My Check Engine Light Is On! What Do I Do?

It's a beautiful night; the moon brightens the horizon, and distant heat lightning flickers across the sky. With your windows down, a gentle breeze calms you as you unwind on the scenic drive home, leaving the day's stresses behind. Suddenly, you look down at your dash, and relaxation turns to dread. Your Check Engine Light has turned on. In that moment, a whirlwind of thoughts race through your mind. Is your car okay? Are you going to be stranded on the side of the road when the storm hits? How will this impact your wallet? What do you do next?

Before you take the express lane to panic, take a moment to assess the situation. Your Check Engine Light can communicate different messages. To ensure that you are positioned to make an informed decision when your Check Engine Light comes on, it is important to educate yourself on the light’s primary functionality and the different messages it can communicate.

The Check Engine Light is a warning indicator for both the engine and your vehicle’s emissions system. This indicator light has been installed on vehicles since the 1930’s and was initially designed to indicate a major problem with the engine. However, since 1996, most cars have been manufactured with emission monitoring systems to track and measure the rate at which harmful pollutants are released from your vehicle. These electronic sensors monitor hundreds of conditions per second to ensure your car runs as efficiently and pollution-free as possible. When your Check Engine Light comes on, it is important to understand whether the indicator informs you of a critical engine issue or an emissions system malfunction.

What's the difference between a solid vs flashing check engine light

If your engine indicator light comes on, the first thing to check is its behavior. Is the light flashing, or is it solid? Knowing the difference between these two statuses will clearly indicate the severity of the problem.

Solid Check Engine Light: If your Check Engine Light is consistently illuminated, a malfunction affects fuel efficiency and emissions or could indicate an important mechanical issue. If the vehicle is running poorly, drive cautiously and address the problem immediately. You can take your car to an auto shop to get the code pulled so that you have an idea of what the root cause might be. Once you know the source of the problem, you can take the appropriate action to remedy the situation.

Note: Many auto part stores will "pull the code" for you at no charge but remember that they are in the business of selling auto parts. They cannot truly diagnose the issue; they can only tell you what parts or systems may have failed. Replacing a part related to your code will not necessarily fix your problem. It may require special equipment and expertise to replace after the code has been properly diagnosed.

Flashing Check Engine Light: Take immediate action if your Check Engine Light flashes. This means something is critically wrong in the system, and further damage could occur. Pull off the road safely and use your AAA Membership to contact AAA Roadside Assistance to help you get your car to an auto repair location.

Common reasons your check engine light is on

If your Check Engine Light turns on, a few common auto components could trigger this. Some are simple fixes, while others might be more expensive. Knowing what you could be walking into could help you better understand what you might have to spend to resolve the issue.

1. Loose or Faulty Gas Cap: Your gas cap and some of the fuel lines that make up your fuel system are designed to recirculate fuel vapors and prevent them from escaping into the atmosphere. A loose or faulty cap will trigger a malfunction in the emissions system.
2. Defective Oxygen Sensor (O2 Sensor): Your O2 sensor measures the amount of oxygen in your vehicle’s exhaust to determine how much fuel should be injected into it. If it is functioning properly, you will see greater fuel economy, and your engine will run more efficiently. However, if it malfunctions, fuel economy decreases, which could damage your spark plugs and catalytic converter.
3. Dirty Mass Airflow Sensor (MAF): The MAF is part of the fuel system and has similar functions to the O2 sensor. If it gets dirty or contaminated, it will trigger your Check Engine Light.
4. Bad Catalytic Converter: The catalytic converter is designed to reduce harmful emissions. If yours fails, you may not notice any issues with how your vehicle runs, but if you live in a state that requires vehicles to pass emissions tests, yours will fail.
5. Intake Vacuum Leak: Your intake manifold evenly distributes a fuel-air mixture to your engine’s cylinders. A cracked intake manifold or intake manifold gasket could cause your vehicle to misfire or backfire. Other symptoms could include black smoke from your exhaust or strange whistling sounds from your engine.
6. Bad battery or alternator: Both are critical to starting your engine. If your voltage drops, your Check Engine Light and possibly your Battery Indicator Light will come on.
7. Bad spark plugs or ignition coils: Both components ignite the fuel-air mixture in your engine’s cylinders. If these fail, you may notice a drop in your vehicle’s fuel economy, a misfiring engine, or a sluggish engine response.

