Why Is My Check Engine Light On?

The first time I saw a check engine light, I was driving home from university at the beginning of one summer, with my little sister in the passenger’s seat next to me. I’d never seen the light on my dashboard before and I immediately panicked. The little light that looks like an engine obviously meant that my vehicle was going to explode if I continued driving it, right? And I was still two states away from home!

After consulting my owner’s manual, I discovered that while it did not offer a direct explanation for the check engine light, the light was not actually trying to tell me that my vehicle was about to self-destruct. Instead, it told me to take my car in to the dealership as soon as possible. I wasn’t ecstatic that the light didn’t give me any information about what was wrong with my car (for example, when the tire pressure light comes on, I know that one of my tires has low pressure and needs to be refilled). Still jittery, but at least not panicking anymore, I did exactly that.

They looked over my car, looked at its diagnostics, told me that they couldn’t find anything wrong, and just turned the light off. That was disconcerting, but ultimately, there was nothing else to do. I still wonder, to this day, what made that light turn on. If you’re wondering the same thing, here are a few of the most common check engine light explanations:

1. Your oxygen sensor needs to be replaced. Your car likely has a computer in it, did you know that? One of the functions of that computer is to monitor how much of your fuel has been burned, using an oxygen sensor. If this sensor is not working properly, the computer in your vehicle is not getting the right information. The sensor can get covered in debris and sludge in your busy engine and becomes less able to determine how much fuel and oxygen is being used, which will, in turn, decrease your fuel economy and make your car emit more dangerous gasses.


2. Your gas cap is faulty or loose. Your gas cap isn’t anywhere near your engine, right? So why would a loose gas cap cause your check engine light to come on? This is what the technicians at my dealership told me was the likely cause of my check engine light. When you do not screw it back into place properly or there is an issue with the gas cap, vapors created by your fuel will leak out of this area, which can wreak havoc on your entire fuel system. You’ll again see more emissions and less fuel economy. This is one of the most likely causes, especially if you do not feel like your vehicle is driving strangely or that there is anything else wrong with it.



3. You need new spark plugs. Your spark plugs are integral to the function of your vehicle, and if they are not working properly, your car is going to tell you about it by switching on your check engine light. You need functioning spark plugs in order to be able to start your car. When these plugs start to fail or misfire, you can feel it when you start your car. Pay attention and see if your car jolts a little bit when you accelerate. Your plugs are simply going to fail—it’s what they do. This is why you need to take your vehicle in to the dealership if your light comes on.


4. Your mass airflow sensor is faulty. This sensor’s job is to tell your car how much fuel the engine needs, based on how much air is in the engine. It is critical to a properly functioning engine and if it does not work properly, you’ll see that your emissions are increased and your gas mileage is decreased. If you do not regularly replace your air filters, you are going to see this becoming a more and more common problem. Replacing your air filters when you get an oil change is one of the best ways to make sure this never happens to you.


5. You need a new catalytic convertor. Your catalytic convertor is used to reduce the amount of harmful gas that your car emits. It will convert carbon monoxide into completely harmless gasses, which makes driving a car not as bad for the environment as it used to be before catalytic convertors were used in vehicles. If this part of your car starts to malfunction, you are going to see your check engine light come on. Not driving around for weeks or months with your check engine light on is integral to protecting this part of your vehicle. Issues with your catalytic convertor usually stem from faulty oxygen sensors of old spark plugs—issues your vehicle will already have been trying to tell you about.


6. You need a new thermostat. Your car’s thermostat determines the temperature of your engine, opening the valve to let in coolant when it is needed. If this device is not working properly, your check engine light will probably come on. A malfunctioning thermostat will probably lead to overheating and severe engine corrosion, depending on how long you drive with your check engine light on and do not take your vehicle in to be serviced.


If your check engine light comes on, the best thing to do is to take your vehicle in to your dealership as quickly as possible. While a check engine light does not always constitute an emergency, this is your vehicle trying to tell you that something is wrong and that the situation is, at the very least, urgent.

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