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Check Engine Light and Why It Turns On

Why Check Engine Light Is On

Although your vehicle can’t verbally talk, it can communicate with you. One of the top ways it does so is with your dashboard indicator light, especially the check engine light. 

The check engine light is a key part of your vehicle’s onboard diagnostics system, a super smart computer system. This system works around the clock to control and monitor your vehicle performance, such as fuel mixture, ignition timing, and engine speed.

When your onboard computer detects something is awry, you’ll see the infamous illuminated check engine light. Most drivers are terrified of the check engine light being on, but promptly addressing it can save time and money.

Iowa City Tire & Service is the leading auto repair center in Iowa City, IA. We offer a full range of auto repair solutions, including check engine light repair. Is the Check Engine Light Flashing or Static?

Is Your Check Engine Light Static or Flashing?

Before we dive into the causes of an illuminated check engine light, it’s important to distinguish between flashing and static lights. 

  • If the illuminated light is static, there is no need to pull over immediately or panic. It simply means that something is amiss. It’s usually not an indicator of a catastrophic engine problem.
  • If you see a flashing light, it means that your engine is under severe duress. You should have an engine diagnostics and maintenance performed as quickly as possible. Top Causes of an Illuminated Check Engine Light

5 Common Causes of an Illuminated Check Engine Light

Now, let’s look at illuminated check engine light and what triggers it. 

1. A Missing or Loose Gas Cap

If your check engine light is on, one of the first things you should do is check your gas cap. Failing to properly screw on your gas cap or leaving your gas cap off can trigger the light. 

This is because a vacuum seal should be created once you tighten your gas cap. If this seal isn’t established, the indicator light will come on. Fortunately, this is an easy fix.

2. A Damaged Catalytic Converter

The catalytic converter is an important part of your vehicle’s exhaust system. If you notice a check engine light and a rotten-egg smell, you will probably need to replace your catalytic converter.

Simply replacing the catalytic converter will not often solve the problem. That’s because most problems are caused by other issues, like a blown head gasket which can force burnt coolant vapor into your car’s exhaust.

3. Worn Spark Plugs

Spark plugs are tasked with igniting the mixture of air and fuel to generate combustion to power your engine’s cylinders. 

If your spark plugs are not adequately firing, it can lead to an engine mixture. This can cause a spike in hydrocarbon emissions and reduce the performance of your engine. Your vehicle will alert you through the check engine light.

4. Bad or Dirty Mass Airflow Sensor

The mass airflow sensor is designed to gauge the air entering your engine to ensure your vehicle has the correct air-fuel mixture. 

If your vehicle isn’t getting the correct air/fuel mixture, your engine may refuse to start or stall. And when your mass airflow sensor fails, the check engine light will illuminate. This is due to your onboard computer receiving a signal that something is awry with the engine’s air-fuel mixture.

5. Bad Oxygen Sensor

Like the mass airflow sensor, the oxygen sensor measures the amount of unburned oxygen in your vehicle’s exhaust. If there is too much or too little unburned oxygen, it can cause essential engine parts to fail. 

As such, a faulty oxygen sensor will trigger a check engine light. In fact, it’s one of the most common reasons why the light is illuminated.


When it comes to finding the best auto repair and maintenance services at the best price, Iowa City Tire & Service is a sure pick. We have an unwavering commitment to customer service and pride ourselves on going above and beyond!

We invite you to check us out. Stop by our shop at 410 Kirkwood Ave., Iowa City, IA. You can also call us at (319) 338-5401 for inquiries or appointments.