Check engine light usually stays until you fix it. But sometimes it can surprise you by turning on and then turning itself off without fixing it. In this case, you may be left wondering, what just happened? What does it mean when the check engine light comes on and off?
Check engine light comes on and off when your car engine has an issue. Even after the light clears and your car runs fine, you should get it diagnosed by a certified mechanic to help you find out what error activated the check engine light.
The following guide will share more in-depth details about check engine light coming on and off, what to do if you find yourself in this situation, and other helpful info and tips you need to know.
Why check engine light comes on and off on its own?
Check engine light coming on and then going off on its own indicates that the underlying issue has been corrected. But it also tells you there are issues with your engine and the trouble codes for this issue have already been stored in your car computer.
If you notice this behavior, you don’t need to panic. It happens all the time and many car owners have experienced it at some point. The light can pop on and go off on the same day or after a while. In some cases, the light will come on again after a while and then go off again.
The car computer is constantly running tests on all the sensors to see if they live up to their expected standard. These tests are always up and running when you’re driving your car.
If the computer detects that or more parameters of these sensors are violated, it will make the check engine light illuminate on your car dash.
If the issue detected is minor or intermittent, then it will most probably go through a number of test cycles. And if your computer can’t detect the issue again, it will just clear the error code (i.e., it gets logged in the history), and then turn off the check engine light.
However, if by “check engine light comes on and off” you mean the light is blinking on and of continuously, without stopping or for a few minutes, this is usually NOT a good sign.
It means that the vehicle computer system has detected a major issue relating to emissions or running condition.
Such an issue should be given immediate attention to avoid further damage to the related components. Next, we discuss how to fix the issue of CEL going on and off…
How do you fix a check engine light that comes on and off?
The best way to fix a check engine light that comes on and off is to have your car computer checked for the stored fault codes.
Our reasoning is that something might have triggered the check engine light to come and you should know it is to help you fix the CEL.
Even when the light turns itself off, the error code that triggered it will be stored in the computer memory and you can access it with an OBD II scanner and look it up on Google to see what engine problem it represents.
You may take your car to AutoZone or local auto parts store to help you scan the computer system for error codes. But we encourage you to take your car to a repair shop because they have much better computers for diagnosing your car for fault codes.
Unlike what most people think, simply resetting the check engine light by clearing the codes or disconnecting the battery doesn’t help much.
This is because the warning comes on when there’s a problem with the engine. And unless the problem is fixed, it will keep on turning on and going off after a while.
Why check engine light comes on and off randomly?
A check engine light coming on and off randomly points out an intermittent issue. One possible issue that may cause the warning light to go on and then off randomly is when the engine management system has a poor electrical connection or any other wire showing itself intermittently.
Other possible issues for the CEL randomly coming on and off include intermittent misfires, failing engine sensors, sticky or stuck valve faults, e.g. the exhaust gas recirculation (EGR) system or EVAP system.
The best way to solve the issue of intermittent check engine illumination is to take your car for a check engine light diagnostic test. This will help give you a clear picture of what part of your engine is problematic and needs to be attended to.
Why check engine light comes on and off but no codes?
Whenever the check engine light comes on, there must be an error code logged into your car computer. Even if you can’t find any codes, there’s still something going on with your car engine and you’ll still need to have your car checked for any issues with the engine.
Most individuals and auto parts stores use scanners that are only set up to access the generic OBDII codes. But the car manufacturers and auto mechanics have enhanced computers that are capable of reading those “hidden codes” and telling you what’s causing the light to come on.
Another possible cause is an issue with the OBD scanner being used to scan for the codes. This is especially true when you’re using a low-level scanning tool. It could be an old model or one developed in another country and may not be compatible with your car model.
You can try using another scanner to pull out the codes or paying the auto mechanic to use their advanced scanning devices to pull the codes for you.
Why does my check engine light come on and off for an O2 sensor?
Check engine light may come on and then go off if you have a lazy O2 sensor or a failing O2 sensor.
