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Why Is My Check Engine Light On? 10 Possible Reasons! 

How To Sell A Car With A Check Engine Light

When the check engine light comes on, it comes on suddenly without any previous warning signs most of the time. You might not know a lot about the check engine light but, you can tell that the problem could be a little serious.

Auto Repairs Are EXPENSIVE

Several owners might run quickly to the repair shop whenever they see a check engine light illuminating. However, the problem could be simple enough to get fixed by the driver himself. On the other hand, some check engine lights problems can be very complicated, and you might not even be able to drive the car to the repair shop.

This article highlights the 10 possible reasons to answer your question of “why is my check engine light on?” It's important to get any of these problems repaired even if it takes a lot of time, effort, over money. 

Leaving a problem causing a check engine lights illuminating might lead to more significant issues that could damage major components of your vehicle. 

Why is my check engine lights on? 


Your vehicle's internal computer uses the check engine light to indicate internal problems in your car. Some of these problems might be very simple and can't be repaired by the driver himself. In contrast, other problems might be a little more complicated and require immediate professional mechanics attention.

Here are ten possible reasons why your check engine light illuminating is: 

  • An issue with the fuel cap 


When you see the check engine light illuminating, you don't need to panic because the problem can be as simple as a loose fuel cap.

If you don't have an OBD2 scanner that could tell you the actual root of the problem, you could try to tighten the fuel cap and see if the check engine lights turn off by themselves. 

If the check engine light did not go away, the problem could be related to something else. 

  • A problem with the spark plug 

Your vehicle's parked lock is responsible for providing the required spark at the right time and amount to ignite the air-fuel mixture.

Overtime views, these spark plugs might wear out where they cannot respond quickly to the vehicle's requests. As a result, your check engine light might aluminate, indicating an internal problem with the spark plugs.

If you failed to replace the spark plugs on time, you might introduce complicated problems like a completely damaged catalytic converter. Repairing a spark plug is much cheaper than replacing a whole catalytic converter, one of the most expensive repairs for vehicle maintenance. 

  • Check the ignition coils 


Ignition coils are responsible for converting the battery's voltage into a higher voltage to get the electrical system starting.

With a faulty ignition coil, you might notice an engine misfire, and your vehicle will right roughly. About ignition coil can cause the check engine light to illuminate.

Unfortunately, to determine whether it's the ignition coil or not, you must have your vehicle inspected by a professional mechanic who could tell you the actual root of the problem.

If you have an OBD2 scanner, you can run a quick scan and check whether the problem is coming from an ignition coil or not. 

  • Both faulty spark plugs and ignition coils 


If you have confirmed that the problem is coming from a spark plug, this doesn't necessarily mean that the ignition coil is good.

In most scenarios, when the ignition coil gets bad, it can be associated with a spark plug problem.

Therefore, it's important to make sure that the problem is not happening due to multiple faulty parts at the same time. 

  • A bad catalytic converter 


About catalytic converter usually happens due to an issue with another component, and most likely, it's the spark plug or the ignition coil.


While the check engine lights should illuminate immediately after the spark plug or the ignition coil gets damaged, the problem might get complicated and reach the kettles of the converter to damage it. 

The catalytic converter is a major component in your vehicle. You cannot ignore this problem with a bad catalytic converter engine misfire and a significant reduction in vehicles' fuel economy.  

  • A failing oxygen sensor  


The oxygen sensor is responsible for measuring the quality of oxygen that was not burnt in your car. Your vehicle's internal computer uses this information to determine how much oxygen should be sent to the cylinders to maintain the correct air-fuel race.

Over time of use, the oxygen sensor can also wear out and get damaged. As a result, you will notice a significant difference in your vehicle's overall behavior, and the check engine lights can illuminate immediately. 

To get the problem resolved, you must replace the sensor and follow the recommendations in the user's owner's manual. 

  • An issue with the mass airflow sensor 


Like the oxygen sensors job, the mass airflow sensor is responsible for calculating how much air is going to the engine so the vehicle can send the required amount of matching fuel.

If the airflow sensor got damaged, you would notice a significant drop in the overall vehicle's efficiency and fuel economy.

To get the problem resolved, you must immediately replace the mass air flow sensor to save on gas and prevent damaging other combustion system components. 

  • A weak battery 


A faulty car battery might also cause the check engine to eliminate. In most scenarios, car batteries must be replaced within three years of purchase. However, if the battery got exposed to extreme weather conditions, it's lifespan might get shorter.

If that's the case, you need to replace your vehicle with a better battery, and you could either use a used car battery or a brand new one. 

  • A problem with the exhaust gas recirculation


Sometimes an issue with exhaust gas recirculation might cause an engine misfire, engine hesitation, and rough idling. All these problems could eventually lead to the check engine light illuminating.

If you've ignored the issue with exhaust gas recirculation, you might introduce more complicated problems related to reducing fuel economy, drop in vehicle performance, and failing the emission tests. 

  • A leaky vacuum hose 


We want to highlight the last problem related to cracks and leaks in the vacuum hoses. These hoses store evaporated gases and prevent them from coming back to the engine's block.

Over time of use, it's very likely to deal with cracks resulting in gas vapor escaping the engine block and causing your vehicle's internal problems. As a result, your check engine light might eliminate.

To get the problem resolved, you must consult a professional mechanic and identify the locations of vacuum hoses leaks and get them repaired. 

What to do when the check engine light illuminates? 


While there are many reasons for the check engine light illuminates, there is a common response you need to do whenever you see a check engine light illuminating.

This section highlights some advises and steps that you could follow in dealing with a check engine light illuminating:


  • Try and lower speed, lower the loads, and pullover


Immediately after you notice the check engine light illuminating, it's recommended that you drive slower and reduce any heavy loads on your vehicle. You might even need to slow down and pull over if you can. If you are driving on a highway, you might need to take the first exit to pull over on the side and stay safe at the same time. 

  • Tighten your vehicle's fuel cap 


As we mentioned earlier, one common problem for the check engine light illuminating might be related to a loose fuel cap.

Once you pull over safely, try tightening the fuel cap and see if the vehicle's check engine light stops illuminating. 

  • See if your vehicle has built-in diagnostics features 


If you are driving a modern vehicle, you might find that it has some built-in diagnostics features that you could refer to and check the cause of the problem. 

  • Use an OBD2 scanning tool 


If you have an OBD2 scanning tool, this might be the right time to take advantage of it and use it.

Plugin the tool to the OBD2 port and have it scan your vehicle's internal errors.

If your tool is advanced enough, it can tell you many details about your vehicle's problem. However, if it's basic, you can read the code and search through the Internet to see what the problem is related to. 


Your vehicle's check engine light is responsible for telling you if there is an internal problem with your car. As a result, you would never want to ignore an illuminating check engine light.

Some of the reasons for the check engine lights illuminating might be minor and can be resolved by simple actions like tightening the fuel cap; others might be more complicated and could results into your significant internal problems if you even try driving the vehicle.

It's recommended that he take care of the problem causing the check engine light to illuminate as soon as possible to prevent any significant problems in the near future that might require high repair costs. 

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