Blog Car Issues & Diagnoses 6 Reasons Why Your Check Engine Light Might Be On

6 Reasons Why Your Check Engine Light Might Be On

January 20, 2020

You’re driving along, minding your own business, when out of nowhere, a light pops up in your dashboard. It’s the check engine light – one of the most dreaded sights known to humankind.

If you find yourself in this situation, we have both good news and bad news. The good news is: The check engine light doesn’t always mean something is horribly wrong with your car. The bad news is: The check engine light can mean there’s something horribly wrong with your car. Don’t worry, we’ll explain.

Why is My Check Engine Light On?

The check engine light can come on for many reasons. For example, something as simple as a loose gas cap can trigger the warning. And major problems, such as failed internal engine components, can turn on the light, as well. In order to really know what it is wrong with your car, it’s best to have a professional diagnose the issue.

The Check Engine Light: It’s More Complicated Than You Think

There are countless reasons why the check engine light might pop on. Your car’s computer will illuminate the warning whenever it detects a problem with the powertrain (engine, transmission, and related components) that could increase tailpipe emissions.

For instance, a faulty gas cap, which would allow fuel vapors to escape into the atmosphere, can trigger the light. Likewise, an internal engine problem that causes a misfire, and therefore increased hydrocarbon emissions, can also turn on the light. And to make things more complicated, because each car is different, what triggers the light can vary by year, make, and model.

In other words: There’s no way to say exactly why your check engine light is illuminated without performing diagnostic work.

When the check engine light comes on, your car’s computer, which is often referred to as a control module, will store a corresponding diagnostic trouble code (DTC) in its memory. A professional mechanic can use a scan tool or code reader to retrieve that code, then use it as a starting point to perform further troubleshooting.

What we can tell you is that the check engine light comes on for powertrain-related problems. Issues with, say, your antilock braking system will trigger the ABS light, rather than the check engine light.

Of course, nowadays, because various parts of a vehicle are closely interrelated, in some rare cases, a problem within one subsystem (e.g., the antilock brakes) can trigger warnings in another subsystem (e.g., the powertrain). But for the most part, the check engine light means there’s a problem somewhere in the powertrain or related components.

Common Reasons Why Your Check Engine Light Might Be On

With that in mind, let’s explore some of the most common reasons why your check engine light might be on.

1. Engine problems

It goes without saying that engine problems can trigger the check engine light. A control module monitors engine operation via a collection of sensors. And when it detects a problem, it turns on the check engine light.

2. Transmission problems

Your car’s transmission manipulates engine power and transfers it to the drive wheels. Because the two assemblies work together so closely, a problem with the transmission can also increase tailpipe emissions. Therefore, if the control module detects a problem with the transmission, it will turn on the check engine light.

3. Emissions equipment problems

Modern vehicles have a plethora of emissions equipment onboard. There’s the exhaust gas recirculation system, the catalytic converter, the evaporative emissions system – the list goes on and on. Each piece of the puzzle is designed to minimize tailpipe emissions, thereby, protecting the environment and making the world a safer place.

We won’t get into each of these components and systems individually because, frankly, there are too many to list. But trust us when we say an emissions equipment failure can easily turn on the check engine light.

4. Modules and sensors (electronic powertrain controls) problems

A wide range of sensors and modules govern today’s powertrains. What’s more, the modules communicate with one another over a vast data network. Issues with sensors, modules, networks and wiring can trigger the check engine light.

5. Air/fuel delivery problems

Your car’s engine needs the correct amount of both air and fuel to run properly. When it gets either too much or too little of one or the other, the control module will likely notice. The device then turns on the check engine light.

6. Ignition system problems

The ignition system includes the spark plugs, coil packs, and everything else needed to ignite the air/fuel mixture inside the engine. As you probably guessed, the control module monitors ignition system operation. And it will turn on the check engine light if it detects a problem.

What to Do if Your Check Engine Light is on

You won’t know what the check engine light truly means until you have your car diagnosed by a professional. The warning could indicate something simple and harmless – or something serious that could cause further damage to your vehicle.

As such, you don’t want to take any chances. If your check engine light is on, have a professional diagnose and repair the issue right away.