The work of an oxygen sensor is to regulate unburned oxygen in your car exhaust system, which is simply a way of managing fuel mixture. This is important to ensure your car doesn’t run too lean or too rich.
When the sensor starts to fail and can no longer regulate the car fuel mixture, your car emissions will go up, and check engine light will come on.
If your CEL goes on and then off and the code reader pulls codes that indicate a problematic oxygen sensor or emission control system issue, we advise you to fix it as soon as possible.
A reputable mechanic should be able to carry out a full diagnostic test on your car and identify whether the oxygen sensor is failing. If discovered early enough, the sensor can be replaced and save you a significant amount of cash in the future.
A quality O2 sensor costs you around $175 plus labor price. If not replaced on time, it may cause catalytic converter damage which is costly to replace.
What if check engine light came on and then went off after a week?
Check engine light may also come on and stay on for a week and then turn itself off. This happens because the problem that caused the light to come on has resolved on its own and the light consequently turns itself off.
As we have discussed before, your car computer is continuously running tests when you’re driving your car. If your car passes a test it has failed earlier, then the computer will register the error as resolved and deactivate the check engine light.
However, this doesn’t mean that you’re in the clear. We still recommend you take your car for a diagnostic test to establish what issues your engine could be going through. Remember that the check engine came on for a reason and that reason is still there even if it turned itself off and your car is running fine.
Have the mechanic scan your car and find out what fault codes it produces. If you notice any unusual behaviors with your car while driving, you should also mention them to your mechanic to help them with pinpointing the error and offering you the best possible repair.
What causes check engine light to turn on, then off, and then on again?
A case where the check engine light turns on and off and then comes on again means your car engine is experiencing an intermittent issue.
Intermittent issues are generally harder to diagnose and are even cited as one of the main causes of “No Fault Found” scan reports.
We advise you to have your car checked by your mechanic to see if they’ll get a history code to help diagnose what the problem is.
When the light is on, you should also pay close attention to how your car behaves. Do you notice any changes in the engine when driving it?
If yes, be sure to mention it to your mechanic to further help with diagnosis and finding the culprit behind the intermittent warning light behaviorIf your vehicle’s check engine light has been flashing on and off, it’s important to diagnose and address the issue before it becomes a major problem. While there may not be any diagnostic trouble codes stored, it’s still important to investigate further. Our articles on what to do when your check engine light is flashing but no codes are present and what a flashing traction control light means can help you understand the issue and take appropriate action. The article on what to do when your check engine light is flashing but no codes are present explains what this warning light indicates and what you should do when it appears. Meanwhile, our article on what a flashing traction control light means describes what this warning light indicates and how to address it. Check out our articles to stay informed and ensure your vehicle is running smoothly.
Frequently Asked Questions
The light may also come on and then go off if your car is suffering from an intermittent fault. You should have your car computer scanned for stored fault codes to help you find out what caused the warning light to come on.
The check engine light usually goes off after the fault that triggered it has been corrected. However, in some cases, the light can turn on and go off by itself if the problem resolves itself. The light can clear itself off after just a few minutes, hours, in a day(s), weeks, or even months.
Yes, you should still have your car checked even after the warning light goes off by itself. This is because the CEL usually comes on when there’s a problem. The light turning off on its own doesn’t mean the problem is gone, so make sure you have your car diagnosed to know the source of the light. This could help you catch a fault early enough and save you from having to incur high repair costs in the future.
Whenever your check engine light comes on and then goes off, it indicates that your engine has a problem that you need to look into. Even after the warning light goes off, the trouble code is logged into your computer memory and you should have your car scanned for the error codes. This will help you identify what issues triggered the check engine light and whether it needs to be repaired.
As usual, we recommend having an auto mechanic do a check engine diagnostic test rather than pulling the codes on your own and assuming what’s wrong with your car. Reputable repair shops will take their time to find the error codes and analyze your car engine until they find the problematic part and offer the best repairs so they can fix the issue of “check engine light comes on and off” for good.