Check Engine Light: 7 Reasons Why It May Be On & What To Do

As a driver, few things are more stressful than seeing that "check engine" light illuminate on your dashboard. Before you start to panic, you should know that check engine lights aren't always indicative of a major problem with your vehicle. This light is a part of your car's onboard diagnostic system; any time your check engine light comes on, it's because your vehicle's onboard computer has detected some kind of issue in the vehicle's emissions, ignition, fuel or exhaust systems.

These issues can range from extremely minor (such as a loose gas cap) to much more serious (like misfiring cylinders). Generally, a steady or solid check engine light means that a problem has been detected, but the issue is typically not an emergency. On the other hand, if your check engine light is blinking, the issue may likely require more immediate attention. In this case, it may be the best course of action to pull off to the side of the road and call a tow truck.

Regardless, the easiest way to find out why your check engine light is on is to have a diagnostic run using a tool known as an OBD-II. This code reader (carried by any reputable mechanic or dealership) plugs directly into your car's onboard computer to determine which of your vehicle’s trouble codes is causing the error.

So, what are some of the most common reasons your check engine light may be on—and what should you do about it?

7 Common Reasons Your Check Engine Light Is On

Why is your check engine light on? The reasons can vary greatly based on factors like your car's make, model year, and more. Again, you should always have the cause of your check engine light diagnosed by an experienced, certified technician at a trusted dealership or repair shop. The following are among the most common culprits for check engine lights illuminating in modern vehicles.

1) Engine Problems

This one might seem a little too obvious, but it's true—your check engine light could be on because your car's computer has detected an issue with your engine's operation. This could include anything from a bad fuel injector or failed spark plugs to a defective ignition coil.

In general, the most common engine issues will be difficult to ignore. You'll probably notice indicators like an ongoing engine misfire, vapors coming from your engine, or sluggish vehicle performance. Either way, you should not overlook true engine issues (like these), as ignoring them could cause further—and potentially more expensive—damage to your vehicle.

Action Steps for Engine Problems:

Because it can be damaging to drive your vehicle while its engine is misfiring or experiencing other obvious problems, it's best to pull off to the side of the road (when safe to do so). Call for a tow truck to take your vehicle to the nearest auto repair shop for a complete diagnostic. You may need to replace your spark plugs, fuel injector, or an ignition coil. In some cases, a leak in your engine's vacuum system can also cause similar issues—but these can be difficult to diagnose without the right experience.

2) Transmission Issues

Why would your check engine light come on if the problem is actually related to your transmission? Your check engine light may come on if your transmission is having issues because your car's engine and transmission work very closely together. In fact, the transmission plays the important role of transferring power from the engine to the drive wheels.

When transmission problems occur, it is common for tailpipe emissions to increase. Because the check engine light detects high levels of tailpipe emissions, it makes sense that this type of problem would cause the light to turn on.

Some common transmission issues that could cause a check engine light to illuminate include a malfunctioning solenoid (the part that regulates the flow of transmission fluid), low transmission fluid, or a transmission that is running too hot.

Action Steps for Transmission Issues:

If your car still appears to be driving normally after your check engine light comes on, you can generally continue driving without worrying about causing any further damage. Of course, you'll still want to have your car looked at promptly. However, if you're noticing that your transmission is slipping gears or is having difficulty shifting gears, you may want to slow down and have your vehicle looked at sooner rather than later.

3) Oxygen Sensors Failed

One of the most common causes of engine light illumination is a failed oxygen sensor. Specifically, your engine's oxygen sensors monitor the amount of unburned oxygen in your car's exhaust system. These sensors also adjust air and gasoline ratios as needed to maximize fuel efficiency and performance.

Over time, however, these sensors are prone to failure. Not only do they operate in extremely hot conditions, but they are constantly exposed to engine exhaust. When oxygen sensors fail, you may notice that your engine seems to be running rougher than usual. You might even notice that your fuel economy is suffering.

Action Steps for Failed Oxygen Sensors:

The diagnostic codes for failed oxygen sensors will make it obvious to any experienced mechanic when an oxygen sensor has failed. From there, you'll probably need to replace any affected sensors (sometimes, more than one can fail at a time). Fortunately, this tends to be a relatively quick and inexpensive repair. Still, it is vital to have this done sooner rather than later, as faulty sensors can cause damage to your vehicle's spark plugs and, over time, possibly even its catalytic converter.

