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What Your Check Engine Light Means | Flashing, Solid, or On & Off

Usually, check engine lights either blink or are constantly illuminated. Sometimes, they go on & off (intermittent problems). Driving with a solid light MAY BE OK if you know the cause. Do not drive with a blinking or flashing light, even if it’s only flashing sometimes, serious engine damage is possible.

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Your check engine light, sometimes called the malfunction indicator lamp (MIL), means that your car is experiencing an engine problem. Depending on the vehicle, the warning could also include words such as “Check” or “Service Engine.”

Check Engine Lights (CELs) are triggered when one of the engine’s systems is experiencing an issue. It is used to notify the driver that something isn’t functioning the way it should. However, the light alone isn’t the whole story. It’s actually the diagnostic trouble codes (DTCs) that triggered the check engine light that are used to narrow down what the issue is. 

DTCs are the onboard diagnostic system’s way of telling you something’s wrong with a specific engine system. These codes are what technicians and mechanics check your vehicle for when you take it to the shop

DTCs are accessed through your vehicle’s onboard diagnostic (OBD) port. This port connects to your car’s OBD system, a computer system that monitors and regulates vehicle performance or, when something goes wrong, reports DTCs. All vehicles sold in the U.S. since 1996 use the OBD2 (OBD ii) system. 

Although serious engine problems do happen, the problem causing your light could be an easy fix. Perhaps it’s just a loose fuel cap. Or, an illuminated oil pressure light indicating something as simple as your car needing its oil topped off. So don’t freak out just yet.

Still, the issue could involve one of several do-not-drive conditions, like a faulty catalytic converter, a leak in the engine, overheating, or faulty internal engine components.

This article focuses on your check engine light’s meaning and guides you through deciding whether or not you should drive with your check engine light on. Along the way we’ll point out a few resources for diagnosing your light too. If you already know what information you are looking for, here are some quick links to our more hands on content about check engine lights:

      1. What to Do When Your Check Engine Light Comes On
      2. Can You Drive With The Check Engine Light On?
      3. The 13 Most Common Reasons For A Check Engine Light | How To Diagnose Them
      4. How to Read a Check Engine Light With or Without a Scanner
      5. Where To Get Your Check Engine Light Checked For Free
      6. How to Reset Your Check Engine Light | 4 Ways To Clear It (With or Without a Scanner)

    FIXD has scanned millions of cars and we’ve used this information to narrow down the most common possible causes for check engine lights. The article below gives you everything you need to know about your light in plain english.

    Let’s dive in.

    How Serious is a Check Engine Light?

    There are a couple of indicators to pay attention to when your light comes on that can help you gauge how serious the problem is. The most common indicator is whether it’s a solid check engine light versus a flashing one. 

    Alternatively, in some cars, the color of your check engine light may indicate the severity of the issue.

    What Does the Check Engine Light Look Like?


    A new driver or someone lucky enough to never have had car troubles may be curious about what a check engine light looks like. 


    Commonly it's an outline of an engine that will illuminate in red, orange, or yellow when trouble arises. 


    This check engine light logo may also be accompanied by the words “check engine,” “check,” or “service”. 


    The light may appear as a solid light or a flashing one (blinking like a turn signal). 


    Depending on the issue, the check engine light may also stay on constantly, or, turn on for a while & then off again.


    Special note: Some newer cars have a small digital screen that displays a check engine warning instead of the typical dashboard light.

    Check Engine Light Colors & Issue Severity

    Understanding check engine light colors comes down to knowing your car. In some vehicles, a yellow check engine light could mean a moderate problem, while a red check engine light indicates something severe. 


    Many cars only have an orange check engine light that may flash when there’s a significant issue. 


    Read the vehicle’s owner’s manual to become familiar with how the check engine light works in your car. 


    Most times you can find your owner's manual online for free by searching “{year} {make} {model} owners manual” in Google. Ex: “2022 Honda Civic Owner’s Manual”

    What Does a Flashing or Blinking Check Engine Light Mean?

