By on September 30, 2021

virgmos/Shutterstock.com

I was running an errand Sunday in a Mercedes S-Class tester when all of a sudden I saw the “check engine” light had popped on.

“Huh, that’s odd,” I thought to myself. Especially since the car was running and driving just fine.

Indeed, the next morning, the light was off.

I checked with the press fleet and I was told the dealer did a remote scan (I didn’t even know this was a thing) and found the car needed a software update. So, no big deal.

But I have to wonder — what’s the point of the check-engine light (CEL) if it doesn’t tell me, the driver, much about what’s wrong. I had no idea if there was an issue with the emissions components or the on-board diagnostics, or if the gas cap hadn’t been tightened by the previous driver (I hadn’t put fuel in the car or otherwise accessed the cap). All I knew is there was either something wrong or the computer thought there was something wrong, yet the car was experiencing no obvious drivability issues.

We need a better system. I am just not sure what.

Certainly, having error messages with specific problems pop up would confuse the general public. Most drivers don’t know a spark plug from a plug wire, and you can’t really expect the average driver to read an error message on the dash and know when to go to the dealer and when not to.

But on the other hand, many drivers do dash to the dealership the second the check engine light pops on, even if they end up finding they simply didn’t tighten the gas cap. Other folks, usually those who are driving older cars that are well beyond warranty, ignore the CEL because either they can’t afford extensive repairs and/or they’ve taken the car in before only to find the issue was minor and not worth spending money on.

The current system is set up so that if your CEL is on, you generally need someone with a scan tool to plug in and find out what the error is (or, I guess, you can get a software update). Sure, scan tools aren’t the exclusive domain of professional techs, but no matter who is wielding it, one is needed to figure out why the light is on.

I’ve never bought into the idea that the CEL is so nonspecific because the OEMs want you to spend money on diagnostic fees instead of fixing issues yourself. That’s because if it’s a customer pay job, the money spent on labor is going to the dealer, not the OEM, and if it’s a warranty job, it’s going to cost the OEM money. Not to mention consumers sometimes choose independent shops.

But I do find it quite annoying that the CEL can pop on, and I, the driver, have no idea why. Not knowing how much I need to worry is something that gives me anxiety.

Yeah, I know, we all hate the guy who points out an obvious problem without a proposed solution. And sorry, I got nothin’. All I know is there has to be a better way.

[Image: virgmos/Shutterstock.com]

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92 Comments on “Opinion: The Check-Engine Light is Useless...”


  • avatar
    jmo2

    You should be able to get the codes without a scan tool.

    But at least you can and with the code it will often tell you what’s wrong and Google will link you to the part you need and a YouTube video walking you though by step how to replace it.

    • 0 avatar
      Tim Healey

      True, I know some cars don’t require a tool. And I know older cars, you could use a paper clip to get it to flash. My point is just more general — what good is an error message light that’s so vague and can cover failure as minor as a loose gas cap and as major as “pull over and call a tow now”?

      • 0 avatar
        Kyree

        Right. Those’d be cars with pre-OBD 2 systems. You used a paperclip to jump some contacts, and then counted the light flashes to get a trouble code. However, that system is still cumbersome and–especially in a world where *every* car now has a pixel-based screen somewhere in the interior–extremely unnecessary.

      • 0 avatar
        sgeffe

        If the ECU detects a misfire, it’ll flash the MIL. And some cars can distinguish a gas cap and flash a message.

        It would be nice if you could access some sort of on-board system that could at least give you the codes, along with a “plain-English” explanation, then allow you to reset things, without needing a scan tool. Perhaps after doing that, the code data could be stored someplace until a scan tool does a “full reset” of the system (or if the battery is pulled).

        The bigger issue is when the battery voltage drops enough that all the nanny systems lose comms, and the dash turns into Times Square with warnings. Just flash a low-voltage message, or “possible charging issue,” and give the driver a way to reset that without having to visit the dealer.

        And yes, I should be able to swap out a battery in the parking lot of my auto parts emporium without having to use some sort of electronic device to make the car happy! (Looking at you, BMW!) Pull old battery out, hook new one up, reset radio presets, done! All the nannies should work immediately, and the emissions should be ready for testing after a couple drives of a few miles.

