A check engine light illuminated in your vehicle isn’t always a sign of a major repair that needs to be done. Sometimes you can fix it in just a couple minutes, but sometimes it can take the expertise of a mechanic.

If you are one of those people who like to know what is going on with their vehicle, then there are some common things to look for when your check engine light comes on.

Here are the top five most common reasons why your check engine light is on and how you can fix each problem.


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  1. Loose or Damaged Gas Cap

Believe it or not, the gas cap is probably the most common reason why the check engine light comes on. Not having the cap tightened can cause the fuel vapors to leak out and cause some problems with the fuel system. It’s easy to forget to not tighten the cap at the gas station if you get distracted. Also, be sure and inspect the cap to ensure it’s not cracked anywhere. You definitely don’t want to lose valuable gas mileage or increase emissions for something so simple!



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The Fix: Retighten the gas cap and check for any cracks. The check engine light should turn off after a few minutes of driving. If the cap is cracked, you can buy a new one at an auto parts store at an inexpensive price.

  1. Bad Mass Airflow Sensor

This is the result of having a dirty air filter or one that was installed improperly. Since the mass airflow sensor indicates to the computer how much fuel to use based on the air coming in the engine, a bad one could cause your car to stall and create a reduction in gas mileage. Not getting it fixed right away could also lead to damage to the spark plugs, oxygen sensors, or the catalytic converter.


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The Fix: Replace the mass airflow sensor. It will cost you a couple hundred dollars to get it replaced, but this isn’t something you want to install on your own. It’s easy to do if you know what you’re doing, but you can also cause larger problems if it’s not installed correctly.

  1. Faulty Spark Plugs

The spark plug is what helps initiate combustion and starts your car’s engine. If you have a faulty spark plug, then it will misfire and the acceleration of your car will be a little rough. There isn’t much you can do to prevent a faulty spark plug. They aren’t designed to last forever and will generally fail after a few years or so. Until you get the issue fixed, you will probably experience reduced performance in your vehicle in different ways.


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The Fix: Replace them as soon as possible. Spark plugs are cheap and easy to replace. Drive over to your nearest auto parts store and pick one up. You may want to fix it right there in the parking lot, just in case you have any questions or need assistance. It may seem like it’s not a big deal, but you don’t want something small to turn into something much larger.

  1. Failing Catalytic Converter

The catalytic converter is important because it converts harmful materials, like carbon monoxide, into harmless materials. The main reason why it fails is that people don’t keep up with their regular maintenance. Having broken spark plugs or oxygen sensors are two reasons why a catalytic converter would fail. When it’s failing, you will notice that your car won’t accelerate as much when you press the gas pedal, not to mention a reduction in gas mileage. In addition, you won’t pass an emissions test for a state inspection.


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The Fix: This is something you need to have a mechanic fix right away. The average person can’t replace the catalytic converter, and it’s not cheap to do. Expect to pay a couple of thousand dollars to get it replaced. But since it’s a necessary part, the consequence of not getting it replaced could be a car that doesn’t work anymore.

  1. Worn Out Oxygen Sensor

The oxygen sensor monitors how much fuel gets burned. If you have a worn-out sensor, then it won’t provide the correct information to the computer, resulting in decreased gas mileage. Since most cars have multiple oxygen sensors, you’ll have to rely on an OBD reader to let you know which one needs to be replaced. This is another part that isn’t designed to last forever. An oxygen sensor will eventually wear out, no matter how good you take care of your vehicle. If you let it get to a point where it’s completely worn out, then you could cause further damage to the catalytic converter and cause the spark plugs to be faulty.


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The Fix: Buy a new oxygen sensor or let a mechanic replace it. It won’t hurt the oxygen sensor to drive for a few days with a faulty one, but it could cause larger problems if you delay for an extended time. Get it replaced right away for a couple hundred dollars, rather than waiting and potentially paying a couple thousand dollars due to the additional damage it could cause.


You may have noticed that many of these five problems are related to each other in some ways. If you don’t get one corrected timely, then it could cause another one to become damaged. That’s why it’s important to act as quickly as you can when your check engine light comes on.

There are definitely other reasons why your check engine light could be illuminated in your vehicle. These are some of the most common reasons, so be sure to run through this list when your light comes on. There’s a good chance that your problem will be on this list, but if it isn’t, then you may have to rely on an expert to help you diagnose and fix the problem.

About Author:

He is an auto mechanic and auto blogger. He has enthused automotive when he was a teenager Tim has 10 years experience in car repair and now he would love to share what he know about car for everyone.  He is writing a blog about OBD2 scanner name OBD Advisor


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