7 Possible Reasons Why Your Check Engine Light is On

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February 23, 2023
Kam Thandi

It’s one of the most dreaded sights for any car owner: the check engine light. It can be a source of anxiety and confusion, particularly if you’re not familiar with the inner workings of your vehicle. The check engine light is a notification that something is wrong with your car. It could be a minor issue or something more serious, but it’s important to get it checked out as soon as possible. In this blog article, we’ll discuss 7 possible reasons why your check engine light may be on and how to diagnose the issue.

First off, what is a check engine light?

The check engine light, also known as a malfunction indicator lamp (MIL), is an indicator that something is wrong with your vehicle. It’s typically a yellow or orange light that illuminates on the dashboard when your car’s engine computer detects an issue with one of the components. The check engine light is designed to alert the driver to potential issues so that they can be addressed before they become more serious.


If your check engine light is on, it’s important to determine the cause so that you can take the appropriate action. It could be something minor like a loose gas cap, or something more serious like a faulty oxygen sensor. Either way, it’s important to take the time to diagnose the problem and get it fixed.


Possible Reasons Why Your Check Engine Light is On

There are a variety of reasons why your check engine light may be on. Some of the most common causes include a faulty oxygen sensor, a loose gas cap, catalytic converter issues, ignition coil failure, spark plug problems, and mass air flow sensor issues. Let’s take a closer look at each of these.


Faulty Oxygen Sensor

One of the most common reasons why your check engine light is on is due to a faulty oxygen sensor. The oxygen sensor is a component that measures the amount of oxygen in the exhaust system. It helps the engine computer to determine the correct fuel-air mixture to ensure that the engine is running efficiently. If the oxygen sensor is not working properly, it can cause the check engine light to come on.


A faulty oxygen sensor can cause a variety of issues, such as poor fuel economy, increased emissions, and engine misfires. It’s important to get the oxygen sensor replaced as soon as possible to avoid any further damage to the engine.

Loose Gas Cap

Another common reason for the check engine light to come on is a loose gas cap. The gas cap is designed to keep gas in the tank and prevent it from evaporating. If the gas cap is not tightly sealed, it can cause a leak which can trigger the check engine light.


If your check engine light is on and you recently filled up your tank, it’s a good idea to check the gas cap to make sure it’s tight. You can also try replacing the gas cap to see if that resolves the issue.

Catalytic Converter Issues

The catalytic converter is an important component in the exhaust system. It’s responsible for converting harmful pollutants into less harmful compounds before they are released into the atmosphere. If the catalytic converter is not working properly, it can cause the check engine light to come on.

A faulty catalytic converter can cause a variety of issues, such as decreased engine performance, increased emissions, and poor fuel economy. It’s important to get the catalytic converter replaced as soon as possible to avoid any further damage to the engine.

Ignition Coil Failure

The ignition coil is responsible for converting the energy from the battery into a high voltage spark that is used to ignite the fuel. If the ignition coil is not working properly, it can cause the check engine light to come on.

A faulty ignition coil can cause a variety of issues, such as engine misfires, poor engine performance, and decreased fuel economy. It’s important to get the ignition coil replaced as soon as possible to avoid any further damage to the engine.

Spark Plug Problems

The spark plug is responsible for delivering the spark that ignites the fuel in the combustion chamber. If the spark plug is not working properly, it can cause the check engine light to come on.

A faulty spark plug can cause a variety of issues, such as engine misfires, rough idling, and poor fuel economy. It’s important to get the spark plug replaced as soon as possible to avoid any further damage to the engine.

Mass Airflow Sensor Issues

The mass airflow sensor is responsible for measuring the amount of air entering the engine. It’s used to help the engine computer determine the correct fuel-air mixture. If the mass airflow sensor is not working properly, it can cause the check engine light to come on.

A faulty mass airflow sensor can cause a variety of issues, such as poor fuel economy, engine misfires, and increased emissions. It’s important to get the mass airflow sensor replaced as soon as possible to avoid any further damage to the engine.


Get your check engine light diagnosed

If your check engine light is on, it’s important to determine the cause so that you can take the appropriate action. It could be something minor like a loose gas cap, or something more serious like a faulty oxygen sensor. Either way, it’s important to take the time to diagnose the problem and get it fixed. If you’re not sure what the issue is, contact ServiceUp to get your car diagnosed quickly. We'll provide you with an estimate only for the repairs you need and get you back on the road before you know it.

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