Why your check engine light is on

So you’re driving around town running errands when a shiny new light appears on your dash. Your heart sinks as you realize that it is the check engine light. No it doesn’t mean pull over and pop your engine to make sure the engine is still there. There are multiple reasons why your check engine light might be on.

The first thing to do would be to see if the check engine light is blinking or solid. If the light is blinking you should pull the car over because it could mean that there is an emergency failure. Otherwise in most cases you can drive to the nearest auto parts store or mechanic’s shop to get some diagnostic done. Usually auto parts stores will scan the car for free.

In most cases when the solid check engine light comes on there are five common causes.

Oxygen Sensor

The first part on our list that could be the root cause of your check engine light is your oxygen sensor. In most vehicles there are two to four oxygen sensors that test different things from air-fuel ratio to catalytic converter efficiency. In other words they tell your engines computer that it is using too much or not enough fuel. It can also tell your computer’s ecu that the catalytic converter is not working correctly.

Sometimes these oxygen sensors go bad and they should be replaced. With a bad oxygen sensor the car’s computer can’t get the right data to figure out if the car needs to run more fuel or not. Due to a faulty sensor your car’s gas mileage might be decreased. Also if left untreated it can cause issues to your catalytic converter which can come with a hefty price to replace.

The code reader in most cases will tell you if the upstream (before the catalytic converter) or the downstream (after the catalytic converter) is bad. Oxygen sensors are fairly simple to replace. With some mechanical knowledge and the correct tools you might be able to complete the project yourself.

Faulty or loose gas cap

Another fairly common issue, and the second part on our list is an evap leak. Usually associated with a faulty gas cap. The fuel system is closed. When there is a leak of fuel vapor it can cause issues. If you recently filled up on gasoline and the light came on you should make sure that your cap is tight. It’s good to make sure that the gas cap clicks a few times to confirm it’s sealed.

If the gas cap is tight there could be a possibility that the seal is bad. Alternatively there could be a crack or issue with the cap, You can do a visual inspection for any issues with the cap. If the light doesn’t go away you can purchase a replacement gas cap at your dealership or local auto parts store. They are fairly inexpensive.

Catalytic Converter

The next common problem on our list is the Catalytic converter. Used to clean the emissions of the vehicle, the Catalytic Converter is usually a metal container that contains platinum. As the exhaust gasses enter the Catalytic Converter the converter converts some of the gases into harmless compounds which exit the exhaust. With a bad Catalytic Converter you might not have much power when you press the accelerator.

If you have a bad catalytic converter you might also see a decrease in gas mileage. There are multiple reasons why a catalytic converter can go bad. Faulty oxygen sensors and deteriorated spark plugs are sometimes the cause of bad catalytic converters. Unfortunately some catalytic converters aren’t inexpensive to replace so make sure that you keep up on your maintenance. Regularly scheduled maintenance should prevent you from having this issue.

Mass Air Flow Sensor

Most modern cars are equipped with a Mass Airflow Sensor. The sensor’s job is to detect how much air is entering the engine. If the sensor is bad it will not be able to relay the correct information the the car’s computer. Therefore the computer will not know how much fuel to add.

With a bad Mass Airflow Sensor your vehicle can stall, increase emissions or decrease gas mileage. If the sensor is bad it can sometimes be cleaned with a Mass Airflow Sensor spray. If you clean the sensor and you’re still getting the issue you might need to replace the sensor.

Jiffy Lube Mechanics Were Arrested for Tampering.

A good way to prevent the Mass Airflow Sensor from going bad is to regularly change out the air filter. The air filter is a very important part of your engine. It cleans the air before it enters the engine. You wouldn’t want to breathe dirty air and neither does your engine. By replacing the air filter you can keep contaminants from entering your engine and harming other parts.

Spark Plugs, Wires/Coils

If you scan your vehicle and you’re getting one or multiple misfires the problem could be plugs and wires. Unlike diesel engines gasoline engines come equipped with spark plugs. While the vehicle is running the spark plug’s job is to ignite the fuel to push the piston down and rotate engine. If the spark plugs are not working correctly you might get misfires or the car may not stay running at all. You might also have a drop in power if the plugs are bad

Spark plugs are relatively easy to replace if you have the right tools. The electricity is sent though the sparkplug wires. In newer cars coils send electricity to the spark plugs which ignite the fuel. If the wires or coils are bad the may not be sending the electricity to the spark plugs. Depending on the misfire you might need to replace all or some of the wires/coils


We hope that we have provided some insight as to why your check engine light may be on. Hopefully you are able to fix and replace the parts yourself. If not you will be better educated when you take a trip to your local mechanic. Please like and share this so we can continue to make entertaining and educational posts.

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