    If you see your check engine light flashing it’s a warning that something is seriously wrong with the engine. Pull over (safely) and turn off the vehicle. Driving any further is likely to cause significant engine damage. A flashing light indicates a problem that needs immediate attention. Just get your car towed instead of driving.

    If a flashing or blinking check engine light were a person, it would be someone frantically waving and jumping up and down to get your attention.  

    If your light flashes, it will typically flash or “blink” at about the same rate as your car’s turn signal.

    How do you fix a blinking check engine light?

    is found by diagnosing the issue causing your engine troubles. Check out our article on the most common causes of a check engine light and how to diagnose them.

    Why is my check engine light blinking on and off intermittently?

    In some cases you may only see your check engine light flashing occasionally.


    Many causes of a flashing check engine light will make the light blink until the problem is fixed. So, it's understandable to be a bit perplexed if your “typical” flashing check engine light then stops all of the sudden. This, my friend, is an intermittent light.


    An intermittent flashing check engine light occurs when your engine has a serious but intermittent problem.


    Engine misfires are a common cause of an occasional flashing CEL; a spark plug or spark wire could be in the early stages of failure. Or, a blockage in the cooling system could suddenly cause the engine temperature to rise, only to have the bottleneck clear up on its own. 


    Whether or not the light flashes constantly or intermittently, it’s likely that driving your car will damage your engine. Just get your car towed instead.


    Take an intermittent flashing CEL just as seriously as a constantly flashing light. Problems can progress quickly.

    What Does A Solid Check Engine Light Mean?

    While less urgent than a flashing or blinking CEL, a solid check engine light indicates a non-emergency issue that requires prompt attention (within 1-2 days).

    Think of a less-frenzied person saying “This is critical; don’t ignore this problem.” 

    A steady or solid check engine light can still be significant, so it’s wise to still get it checked as soon as possible to rule out more serious problems that could damage your engine if driven.

    Keep in mind that a CEL doesn’t signal every possible vehicle issue and some symptoms can’t be detected by the OBD2 system. 

    You should still look into a vehicle that hesitates to start but has no check engine light, it won’t just fix itself. And just because the light isn’t on, it doesn’t mean you should ignore a weird sound coming from your engine compartment either. 

    Engine problems are often capable of damaging other engine components if left for too long. Being proactive about repairs will save you money in the long run. Use the FIXD Sensor and free app to find out why your check engine light is on, how serious it is, and what to do next so you can avoid expensive mechanic bills.

    Was your check engine light flashing then solid?

    Some might say “check engine light blinking then solid”, but, either way the answer is the same, it likely means you have a less severe but urgent problem. 


    The car’s computer (OBD system) may have “thought” it found a severe DTC but it resolved to a less severe one, turning the light from flashing to solid. Alternatively, this could also indicate an electrical problem or a faulty sensor. 


    Just like a solid check engine light that appears with no flashing beforehand, get it checked soon. You should be able to drive to a shop for service as long as no major issues were spotted when you went through our “What to Do When Your Check Engine Light Comes On” checklist. Also check out the section below about driving with a CEL on, we give you some tips on being careful.

    Why Does My Check Engine Light Go On And Off? (Intermittent Problem)

    A check engine light may appear and disappear a short time later if your engine has an intermittent issue.  When the light is on it may be solid or flashing depending on how serious the issue is.

    A flashing but intermittent check engine light:

    You have a severe but intermittent problem. Your vehicle should not be driven before the problem causing it has been repaired.

    A solid but intermittent check engine light:

    You have a less severe problem that is intermittent. Problems can get worse as time goes on but, driving your vehicle a short distance to a shop, home, or to get it scanned at an auto parts store should be possible.

    My Check Engine Light Came On Then Went Off. Are the codes still there?