4) Catalytic Converter Has Gone Bad

Speaking of your catalytic converter, here's another potential cause of an illuminated or blinking check engine light. Specifically, the catalytic converter is responsible for superheating tailpipe emissions and turning them into compounds, such as water vapor and carbon dioxide. The main purpose of a catalytic converter is to reduce emissions and protect the environment.

As a result, when the catalytic converter fails, your car's onboard computers will detect increased emissions levels. This, in turn, will cause your check engine light to illuminate. You'll probably also notice reduced fuel economy and sluggish engine performance. If your car runs through an emissions test, it will likely fail.

Action Steps for Replacing a Catalytic Converter:

It's important to note that, in general, catalytic converters do not fail on their own. Usually, an undiagnosed issue with another part of your vehicle will cause the converter to fail. For example, this could be the case if you have a bad oxygen sensor that you don't replace promptly.

With this in mind, you'll need to address this by not only replacing the damaged catalytic converter, but also by repairing whatever issue damaged your catalytic converter in the first place. Otherwise, you'll continue to blow through converters—which can definitely add up.

5) Air or Fuel Delivery Problems

Your car's engine relies on proper airflow to run smoothly. That's why your vehicle also has an important part known as a mass airflow sensor (MAF) that monitors the amount of air entering the engine. This sensor helps your car's computer determine how much fuel is needed to run the vehicle.

Over time, however, MAF sensors can become damaged by a buildup of dirt, oil, or other debris. This can cause the check engine light to illuminate. It can also cause the MAF to malfunction, allowing too much or too little fuel to enter the system. These issues can lead to other problems like reduced fuel economy and damage to other parts of your car.

Action Steps for Air or Fuel Problems:

If a diagnostic reveals a problem with your vehicle's MAF sensor, you'll need to have it looked at more closely by an experienced mechanic. In some cases, simply cleaning the sensor can resolve the issue. However, in other cases, the entire sensor may need to be replaced. Regardless, you should take action quickly to protect your vehicle from further damage and repair costs.

6) Ignition System Problems

For your car's engine to run smoothly, the air/fuel mixture inside the engine must ignite. If this cannot happen, your vehicle won't run correctly. Ignition system issues are a common cause of check engine lights coming on, but the exact problem can be difficult to diagnose. This is because there are so many components involved in a car's ignition system, ranging from spark plugs and coil packs to control modules and valves.

Action Steps for Ignition Problems:

The proper course of action for addressing an ignition problem that has caused a warning light will depend on what you're experiencing behind the wheel. Ignition system problems can be relatively minor or extremely urgent, so check to see if there are any obvious signs of a problem, like strange noises or your engine misfiring. If so, you'll want to stop driving, pull over (when safe to do so), and have the issue addressed as quickly as possible.

Otherwise, you can likely get away with scheduling a service appointment at your local repair shop. Depending on the cause and the severity of the issue, you may need to fix a vacuum leak, replace a bad valve, or swap out your spark plug wires. Regardless of how minor or major the issue is, you should not ignore ignition problems, as they can cause problems with other parts of your vehicle.

7) Powertrain Control Problems

Many of the powertrains that run today's vehicles are comprised of a system of sensors and modules in constant communication. Unfortunately, all it takes is one bad sensor, module, or network to trip a check engine light.

The good news about powertrain control module issues is that they are often as simple as a bad sensor or a shorted wire, which means repairs are relatively quick and easy. However, PCM codes can be difficult to diagnose because they can also indicate other problems.

Action Steps for Powertrain Control Problems:

As with any cause of a check engine light, it's a good idea to have PCM issues diagnosed by a trusted mechanic. From there, you may need to replace a shorted wire, swap out a sensor, or possibly even replace your entire PCM.

Drive Safe With These Tips and Get Coverage With Clearcover

As you can see, there are many reasons your check engine light can come on. While it's important to have your vehicle looked at by a mechanic as soon as possible, the good news is that most of these issues are not immediate emergencies.

Staying safe on the road is easier with the right car insurance. Clearcover is a tech-driven car insurance company that delivers exceptional coverage at a great price. Take control of your coverage and join other safe drivers in an auto insurance revolution by starting your quote with Clearcover today.