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Check Engine Light on and Off: Everything You Need to Know 

Check Engine Light on and Off: Everything You Need to Know 

Every driver has had to deal with a check engine light coming on at some point in time. It's one of the most dreaded warnings that you can see pop up on the dashboard display. When it does show up you definitely want to get it checked out sooner rather than later, but the problem is you often have no idea why it turned on in the first place. There could literally be hundreds of different reasons why a check engine light is going to pop up on your dashboard with no more clarification about why it showed up beyond the light being there. And if your check engine light is turning on and off, it can be even more frustrating.

Auto Repairs Are EXPENSIVE


A check engine light could pop up on your dashboard because you have a problem with your oxygen sensor, your catalytic converter, your spark plugs, your EGR valve, the list really does go on and on. That's exactly why it's so frustrating when you do get a check engine light because it could mean so many different things. The only way to know for sure is to either head to a mechanic so they can properly diagnose the reason why it turned on or use your own OBD2 scanner to diagnose the problem at home the same way that a mechanic would do it.


 Normally your check engine light will stay on until you actually do get the engine checked. Once the mechanic is able to diagnose the problem and address it then the light will turn off and you will not have to worry about why the warning is there any longer. But if the light is turning on and off on its own that can represent a whole new set of frustrations for you as a driver.


Why Would My Check Engine Light Go on and Off?


In modern vehicles the check engine light is governed by your car's computer. Your computer is constantly checking every sensor that is connected to it to make sure that your car is running as well as it can. This can include sensors that measure air intake, fuel pressure, oxygen, wheel speed, and much more.  it's possible that any one of these sensors at any given point in time could be failing as a result of its age, or the wires that connect it to your car's computer could be broken or coming loose. The sensor itself could also have been damaged or in some cases it could have even just gotten dirty and it's no longer able to transmit the correct data to your car's computer.


If there's a loose connection to one of your sensors, or if one of the sensors is covered in road grime or buildup of some kind then that could trip the check engine light. The data from the sensor will not transmit properly to the computer and the computer will alert you by setting the check engine light off on your dashboard. However, the next time your computer tries to check the data from all the sensors if the sensor is no longer dirty because whatever was on it came off, or if the loose connection is properly aligned again so that the data is transmitting correctly, then your computer could be getting the correct information once again. If that happens, the check engine light will turn off because there's no problem.


 Because there are so many reasons why a check engine light can go on it's hard to say why the light would turn on and then turn off again without you actually taking it into a mechanic to get the problems sorted out. What we have listed here is one potential cause for this happening, but there could be others as well. It's really hard to say without knowing why the check engine light came on in the first place.


 If you do have a light that comes on and turns off then there's a good chance you have a situation where information is being interpreted by your car's computer as faulty at one moment and then correct at another moment. It's very likely that if the light turned on and then turned off it will probably turn on again sometime in the near future. Generally speaking, if something set the light off, it's not going to get repaired unless you do something to address it.


 Keep in mind however that there are simple reasons why the check engine light can turn off, the gas cap being loose is one of the best examples of this, and a simple tightening the next time you fill up your gas could fix the problem.



 Is It Safe to Drive with a Check Engine Light On?


 This is one of those questions that can have many different answers and unfortunately, we can't really narrow it down any further for you. To say it's safe to drive with the check engine light on is not something you can really do until you know why the check engine light came on in the first place. The nature of the issue that your vehicle is dealing with will determine just how serious that light really is.


For instance, your check engine light could turn on if your gas cap is loose. Obviously, that's not an incredibly serious problem and you can safely drive for probably several thousand miles with a loose gas cap, or at least from one fill up to the next. However, if you have a serious problem with your catalytic converter then you could be expelling some harmful fumes if you continue to drive without getting you check engine light addressed. Likewise, if it's a problem with the cooling system in your vehicle or your engine oil then you could be doing some serious damage to your car by not getting the engine checked to figure out why that light came on. So, until you really know why you have a check engine light on you can't say for sure whether or not it safe to continue driving for any amount of time with it on or not.