    Most error codes are stored in the ECU. So whether you’re using the FIXD Sensor, another OBD2 code reader, or relying on a mechanic, the information on what’s causing the CEL should be there. Although your codes should stay in the ECU for a very long time, you should still check them ASAP. Your battery dying or disconnecting could clear the codes, or sometimes just multiple restarts of your car.

    If the check engine light went off by itself after diagnostic tests, the technician or mechanic may have cleared your light.

    An intermittent but solid-while-on check engine light may not seem to indicate the same priority as a solid light that’s constantly on but, it should still be looked at within a couple of days to rule out any serious engine problems. Often, an intermittent light may indicate an engine component is failing.

    In 10+ year old cars you may see a check engine light went off by itself only to turn back on shortly afterwards. This is often due to an oxygen sensor or catalytic converter that’s just starting to go bad. It might look something like this:  

    The check engine light went off after a week, then, a couple days later it’s on again, then off for a day. Now it’s flashing constantly.

    A light triggered by a failing converter, or oxygen sensor, will often switch on and off more and more frequently until, eventually, it’s constantly solid or constantly flashing. This would be when the oxygen sensor, catalytic converter, or both have entirely failed. 

    Waiting for complete part failure can damage other engine components and make your repair bill much larger than it had to be. Like a failing Oxygen sensor ($155 – $500 to replace) leading to a damaged catalytic converter ($2000 to replace). Don’t wait too long to fix intermittent issues, it’s not a free pass to keep driving, it’ll cost you later. 

    Can You Drive With The Check Engine Light On?

    If you’ve got a solid check engine light, you’re probably wondering if you can drive with check engine light problems still going on. 

    Let’s explore this.

    Is it safe to drive your car with the check engine light on?

    The most effective way to determine if it’s safe to drive your car with the check engine light on is to read your codes.

    While getting codes is always preferable, without the codes, you can still make some quick judgments based on your cars’ symptoms.

    We outline how to do a quick car check in What To Do When Your Check Engine Light Comes On in detail. 

    If you want a sneak peak, click on the sneak peak box right below for a quick 5-step synopsis on how to check for big issues and get to a shop or auto parts store quickly. 

    What to Do When Your Check Engine Light Comes On

    #1: Pull over and turn off the vehicle (where it’s safe).


    #2: If you notice anything unusual, such as elevated engine temperature, shaking, vibrations, an atypical noise, a burning smell, or loss of power, then the situation is severe enough that calling a tow truck is the right remedy. The same applies if the check engine light is flashing. 


    #3: Two Options:


      1. If there are no apparent serious issues, restart the car after waiting a few minutes. If the CEL is off now, then continue driving while being alert for any developing problems. Ideally, head to a mechanic or auto parts store to get it checked as soon as possible. 
      2. Alternatively, you can use an OBD2 reader like FIXD to diagnose the check engine light in seconds using your smartphone. FIXD also tells you how serious the problem is so you know if it’s safe to keep driving.


    #4: A CEL that remains on after restarting (or comes back on after a few minutes) means the problem hasn’t gone away. Driving to the repair shop could be the next step if you feel confident it isn’t a serious issue and the light is solid and not flashing. 


    If you do drive, drive carefully. Issues can always get worse.


      1. Turn off the stereo so you can hear your car and drive slowly
      2. Don’t get on the highway, and if you’re are on one, try to find a side road instead
      3. Stop driving and just get towed if:
        • Worrisome noises arise
        • Your check engine light is blinking and car is shaking or your check engine light is on and your car is shaking while accelerating. Any shaking or chugging means you should get towed.
        • You see your check engine light flashing under hard acceleration 
        • Your check engine light starts flashing at all, under any circumstances, even if its intermittent

    If you aren’t sure what the issue is with your car, don’t drive.

    Yes, getting towed is a hassle and can be expensive, but here’s why it’s so crucial.

