Can You Read Codes Without Check Engine Light On? (Full Guide)

Can You Read Codes Without Check Engine Light On

Do you know if you can read codes without the check engine light on? Well, you are at the perfect place to find the answer to such a question.

As you may well know when there are issues with your engine, the ‘check engine’ light may come on. The purpose of this light is pretty self-descriptive.

The light indicates that you have a problem with your engine or transmission, and you need to take your vehicle in for further inspection. 

A lot of people wonder whether their vehicle is keeping a record of errors, even if the check engine light isn’t coming on. That is something that we want to, hopefully, answer on this page. 

Can You Read Codes Without Check Engine Light On?

This is going to be dependent on your vehicle model. Most vehicle models will store codes, even if the light doesn’t come on right away.

However, you cannot expect these codes to be stored for the long term.

That is something that we are going to discuss in a future session. For now, let’s focus purely on whether those codes are going to be stored.

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What Is a Code?

A check engine light is just a light. While the light may come on, it doesn’t tell you exactly what is wrong with your vehicle. You, or preferably a mechanic, are going to have to diagnose the exact problem. This is where codes come in.

If you have a modern vehicle, there will be an onboard computer that is checking pretty much everything that happens. It will ensure that the engine is running properly. It will check whether your transmission is fine. 

If the onboard computer detects an issue, it will ‘log’ that issue. When it does this, it will create an error code.

Each error code is tied to a very specific issue. If the issue is severe enough, then the check engine light will come on.

How Do You Check The Codes For Your Engine?

Once again, this is going to be dependent on your vehicle. Some vehicles will actually display the codes for you right there on the odometer. You can flick through the manual for your vehicle to know exactly how to do this.

However, for the vast majority of vehicles, you are going to need a gadget known as an OBD. These aren’t too expensive, and you should probably keep one handy if you are serious about vehicle maintenance.

The OBD is a device that you can plug into your vehicle. It is the same tool that mechanics will use to work out what is causing the check engine light to come on.

So, if you had access to one yourself, you could deal with most minor problems without taking a trip to the local garage.

The main job of the OBD is to allow you to read any codes that have been stored by your vehicle. As we mentioned previously, you are going to be able to view both active and pending codes. So, even if that check engine light hasn’t come on, you will still be able to see whether your vehicle has any issues.

The second job of an OBD is to allow you to clear any codes for issues that you have dealt with. Although, this is not something that we would really recommend that you do unless you are 100% sure that you have rectified the issue. 

Does a Vehicle Store Codes, Even When The Check Engine Light Doesn’t Come On?

With most modern vehicles, yes. 

The ‘check engine’ light is only going to come on when your vehicle is in dire need of a service. If your vehicle was constantly informing you of every minor issue, you would forever be taking your vehicle in for a service.

This doesn’t mean that the vehicle isn’t recording every issue that happens, though. It keeps a log. Even if the check engine light doesn’t come on, you are still going to be able to read these codes. Although, there is a chance that these codes may not be stored for the long term.

This is something else that we will be discussing a little bit later on. 

What Is The Purpose Of a Vehicle Storing Codes?

So, why is the vehicle storing codes, even if the vehicle is not telling you of these errors? Well, there are a couple of reasons for it.

In most vehicles, the vehicle stores these codes so it is able to track if issues are getting worse. If the issues wouldn’t be large enough for an immediate service, when the error codes really start to stack up, your vehicle may decide to tell you to go in for a service anyway.

The main reason why codes are stored, however, is to make it a whole lot easier for a mechanic to diagnose a problem.

As talented as mechanics are, vehicles are incredibly complicated. While they may be able to get a rough idea of what an issue is based on what you tell them, they may not be able to get the full story.

By reading the codes stored on your vehicle, the mechanic is going to know immediately what the issue is. They can then get to work with fixing it. Basically, it speeds up the whole diagnostic and repair process. 

Is There a Difference Between Active and Pending Codes?

If you are able to read the codes yourself, then you will notice that some OBDs will list both active and pending codes.

Active codes are anything that has caused the check engine light to come on. Pending codes are anything that has happened in the past but hasn’t quite been serious enough to switch the light on.

However, if those issues return, then there is a strong chance that the light will come on as it indicates a problem with the engine or the transmission in your vehicle. 

How Long Are Fault Codes Stored?

This is going to be dependent on the vehicle model. You may want to read through the vehicle’s manual to know for sure.

In most cases, the fault codes are going to be stored as long as that issue remains present. Your vehicle may not necessarily tell you that there is an issue, but the codes will keep getting stored.

This means that when your vehicle finally goes in for a service, the problem can be fixed.

Some vehicles will eventually clear the error codes themselves.

For example, if there is a small issue that hasn’t come back (e.g. there was a loose gas cap at some point), then the code will be cleared. This will help to ensure that the vehicle isn’t incorrectly diagnosed when you take it in for a service.

Finally, the codes on your vehicle can be reset. However, you will not be able to do this yourself. You will need access to an OBD, which leads us neatly to the next section. 


Most vehicles will store codes, even if the check engine light comes on. Even if the check engine light hasn’t come on, you should still be able to read all of these codes.

However, with most vehicles, you are going to need access to an OBD.

You can either buy one yourself or get in touch with a garage that can carry out the diagnostics for you.  



Jeff is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Reatta. Jeff has been creating written and video content about transportation, automotive, electric cars, future vehicles as well as new, used for more than 18 years. Jeff is based in Boulder, Colorado.

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