7 Possible Reasons Why Your Check Engine Light is On

Kam Thandi
June 1, 2023

Your car has many different systems in place that are always running checks on its performance. When something goes wrong, the sensors pick up on it and let you know that an issue has occurred by turning on a warning light. The check engine light is one of the most common warning lights that comes up on the dashboard and it can be frustrating when it happens. 

The main reason why a check engine light is a source of stress for drivers is that it can mean a variety of different things. If your check engine light is on, you could either have a simple, small problem that is easy to fix or something incredibly serious going on. Knowing some of the possible reasons why your check engine light is on can help you narrow things down and get your vehicle repaired as soon as possible. 

What is a Check Engine Light?

The check engine light in most vehicles looks like a drawing of an engine and will usually be either orange or red. When it turns on, this is an indication that something has gone wrong with the engine and it isn’t performing as it should. The check engine light can either be solid or flashing, with solid meaning that the problem is not pressing and flashing meaning that you should pull over right away and get your vehicle to the nearest shop. 

When your check engine light is on, it can be discouraging because it does not tell you a specific reason for the warning. Plus, if you live in a state where you have to pass a smog test for registration, you will not be able to do so until the problem is fixed and the light is turned off. Understanding some of the most common reasons why a check engine light is on will allow you to run some checks yourself before you take your vehicle into the shop. 

Possible Reasons Why Your Check Engine Light is On

While there are several different reasons for a check engine light to turn on, there are some that are more common than others. Generally, you can narrow down the cause when your check engine light is on by checking some of the simpler issues first. Finding the root problem and repairing it will turn the light off so you can get back on the road without any worries. 

Faulty Oxygen Sensor

When a check engine light is on, one of the most common causes is a bad oxygen sensor. Your vehicle needs a mixture of air and fuel in order to properly combust and the oxygen sensor, also called the O2 sensor, is responsible for making sure that mixture is perfect. When this sensor fails, your engine will either run too rich or too lean, both of which can cause engine issues. You may notice misfires, rough idling, or bad fuel economy if this is the reason your check engine light is on. Fortunately, this is a fairly easy repair and the light should turn off once the O2 sensor has been replaced. 

Loose Gas Cap

Another incredibly common reason why check engine lights turn on is a loose gas cap. Your car’s fuel system needs to be a completely closed vacuum in order to properly move the gas to the engine with the fuel pump. If your gas cap is loose, air will get in the system and the EVAP leak detector will turn the check engine light on. Since you are constantly taking the gas cap on and off to refuel, as soon as you see that the check engine light is on, you should check the gas cap. It needs to be turned all the way clockwise until you hear a click to create a tight seal and hopefully turn the light off. 

Catalytic Converter Issues

One of the most dreaded reasons for a check engine light to be on is a catalytic converter issue. If you live in a state that requires catalytic converters, an issue with yours could be the reason your check engine light is on. Catalytic converters use precious metals to filter and clean the emissions coming out of your vehicle’s tailpipe and if something is wrong with it, the emissions sensor will turn the check engine light on. Unfortunately, catalytic converters can be very expensive, so it is best to check for other issues before assuming the worst. 

Ignition Coil Failure

The ignition coils in your engine take energy from the battery and help convert it into the spark that is used to ignite the fuel in the engine. When one or more of your ignition coils fails, you will notice a change in how the engine runs. It will run rough or misfire and you may also see that your check engine light is on. Replacing the failed coil should turn the check engine light off and help your engine run normally again. 

Spark Plug Problems 

The spark plugs work in conjunction with the ignition coil in that they take the energy created by them and inject a spark in the combustion chamber. Your spark plugs are meant to be changed every 100,000 miles and will eventually wear out and stop producing the necessary spark to light the fuel and push the cylinder. This will produce misfires and you may also smell fuel coming out of the exhaust since it is not being burnt in the combustion chamber. 

Mass Airflow Sensor Issues

Like the O2 sensor, the mass airflow sensor measures the oxygen in the air and fuel mixture going into the engine. With this sensor, your vehicle’s computer will adjust the amount of air being let into the combustion chamber so it is at the exact right ratio. If your check engine light is on and your car’s engine appears to be running rough or is having acceleration issues, this could be a sign that your mass airflow sensor has failed. Getting it replaced will turn the check engine light off and help you avoid more serious damage to the engine. 

Failed Fuel Injector

For many years, vehicles had carburetors, which delivered the fuel and air mixture to the engine. However, fuel injectors have since taken over that job and are responsible for firing the gasoline into the combustion chamber. When one of your fuel injectors fails or gets stuck open or closed, the engine will either run too rich or too lean. If your check engine light is on, listen to your engine and try to listen for any hisses in the engine compartment or vibrations that weren’t happening before. This is a good sign that you have a failed fuel injector and it will need to be replaced.  

Get the Help You Need When Your Check Engine Light is On

If your check engine light is on, it is important to remember that it could be because of any number of issues. A check engine light does not necessarily mean that there is a serious problem with your vehicle, but it is best to be on the safe side. Get your vehicle looked at by a mechanic sooner rather than later to avoid more serious repairs down the line. 

If your check engine light is on, ServiceUp is here for you. With one easy-to-use dashboard to help you manage your maintenance, collision, and mechanical repair needs, it has never been easier to get your vehicle fixed by qualified, experienced technicians. Whether you need simple oil changes or major body work, ServiceUp will take care of everything and get you back on the road. Get an estimate today to find out how ServiceUp can help!

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