    • Being towed prevents any engine damage from occurring. Driving even a short distance with an overheated engine, for instance, can lead to a cracked engine block or other catastrophic problems. It’s best not to take the risk.
    • Using a tow truck also prevents accidents. A car that stalls, misfires, or can’t accelerate can create a safety hazard while turning at an intersection or while merging, exiting, or otherwise driving on the highway. 

    How long can you drive with a check engine light on?

    If you’ve got a trip planned, it’s natural to ask if you can drive long distances with a check engine light on. As usual, the answer depends on the severity of the engine issue.

    Is your check engine light flashing?

    If so, you should definitely avoid any driving, no matter the distance.

    Is your check engine light solid?

    While solid lights are less severe than flashing lights, ignoring any check engine light and setting out on an all-day trip is a recipe for disaster. A minor problem can rapidly turn into something more severe over the course of a hundred miles.


    Try to avoid driving further than 50 miles with a solid check engine light. Get it fixed quickly.

    The best way to avoid getting stranded, if you choose to drive with a CEL, is to get the problem looked at before hitting the highway to make sure you won’t destroy your engine or cause an accident because of an engine malfunction. Even then, you are taking a risk, it’s usually best to get the issue fixed entirely before hitting the road, even if you think you know what’s causing it.

    13 Most Common Reasons Your Check Engine Light Is On

    Below is an overview, but you can read our article, The 13 Most Common Reasons For A Check Engine Light | How To Diagnose Them too. It covers symptoms, whether you can drive, and repair costs in more detail than the synopsis below.

    1. Loose Gas Cap

    A gas cap check engine light occurs when the cap hasn’t been properly secured after a fill-up (or if the cap is damaged). Keeping the cap tight limits the escape of harmful vapors into the atmosphere. In addition to a CEL or warning light, you may also notice the smell of gasoline near the gas cap door.


    The check engine light should turn off shortly after the cap is re-secured. There’s no serious risks to your engine by driving with this type of light on, but make sure to tighten your cap each time you fill up. A loose gas cap makes your car less fuel efficient and the evaporated fumes aren’t good for you or the environment either.

    2. Spark Plugs & Plug Wires

    Can spark plugs cause a check engine light to come on? Absolutely. A faulty spark plug or spark plug wire is likely to lead to misfires and poor acceleration. You may even notice a drop in fuel economy, engine knocking, rough idling, and a gas aroma coming from the tailpipe. 


    In extreme cases, malfunctioning spark plugs can damage the catalytic converter (expensive to replace) or cause a misfire leading to engine damage. 


    Your car is generally drivable with a spark plug-related issue, but remember that sluggish acceleration can be dangerous in some driving situations. Get the problem looked at right away. Stop driving and get towed if you notice misfires or a flashing check engine light.

    3. Low Oil & Low Oil Pressure

    Consider a low oil pressure check engine light to be a serious issue, and the same can be said of low oil. Insufficient engine lubrication can lead to significant engine damage. In addition to standard warning indicators, keep an eye out for unusual sounds coming from the engine or overheating. Other symptoms can include oil puddles under the car or a burning smell coming from the engine compartment.


    If your car’s low engine oil is the result of not checking the oil level in a while, then your issue may be less serious and adding more oil should fix the light. If it is anything other than an overdue oil top off, find a safe spot to park, turn off the car, and call a tow truck. You likely have a serious issue.

    4. O2 Sensor Failure

    An O2 sensor check engine light comes from a faulty component in your car’s pollution control system. The oxygen sensor (one of a few in most cars) monitors and adjusts emissions. When one gets damaged, there may be a drop in fuel economy, poor engine performance, failed emissions testing, and/or a sulfur smell coming from the exhaust system. 


    It’s fine to drive short distances with a faulty oxygen sensor, but continued operation under these conditions can damage the catalytic converter which is expensive to replace.

    5. Catalytic Converter

    10+ year old cars are especially likely to get a check engine light for catalytic converter issues but, it could happen to newer cars too. These pollution control devices wear out over time, and every modern car engine has one. When a catalytic converter breaks down, you’ll encounter sluggish acceleration, increased fuel consumption, smelly exhaust fumes, and more damaging emissions. 


