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What does the check engine light mean and why does it turn on?

There is nothing worse than driving your vehicle down the road and having the check engine light (CEL light) turn on. It leaves you wondering, what is wrong with my vehicle, is it safe to drive. Let’s find out what does the check engine light mean.

Your CEL light illuminates when a control module detects that there is a problem with one of the systems on your vehicle. The Powertrain Control Module (PCM) monitors items related to the engine and transmission systems.

The PCM is capable of completing ongoing calculations that allow the fuel injection, air intake, and emissions control systems to work in harmony. They ensure that your vehicle is running in peak performance at all times to ensure that your vehicle gets the best fuel mileage. It also ensures that your vehicle emits the lowest amount of emissions possible during different driving conditions. 

As the PCM monitors the various inputs it also makes sure that all the systems are working correctly. These parameters are programmed in the Powertrain Control Module at the factory when it is built. If the vehicle starts to operate out of the designed limits the Check Engine Light will illuminate. This indicates that there is an issue with your vehicle and you need to repair the problem.

What is On Board Diagnosis (OBD)?

Simply put, On Board Diagnosis is what gives mechanics the ability to check why your CEL light turned on. 

On Board Diagnosis, or otherwise known as OBD is the ability for a vehicle to monitor and provide self diagnosis. It also provides the ability for a technician to access vehicle information. As well as important data to diagnose these vehicle systems.

In the 1960s the California Air Resource Board (CARB) along with the EPA, ISO, and SAE started work on a common standard that all manufacturers could use. Before this standard was released. It was common for manufacturers to use their own communication ports making it difficult to diagnose these vehicles. 

Starting in 1996 all vehicles sold in California were required to be equipped with OBD 1. Through the years this standard has been updated and vehicles today are now equipped with OBD-II which has many more functions when it is  compared to OBD 1. 

Flashing vs. Solid Engine Light

There are two different ways that your CEL light will illuminate in your vehicle. You will either see a solid or flashing light. 

In my experience in the industry I have noticed that a  solid CEL light is most likely what you will see. However, both can and will happen.

If the light is on solid this means that the Powertrain Control Module has found that there is a fault in an engine related system. It could be something as simple as you forgot to put your gas cap back on after filling. Or, worse, it could mean your catalytic converter is failing. 

If the CEL light is flashing you need to pay attention. If it is flashing it means that your Engine Control Module has found a catalyst damaging fault. This means that if you continue to drive your vehicle the catalytic converter of your vehicle will become damaged. 

The flashing CEL light is trying to get your attention. It is trying to get you to the side of the road as soon as it is safe. Once you are stopped, call a tow truck, your driving is done until you can get it repaired. 

Is it okay if I drive my vehicle with the check engine light on?

If your your engine light turns on solid, you can continue to your destination. Continue to your destination, monitor all the gauges and lights. If other trouble lights illuminate, ensure you pull over and stop as soon as it is safe. 

Is your engine light flashing, like mentioned above. You will need to get off the road when safe and call a tow truck. The cause of this will need to be repaired before driving your vehicle further. 

Whether your  check engine light is on solid or flashing, we always suggest that you get your codes checked as soon as you can with either an OBD-2 code reader or a professional mechanic. 

Depending on the advice of your mechanic and what is wrong with your vehicle you may be able to continue to drive the vehicle while waiting to repair it. Or, if there is something very wrong with your vehicle. You will need to get it repaired before driving anywhere. 

Check out the diagnostic codes section of our website. Here we go in depth about what codes mean, what can cause them, and even possible fixes. 

How to turn off your check engine light?

Just like the engine light turns on for many different reasons there are different ways that you can turn off the engine light. 

The Powertrain Control Module has the ability to turn off the engine light just like it can turn on the engine light. Even when the  Powertrain Control Module turns on the engine light it continues to monitor the performance of all vehicle systems. If the parameters that caused the original engine light to turn off, go back to normal. The engine light will eventually turn itself back off. 

If you have a fault in one of the systems of your vehicle, say an bad valve causing a misfire. The tests that the Powertrain Control Module continues to run will continue to fail. If you find yourself in this situation you will need to either repair the problem yourself or get it repaired by a knowledgeable mechanic. 

Once the repair is complete the mechanic will take an OBD-2 scan tool and attach it to your vehicle. Once attached the tool will communicate with the Powertrain Control Module. You can then clear the codes and voila, the engine light will turn off.

Can I turn off my own check engine light?

Here is a method that you can use to attempt to turn off your own check engine light:

  1. Turn key off and pop the hood
  2. Using the necessary tools, remove the negative cable from the battery 
  3. Position negative battery cable so it does not touch the battery
  4. Let sit for 10 minutes
  5. Re attach negative cable to battery
  6. Turn the ignition on.
  7. If check engine light is still on you will need to clear with an OBD-2 Code Reader

Is the check engine light still turned on when you turn the ignition back on you will need to see a mechanic. There may be something on the vehicle that needs to be repaired to repair the problem. 

John Morris
John Morrishttps://autoknowit.com
John Morris is the technical editor for AutoKnowIt.com. His years of experience in automotive repair as well as an automotive professor have prepared him to ensure that even the most technical information is accurate and concise at all times.

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