Consequences of ignoring the check engine light

While ignoring your check engine light MAY not cause your vehicle catastrophic damage, there are consequences for neglecting even the smallest of issues. Some of the problems you may run into because of ignoring your Check Engine Light include:

• Increased Emissions: If your engine is not operating efficiently, your vehicle will produce higher emissions, releasing higher amounts of pollution into the atmosphere.
• Reduction of Fuel Efficiency: Several issues that could potentially set off your Check Engine Light will reduce your overall fuel economy. While not inherently bad for your vehicle, it is bad for your wallet.
• Issues Could Snowball: What starts off as a small issue, like a bad O2 sensor, could lead to the deterioration of your catalytic converter.
• Potential Safety Issues: If your light is flashing, you could be on the verge of a catastrophic failure that could endanger you and others. These issues could affect AC and braking and even cause you to stall in the middle of the road.

Fixing the root cause of a check engine light (DIY vs professional)

When the check engine light comes on, the best course of action is to address it immediately. The key is knowing whether you should attempt to resolve the issue yourself or take it to a professional for a diagnosis. If you have some experience with and are comfortable performing minor maintenance tasks, you may be able to repair the issue yourself.

Examples of minor repairs include:

• Tightening or Replacing the Gas Cap
• O2 Sensor Replacement
• Spark Plug Replacement

For more complex issues, it would be wise to take your vehicle to a professional. If you are looking for a reputable facility to diagnose the problem, consider taking it to a AAA-owned car Care location or AAA-approved auto Repair facility. They have the experience, expertise, and equipment to check your code and help you determine the next step to repair the issue.

Will the check engine light turn off on its own?

Unfortunately, a Check Engine Light is not known to turn off until the root cause that triggered it has been resolved. Even after fixing the issue, resetting the system with a code scanner is important. To ensure the problem is completely resolved, take your vehicle for a short drive after resetting the code. If the indicator does not turn on again after a few minutes, you can confidently return to your relaxing evening drive. 

Check engine light prevention tips

The best way to reduce your chances of dealing with the fallout of a Check Engine Light is by implementing preventative measures like:

• Tightening Your Gas Cap: Ensuring your cap is tightened properly after a fill-up will reduce fuel vapor evaporation, bolstering your emissions system and overall performance.
• Practice Safe Driving Habits: Driving aggressively puts unnecessary strain on your engine, leading to premature deterioration. Instead, drive responsibly, emphasizing safety over speed and hard braking.
• Purchase Quality Fuel: This will take some research, but not all gas stations and fuel grades are created equal. Some make higher-quality fuel to increase your vehicle's longevity and efficiency. It is important to know which carriers and suppliers are best.
• Perform Routine Maintenance: Oil changes, air filter replacements, spark plug checks and other routine maintenance procedures could help you reduce the likelihood of triggering your CHECK ENGINE LIGHT. Consult your vehicle’s owner’s manual to learn more about the manufacturer’s suggested maintenance schedule.

These preventative measures do not guarantee that you will never trigger your Check Engine Light; however, they will reduce your chances. Like with all things, it will last longer if you take care of it. If you use and abuse it, you will experience the consequences.

No one looks forward to their Check Engine Light coming on, especially on a nice breezy, relaxing drive. However, if you know what to watch out for and what the different indicators mean, you can make informed decisions for yourself, your wallet, and the health of your vehicle. Enjoy your drive!

Additional tips for other car dashboard indicator lights

• Red Engine Light: Safely pull off the road. This can be an issue with engine temperature (overheating) or low oil pressure. Continuing to drive can cause extreme, expensive damage.

• Tire Pressure Light: Most Tire Pressure Indicator Lights do not warn you until a tire is at least 25% low. Walk around the car to identify if any tires are flat or appear low on pressure. If all seems normal, check the air pressure in your tires as soon as possible. Tires normally lose around 1 pound of air every month; another pound is lost for every 10 degrees of temperature drop. For example, if your tires were inflated to 35 lbs in May, and in October, you have 75-degree days and 45-degree nights, you may have only 27 lbs. The best practice is to check air pressure at least once a month.