    Driving with a troublesome catalytic converter is unlikely to destroy your engine, but the problem should be addressed as soon as possible. Remember, some states won’t let you renew registration if your car’s emissions are too high. A broken catalytic converter is a surefire way to fail a smog or emissions test.

    6. Mass Airflow Sensor

    The mass airflow (MAF) sensor measures the air-to-fuel ratio entering the engine to ensure smooth operation and optimal performance. While a bad MAF sensor can cause a check engine light, a bad mass air flow sensor with no check engine light can happen too. 


    When diagnosing a bad MAF sensor, be on alert for rough idling, stalling, and poor engine performance. Hard engine starting, reduced fuel economy, and the smell of gasoline in exhaust fumes are other indicators of a faulty MAF sensor. 


    You won’t make matters worse by driving with a bad MAF sensor most of the time, but a reluctant engine can make for hazardous operations. Don’t delay getting the MAF sensor repaired.


    Keep in mind that sometimes your MAF sensor just needs to be cleaned. Pick up a can of MAF sensor cleaner if it looks dirty to you. Also, check to see how dirty your air filter is. If it’s bad, clean or replace your air filter too.

    7. Overheating

    You should be concerned by your car overheating whether or not it comes along with a check engine light. Without proper cooling, an engine can be destroyed in minutes. Besides a warning light or a temperature gauge, signs of an overheated engine include lagging engine performance and steam or a burning smell coming from the engine compartment.


    At the first sign of overheating, pull into a safe spot and turn off the car. After the engine has cooled down, it may be OK to drive a very short distance to a repair shop (don’t drive if the coolant is empty). Otherwise, contact a tow truck for transportation. 


    If you are in a pinch and most or all of your car’s coolant has leaked out. Let the engine cool down and then add water to the radiator (you’ll need a few gallons). If it is a small leak, this will help you drive just a little further and get to a shop for service. Just make sure you drain any water once you get to the shop. In cold weather, water in the engine or radiator could freeze and damage the car.

    8. Transmission

    Will a check engine light come on for transmission problems? It depends on the issue and the vehicle, as some cars have a separate transmission warning light. However, transmission problems require immediate attention. Besides dashboard indicators, gearbox issues can be spotted by looking for a transmission fluid puddle under the car, a burning smell from the undercarriage (which can come into the interior), slow shifting, or a whining or grinding noise while the car is in motion. 


    Transmission issues tend to be complex (and expensive). Don’t make matters worse by driving to a mechanic, even if you make it, you may irreparably damage your transmission. Use a tow truck instead, you’ll probably save yourself a lot of money in the long run.

    9. Battery

    Dealing with a check engine light that’s on after a battery change should be uncommon. In this situation, you’re likely dealing with loose or damaged power cables or a faulty replacement battery (it happens sometimes). Signs of this type of problem range from an engine that’s hard to start, to a clicking sound while turning the ignition key. Corroded battery terminals and flickering headlights are indicators too. 


    Driving with a faulty battery won’t cause any damage, but there’s a chance of getting stranded.

    10. Vacuum Leak

    Will a vacuum leak cause a check engine light to appear on the dashboard? Yes. A car requires a pressurized fuel system, so a loose or cracked hose can upset that delicate balance. Common signs of a vacuum leak include sluggish acceleration, erratic idling, a dip in fuel economy, and a whistling sound in the engine compartment.


    Driving with a vacuum leak isn’t a big deal, but have it taken care of soon to reduce the extra stress on the engine.

    11. Exhaust Gas Recirculation Valve Failure

    Most car owners don’t give the exhaust gas recirculation (EGR) valve a second thought until it becomes faulty. This small component controls the recirculation of exhaust gasses, but it can become clogged or damaged over time. When this happens, a car will emit more nitrogen oxide, and the engine will be less efficient. 


