5 Reasons Why Check Engine Light Come On after an Oil Change

I absolutely hate it when I finally get my oil changed and the mechanic says that there’s another issue with my vehicle. When the check engine light comes on after an oil change, it means that there is a brand-new issue you have to deal with. Luckily, I know a lot about the issues that appear after an oil change, and I’ll tell you how to fix them.

Why would my check engine light come on after an oil change?

So, let’s go over the scenario. because I’ve been there many times. I know you have been there as well. You finally take your vehicle into your favorite mechanics’ shop. Now, you paid a lovely person for an oil change. It’s about half an hour or so to a snack from the nearby stand. 

Then you sit in the waiting area and scroll through your phone. In no time, the mechanic says they are done. You check out your vehicle and jump back in your car. A day or two later, the check engine light appears and it’s a brand-new headache you have to deal with. 

So why does the check engine light come on after an oil change? Does that mean that the mechanic did something incorrectly? Did they rig it so that you have to come into the shop so they can charge you more money? Or is there an actual issue?

Actually, there are a couple of different reasons why your check engine light would come on after an oil change. I have dealt with most of these issues.

The gas cap is loose or is not on.

Did they put the gas cap back on? That’s a silly reason for the check engine light to come on. But it is important to have it on. You don’t want debris and particles to fall into the chamber that stores your motor oil.

Call the mechanic and ask if your gas cap is sitting somewhere on the floor. If they don’t have it, then ask for someone politely. They’ll give it to you as it is their mistake. If the gas cap is on but it’s very loose, just tighten it yourself.

There’s an issue with the airflow sensors.

The purpose of an airflow sensor is to send the right amount of air into the engine. The air has to mix with the appropriate amount of fuel sitting in the engine. The fuel is just waiting for the combustion process to start.

If the airflow sensor is not working the right way, it won’t send the right amount of air to mix with the gasoline. Because of the poor air-fuel mixture, your vehicle will begin to stall or turn off when idling. 

The airflow sensor needs changing about once every year so it may be time to change them out.

There’s no motor oil in the oil chamber.

Yes, this happened to me about 2 years ago. I went to my mechanic so they could give me a standard oil change. They drained out all the old oil and then forgot to add new oil. However, I found this out while I was driving home from the mechanic shop. My car had to stop completely. Luckily, I wasn’t on the freeway, and I pulled over to the side of the road. It was a total disaster.

At the first sign of shaking or high screeching noises, turn around and go back to the mechanic shop. If there is no motor oil in your engine, your engine will start to break down quickly.

The catalytic converter is malfunctioning

Unfortunately, a malfunctioning catalytic converter must be replaced. And to make matters worse, replacing the catalytic converter is expensive. The purpose of this part is to partially destroy gases and harmful fumes created by the combustion process. It reduces the number of pollutants so the emissions can go into the air. If you notice that you cannot accelerate or speed up as fast as the vehicle used to, this is another sign. 

You need to have your catalytic converter replaced.

If this is the reason why the check engine light is on, say a prayer and kiss your wallet goodbye. The average cost for replacing a Cadillac converter can be anywhere from $1,000 to $2,400

There’s something wrong with the sensors that set off the check engine light.

Perhaps nothing is wrong with your vehicle at all. The only problem is the check engine light itself. The reason why the check engine light could be going off when there’s nothing wrong at all is bad wiring or loose connections. Rent-A-Center is not attached to the area it should be monitoring, it will send a signal to the check engine light. So, everything could be running smoothly, but a sensor cannot pick up what it is supposed to sense. 

If you have diagnostic tools at home or you know how to use your computer diagnostic system, you can do it yourself. You can find out if the check engine light is the result of a misplaced sensor. Believe me, I would rather have a misplaced sensor setting off the check engine light than a faulty catalytic converter!


So, the issues above are the most common reasons for a check engine light turning on after an oil change. So, the next time you go to your mechanic and get an oil change, you can also ask them for a quick diagnostic test. This will allow you to see if there are any issues currently happening in your vehicle. 

I mean, you might as well ask since you’re already there. Also, in case there ever comes a time, ask them about the price of their catalytic converters along with the installation cost. You need to shop around and know the prices of other local mechanics; in case you ever end up replacing the converter.

  • Eric Williams

    I'm the founder of Daily Car Tips. I wrote articles in the automotive industry for more than 10 years, published in USA and Europe. I love sharing my knowledge and insights with fellow enthusiasts. Join me on this journey as we explore the exciting world of cars together!

    View all posts