 It's for this reason that it's really not worth risking not getting your light checked when it does show up. Even though it can be a nuisance for many drivers, even though many drivers have probably put off getting the light checked out when it shows up and driving quite a long time without any serious repercussions, there's always the possibility that if you ignore it something catastrophically bad could happen to your car as a result that's going to see you spending a lot of money on repair bills.


What Could Set Off My Check Engine Light?


 As we said there are a number of causes, well into the hundreds in fact, that can cause your check engine light to go off. However, some are much more common than others. With that in mind, let's take a look at what are some of the most common reasons for your check engine light to come on to help narrow down the range of potential problems you might be dealing with.


Loose Gas Cap: If the check engine light has come on right after you stop at the gas station to fill up, this should be the first thing that you check out. Take the gas cap off and then put it back on again as securely as you can. Start your car and see if the light is still on.


Bad Oxygen Sensor: Your car probably has at least two oxygen sensors that it relies  on to help determine how efficiently your car is burning fuel. If any one of these oxygen sensors were to fail it would trip the check engine light. It's good to get the check engine light looked into if this is the problem because if your O2 sensors aren't working you're going to suffer some bad gas mileage as a result.  If it's left to go for too long, then you may also suffer some problems with your catalytic converter as well.


Bad Spark Plugs: If your spark plugs or your ignition coils aren't working correctly then you're not going to be producing the combustion reaction necessary to keep your engine running properly. This can result in engine misfires which greatly reduces the power output from your engine and will also cause your check engine light to come on as a result.


Bad Catalytic Converter: The catalytic converter in your vehicle is important for reducing harmful emissions from your exhaust. When it fails not only will you be releasing more dangerous emissions, but you're also going to fail your emissions test as a result. And your check engine light is going to go off to warn you that it's a problem.


Bad Mass Air Flow Sensor: The mass airflow sensor is necessary for tracking the air that comes into your engine so that your computer is able to maintain the correct air to fuel ratio in the combustion chamber. When the mass airflow sensor isn't working properly you can't burn the right air to fuel ratio and your gas mileage will suffer.


Bad EGR Valve: The exhaust gas recirculation valve takes some of your exhaust fumes and recirculates them back into the engine to help lower the temperature overall which in turn reduces dangerous levels of chemicals that your engine could be producing otherwise at higher temperatures. If the valve isn't working the way it's supposed to it's going to trip your check engine light. Sometimes that means you'll need to replace the valve, but it's also possible it could just use a good cleaning to get back into proper working order. 


Vacuum Leak: Several of the systems in your car are probably controlled by a vacuum system. Unfortunately, the vacuum hoses only have a limited lifespan and overtime will crack causing leaks. If you live in a colder climate, they will probably wear out much sooner than they will elsewhere because of the temperature extremes between summer and winter. When your vacuum system springs a leak it's going to set off a check engine light on you. 


Bad Thermostat: The thermostat in your engine regulates the flow of coolant. Occasionally your thermostat can get clogs and it will either be stuck in the open position so that the coolant is flowing constantly or the closed position so that no coolant is flowing. Closed is more dangerous for your engine but neither one is good and both can cause your check engine light to go on.


Bad Car Alarm: If you've installed an aftermarket car alarm in your vehicle it could be causing some serious trouble. Not only can it drain the battery, but it can also trigger a check engine light and potentially shut down your car and stop it from starting altogether. It's going to be the result of a poor installation and incorrect wiring. 


Bad Battery: The average car battery only has a lifespan of about 3 years to 5 years. After that amount of time it's going to have a significantly reduced charge and may not be able to properly power your vehicle when you're trying to get it started. Eventually it will not work at all and you'll have to replace it with a new one. In the interim however a battery with a bad enough charge can cause your check engine light to go off.


 The Bottom Line


Even though check engine lights are notoriously easy to ignore and many drivers will go out of their way to even cover them up so they don't have to look at them, you really need to get to the bottom of why they've come on in the first place to know whether or not you need to worry about it. While it's possible that it may not be a big deal as in the case of our gas cap example, it could also be something potentially very  problematic, like an issue with your catalytic converter which could end up costing you well over $1,000 to repair. The best thing you can do when your check engine light comes on, even if it goes off again shortly thereafter, is to take your car into a mechanic to get it checked out or to invest in your own OBD2 scanner to get to the root of the problem.