    Typical symptoms of a bad EGR valve include stalling, engine knocking, reduced fuel economy, and exhaust fumes that smell like gasoline. In this condition, a car won’t pass an emissions test. You may be able to drive with a faulty EGR valve, but have it replaced right away to minimize damage to the catalytic converter (much more expensive to replace). 

    12. Check Engine Light Is On For No Reason Or Malfunctioning

    Can a check engine light come on for no reason? Definitely, yes. While modern cars are supposed to be precision machines that provide definitive reasons for malfunctions, something as simple as a loose wire or connector can cause a CEL to come on. 


    If the light is solid, be on alert for any unusual conditions, such as a sound, smell, or vibration that’s recently appeared. 


    If the light is flashing, skip driving and get help (even if you think it’s nothing). Calling a tow truck is the best way to minimize the risk of further damage.


    Even if it is just a wiring issue, get the false check engine light fixed soon. It would be a shame to have a real engine malfunction and miss it because the light was already on. Some CEL causes don’t take long to progress into engine failure. The earlier you catch a problem, the better.

    13. Failing Aftermarket Alarm

    Can a car alarm cause a check engine light to come on? In a word, yes. A cheap system or incorrect installation can cause voltage fluctuations and other electrical issues, which will trigger a CEL. 


    If you’re also dealing with a car that’s hard to start, problems locking and unlocking, and/or other electrical problems, an aftermarket alarm could be the culprit. Driving with a system that’s got bugs is usually fine for the engine but it can be a major inconvenience to the driver.

    Most Likely Check Engine Light Causes, Repairs & DTC Codes

    If you aren’t able to get your DTC codes or you just haven’t done it yet, it may be helpful to know the most common reasons for a CEL for your particular make and model.

    We’d also suggest taking a look at the full length article: The 13 Most Common Causes For A Check Engine Light | How To Diagnose Them.

    Based on FIXD app scans, we’ve compiled a list of the most common DTC codes for popular makes and models. Explore these articles to learn about the most common codes, their most common repairs, and their costs.

    Most Common Check Engine Light Codes & Repairs By Make & Model

    Most Common Check Engine Light Codes & Repairs By Make & Model

    How To Read A Check Engine Light

    If you’d like a full set of instructions for reading DTCs, check out: How to Read a Check Engine Light With or Without A Scanner

    FIXD And Other OBD2 Scanners

    An OBD2 scanner can easily tell you your engine’s diagnostic trouble codes by plugging into the OBD port and scanning the ECU (computer). But, once you’ve got the codes you’ll need to look up what each DTC code means, the possible causes, and then research how much the repairs will cost so that you are prepared to negotiate with the mechanic or price out the DIY solution. 

    But with FIXD, there’s a simpler way to diagnose your check engine light. The FIXD sensor scans for DTC codes and then reports on the problem with an easy-to-understand explanation right on your smartphone. We also include repair estimates, how-to guides to fix issues yourself, and recommendations for trustworthy repair shops in your local area. Our app helps you get more than just the code, it helps you understand the problem, how to fix it, and how not to get ripped off. It makes repairs less stressful and less time consuming.

    FIXD premium subscribers also have access to additional support through the FIXD Mechanic Hotline. If you give our sensor a try ($19.99) we will give you a 2-week free trial to premium. You’ll have access to unbiased advice about car repairs and maintenance from a pro mechanic. 

    Where To Get Your Check Engine Light Checked

    Not everyone has access to the FIXD app or an OBD 2 scanner; not to worry. There are many places to get your engine light checked. Even for free.

    Who can check an engine light for free?

    We found 6 national chains that will check your engine light for free. 3 national auto parts store chains: AutoZone, Advance Auto Parts, and O’Reilly Auto Parts. And, 3 national repair shop chains: PepBoys, Firestone, & Goodyear. 

    Local mechanics may provide the same service too so feel free to shop local if you prefer. 

