina, a vehicle may pass a safety inspection with the check engine light illuminated if it has a 3-year emission exemption, but it will not pass an emissions test with the light on.

Road safety and a clean environment are important for all citizens. Part of the responsibility that comes with driving is properly maintaining the vehicles on the road in a way that keeps everyone safe.

Related Resources

• VIN Lookup
• All Cars for Sale
• Sell My Car
• Compare Cars
• Car Finder Tool
• Car Ratings
• New Car Previews
• Expert Car Reviews
• Car Trade-in Values