7 Most Common Reasons Your Check Engine Light Turns On

check engine light

“What does a check engine light mean?!”

If the check engine light in your car just came on, you might be asking yourself that very question at the moment. Nothing sends drivers into a panic quite like the sight of their service engine light.

In some cases, the light will come on for a relatively minor problem. But in others, it could be an indication that your car needs a major repair before you can get it back out on the road.

Either way, it’s a good idea to have your car checked out right after you first see the light pop up on your dashboard. Otherwise, you could potentially put your vehicle at risk by continuing to drive it around.

Here are 7 common reasons why your check engine light might turn on out of nowhere.

1. Gas Cap Is Loose

Did your check engine light come on a few minutes after you pulled away from a gas station?

If so, it might be on simply because your car’s gas cap is loose. Pull over, tighten your gas cap, and that should do the trick.

You might be surprised by how many people spend days driving around worrying about their service engine light being on when the only thing wrong is a loose gas cap. This is obviously a best-case scenario if your light ever comes on.

2. Spark Plugs Have Gone Bad

Spark plugs are some of the smallest parts inside your car. But they play one of the most important roles when it comes to starting your vehicle up.

When you put your car key into the ignition and turn it, your spark plugs create a tiny spark of electricity that is used to get your car up and running. Without spark plugs, your ignition would be incapable of creating the combustion that’s necessary to start your car.

Your spark plugs are actually very durable. They’ll last you for at least 30,000 miles in most cases, if not longer. But at some point, they will stop doing their job and need to be replaced.

If your service engine light comes on, it could simply be a sign that it’s finally time to give your old spark plugs a rest and replace them with new ones. This is another pretty easy fix that you might be able to do on your own.

3. Ignition Coil Is Shot

It takes a whole lot of power to create a spark in a spark plug to start your car up. Your ignition coil is responsible for providing your vehicle with the power that it needs when you turn your car key in your ignition.

There are a couple of things that can cause your ignition coil to go bad over time. Age is one of them. If your ignition coil is on the older side, it will no longer be able to provide your vehicle with the power it needs when you go to start it up.

Extreme heat is another issue that can compromise your ignition coil and stop it from doing its job. If either of these things impacts your ignition coil, you might notice your service engine light come on. It’ll be time to replace the ignition coil if it ends up being the cause of it.

4. Battery Is Experiencing Issues

If your car is more than a few years old, a check engine light probably won’t have anything to do with your battery. Older vehicles aren’t capable of keeping a close eye on your car battery.

But there are many new vehicles that are equipped with monitoring systems that are advanced enough to pick up on problems with a battery. If your battery is on the verge of dying on you, these vehicles will alert you about it with your service engine light.

The average car battery will only last for about four years before it needs to be replaced. After that, you might start to see your light turn on, indicating an issue with it. 

5. Oxygen Sensor Is Faulty

Does it seem like your car is burning through fuel a lot quicker than usual these days? This could be a sign of a faulty oxygen sensor.

Your oxygen sensor is in charge of measuring how much unburned oxygen is present in the exhaust fumes your car produces. If it’s not working, it’ll often cause your vehicle to burn up more gas than it actually needs, which will drag your car’s fuel efficiency way down.

Outside of affecting your fuel efficiency, a faulty oxygen sensor can also lead to problems with your spark plugs and your exhaust system. It’s a good example of why it’s so important to have your car looked at right away if your check engine light comes on.

6. Mass Air Flow Sensor Isn’t Working

When you’re driving around, your car will allow a certain amount of air to enter your vehicle and pass through the engine. Your engine needs to have a very specific mixture of air and fuel to function the way it should.

A mass air flow sensor is in place to calculate how much air your engine needs. The computer in your car takes the sensor’s calculations and figures out exactly how much fuel to use to balance the air out.

But if the sensor goes bad, your engine won’t have any idea how much fuel it needs. It’ll take a toll on everything from your fuel efficiency to the power generated by your engine.

A service engine light coming on might be telling you that it’s time to swap out your old mass air flow sensor for a new one. It could also indicate that you need a new air filter to protect your sensor.

7. Catalytic Converter Is On the Fritz

The catalytic converter in your car prevents your vehicle from doing too much damage to the environment when it sends exhaust fumes out into the world. It converts the carbon monoxide your car produces into carbon dioxide before it makes its way out your tailpipe.

Without a fully functioning catalytic converter, your car will produce dangerous fumes. It’ll also likely fail the emissions portion of a car inspection in most states.

Have your catalytic converter checked out if you ever see your service engine light come on. It could very well be to blame for it.

Don’t Ever Ignore Your Check Engine Light!

Dealing with a check engine light can be frustrating. Since there are so many things that can cause it to come on, you never know exactly what you’re walking into when you go to get your car repaired.

But you shouldn’t ever, under any circumstances, ignore your service engine light entirely. It could turn a small issue, like a bad spark plug, into a much bigger issue that requires extensive (and expensive!) repairs.

Read our blog to find preventative maintenance tips that you can use to keep your service engine light off.

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