    Rent An OBD2 Scanner

    For those in need of a more comprehensive scanner, you can rent an OBD2 scanner at AutoZone or many other auto supply stores. These advanced devices are best left in the hands of experienced mechanics. 

    Unless you’re an experienced DIYer that absolutely needs an advanced scanner for a very specific task, save your money. Most times a rather basic OBD2 scanner will get you the answer you’re looking for, you don’t need to drop a lot of money on an advanced reader to find the solution.

    How to Clear A Check Engine Light From Your Dashboard

    Learning how to reset the check engine light is a straightforward task; there are several options. Here’s a summary of the different approaches. 

    Important: Resetting your engine light by disconnecting the battery is risky in some newer cars because of their computers. Read our article on how to turn off the check engine light for the full pros and cons of each technique before attempting any of them.

    How to reset a check engine light - 4 options:

    • Use the FIXD app or an OBD2 reader to quickly clear most active DTC codes (keep in mind that the code will reappear if the problem hasn’t been fixed).


    • Turn the engine on and off three times in a row. (Some codes may need to be cleared with a device.)


    • Drive. A code will usually clear on its own after the problem has been fixed. Note that it may take several separate trips and many miles for this to occur, and some codes will still need to be cleared with a device. 


    • Disconnect and reconnect the car battery. This is a last-resort method that should be used sparingly as you’ll wipe out stored settings like radio presets and seat memory positions. Such steps could also involve having to re-enter the unique radio ID and having the dealer reprogram the ECU (expensive). 

    Turning Off The Check Engine Light Without Fixing Your Car (Don’t Just Ignore It)

    It can be tempting to reset a check engine light without completing any corrections. But ignoring a problem won’t make it go away. In fact, you’re likely to make things more complicated. For instance, clearing a CEL that was caused by your engine overheating and continuing to drive is a guarantee of expensive repairs ahead. An overheated engine can turn into a cracked engine block, and engines can cost thousands of dollars to replace.

    Will The Check Engine Light Go Off By Itself?

    In order for the CEL to go off by itself, the condition triggering the light in the first place must no longer be present. This may come from a temporary problem (like a clogged MAF sensor that clears up) or a repair that corrects the issue. 

    Does the check engine light turn off automatically after a repair?

    Will a check engine light go off by itself? Generally, a properly performed repair will resolve the problem that triggered the check engine light to come on. The CEL should go away right away or after a few driving cycles. Sometimes, the trouble code may need to be cleared by the FIXD app or OBD2 reader.

    How long before the check engine light goes off after the gas cap has been tightened?

    A CEL resulting from a loose gas cap is a very common issue. Retightening the cap usually clears the check engine light nearly right away. However, it can take as much as 25-30 miles for the CEL to go away sometimes.

    Can you clear a check engine light?

    You can clear a check engine light.. The easiest way to clear a light is with the FIXD app or an OBD2 code reader. There are alternative techniques, too. We cover these in a separate, more detailed article: how to reset a check engine light.

    How long does a check engine light stay on?

    A check engine light will stay on or come on intermittently until the issue triggering the light is resolved.

    Frequently Asked Questions:

    Can I Rent A Check Engine Light Reader?

    Yes, AutoZone and other auto parts stores offer OBD2 scanner rental services for advanced devices (less advanced devices are usually lent out for free).

    Can I Take An Emissions Test With An Illuminated Check Engine Light?

    It’s a smart idea to fix what’s causing the CEL before having a car’s emissions checked. If the issue involves the pollution control system, then the car would fail the testing. 


    Because modern vehicles have so many interconnected systems, even something as seemingly minor as a clogged mass airflow (MAF) sensor could impact an emissions test. 


    The emissions/exhaust system is a frequent cause of check engine lights and can cause a car to fail an emissions test quite easily. Don’t waste your time and money, get it fixed first.

    What Does The Service Engine Soon Light Mean?

    I can hear the confusion – Why is my service engine soon light on? Is it the same as a check engine light?


    A solid “service engine soon” light does not indicate a problem like a solid check engine light does, it typically indicates scheduled maintenance. It’s a reminder to bring your car in for repairs and/or maintenance in the very near future (days or weeks). The message is usually triggered after you’ve driven a certain number of miles or if a set time period has elapsed. 


    Ok but, why is my service engine soon light blinking?” 


    You need to take your car in for service immediately, your car is overdue for maintenance (blinking or flashing means urgency). 

    What Is The Most Common Reason For A Check Engine Light?

    There can be hundreds (if not thousands) of reasons for a check engine light to come on. However, the reason is usually related to emissions, like an oxygen sensor or MAF sensor. Pollution control systems are highly sensitive, and the slightest variation beyond a normal operating condition can trigger a CEL.

    Does The Check Engine Light Always Mean That There Are Issues?

    A check engine light indicates the system has detected a DTC code, signaling there’s some type of issue with your engine. While there could be a problem with the diagnostic system itself and not the engine, that is extremely rare. Remember though, just because your engine has an issue doesn’t mean it’s serious, get it checked out. You may find it was just a loose gas cap.

    What Does It Mean If My Check Engine Light Turns On And Off?

    An intermittent CEL shows that the problem comes and goes. It’s not an unusual situation and can happen, for example, with fluctuating voltage or a periodic blockage of a sensor. An intermittent light is different from a flashing CEL. A flashing light signals a significant issue requiring you to stop driving, turn off the car, and call a tow truck. Read our section on the meaning of flashing check engine lights for more information, we break down the differences between a solid check engine light vs flashing vs intermittent.

    How Often Does A Check Engine Light Indicate Serious Problems?

    There’s no precise formula that details how serious a CEL is. But, know that a flashing check engine light is a sign of a significant problem (meaning don’t drive any further). However, a CEL doesn’t have to flash to warn of a major issue. For instance, a check engine light accompanied by an unusual sound, smell, or vibration is an excellent indicator that it’s time to pull over and get a tow.

    If The Check Engine Light Is Off, Does That Mean Your Car Is Fine?

    A check engine is an indicator of detectable issues among monitored engine systems but, some engine issues aren’t detectable by the OBD2 system. Also, not every component in a car is monitored. For example, problems with the suspension won’t appear as a check engine light.

    Why Would A Check Engine Light Suddenly Disappear?

    There can be several reasons why a CEL abruptly turns off. The problem may have permanently or temporarily gone away. Or, the code got cleared after several drive cycles (this also means the problem is no longer detectable).

    Do Check Engine Light Codes Get Stored In The ECU If The Check Engine Light Turns Off On Its Own?

    Yes. The once-active DTC codes are stored for a mechanic to reference during the diagnostic test process. Stored codes can be cleared with the FIXD app or an OBD2 reader if the problem has been fixed.

    Should a check engine light come on when the key is turned?

    It’s normal to see a check engine light flashing when the key is in the on position or for it to be flashing before starting in general. The light appears solid or blinking, then goes off once the engine is running. A check engine light is only a problem if it’s on when the engine is running.

    David Goldberg

    Dave Goldberg is an automotive journalist and lifelong car fanatic. He writes for numerous enthusiast and business outlets and is an ongoing contributor to HotCars.com, one of the most popular car culture websites. When he’s not writing or driving, Dave is either under a hood or asleep. His credentials include a BA in Journalism from The George Washington University.

    Clear your check engine light in seconds

    The FIXD Sensor and free app tells you why your check engine light is on in easy-to-understand terms and lets you clear it with the touch of a button. 


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    About the Author

    David Goldberg

    David Goldberg

    Dave Goldberg is an automotive journalist and lifelong car fanatic. He writes for numerous enthusiast and business outlets and is an ongoing contributor to HotCars.com, one of the most popular car culture websites. When he’s not writing or driving, Dave is either under a hood or asleep. His credentials include a BA in Journalism from The George Washington University.

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