  • avatar
    RamblerAmerican

    We now have on-board computers in our cars that can do just about anything, including parallel parking and driving the vehicle, but these amazing computers can’t display in plain English why the check engine light has gone on. This can be very inconvenient, especially if you are driving in remote regions of the country, far from a car dealer, auto service center, or auto parts store. I purchased an OBD reader just in case the check engine light went on when traveling through remote areas of North Dakota and Montana during a recent cross-country trip. The information I can get from the OBD reader should be readily displayable without needing to carry a portable scanner.

    • 0 avatar
      Land Ark

      This is the correct thought.

      Certainly one of the 4 screens in the car can display the issue. The car can tell you when a door is open, the parking brake is on, the keys were left in the ignition/in the car, the brake needs to be depressed to shift out of park, the trunk is open, it’s time for an oil change, the windshield wiper fluid is low, it’s below 37 degrees so there may be ice on the road, one of your tires needs air, the coolant temperature is too high, and when stability control is activated but it won’t tell you that the MAF sensor isn’t getting enough current or cylinder 2 is lean? Well, the data is sitting there, the car knows exactly what’s wrong, why can’t it tell you?

      We know why.

      • 0 avatar
        Average Simp

        The reason why is most people are far to ignorant to use thier vehicles screen to pull trouble codes. A 10 dollar dongle and a free app is are the only things needed for basic diagnostics.

        • 0 avatar
          Lie2me

          This is the right answer. A little bit of knowledge can be dangerous. Most people have no idea how their cars run, if suddenly an error code flashes that’s more complicated then “Door Ajar” the average driver wouldn’t know what to do. These people need to go to someone who can diagnose the problem.

          For the rest of us with a little bit of car knowledge a $20 scanner and a quick google search will tell us if our cars are in serious trouble or just had a minor fart

          • 0 avatar
            sgeffe

            There’s people who will insist that the door is in fact a DOOR! Not a jar! (At least that’s what folks with the Chrysler Voice Alert systems did! :-D )

      • 0 avatar
        thegamper

        Right, average car sells for close to $40k, they cant incorporate $30.00 worth of technology you could find at PepBoys?

        On the other hand, if the codes pop up with mysterious descriptions like “PC Load Letter” or something, it may do more harm that good.

        I am not a coder, engineer, or mechanic…..but seems all the elements are there, cheap and could fairly easily be incorporated into a vehicle. It would be better then the nebulous CEL.

    • 0 avatar
      MrIcky

      Yes! What is the point of a center gauge oled display if it can’t simply say check Engine, the code number, and the short description. It seems to be something that can easily be done and now there’s plenty of screen real estate.

  • avatar
    ToolGuy

    Based on my limited understanding, flashing CEL is worse than steady on.

    [@Tim, with my 1995 GMT400 (missed OBD-II by one model year), to read the (much more limited) codes, you use a bent paperclip to short between two terminals and the truck flashes the codes at you, morse code style. Would you prefer that? I don’t.]

    https://repairpal.com/gm-obd-i-code-chart

    OBD-II rocks, and you don’t have to wait for a check engine light to get extremely useful information from the vehicle. I have started doing an engine scanner ‘check-in’ with my kids’ vehicles (check fuel trims, look at oxygen sensor ‘switching’ patterns, check misfire counts, evaluate engine vacuum, etc.) when they visit – since they now live 100 miles away [and I strongly prefer doing any repairs on my own schedule and in my own driveway].

    Scanner is also useful when looking at used vehicles (did you know the engine computer keeps track of how long it has been since a trouble code was reset?).

    • 0 avatar
      Tim Healey

      I’ve done the paper cip thing on a 90s Sierra.

    • 0 avatar
      Kyree

      Yes. Usually, a flashing CEL indicates an active misfire, meaning one or more of your cylinders isn’t fully–or at all–combusting.

    • 0 avatar
      dukeisduke

      Yes, a flashing CEL is worse, because it usually indicates an active misfire. An active misfire left unattended can lead to bigger problems – unburned fuel from a cylinder not firing ends up in the catalytic converter, which can overheat and destroy it, which will eventually trigger a P0420 (catalyst efficiency error). Big bucks.

  • avatar
    Cicero

    The biggest problem with a check engine light is that many drivers don’t know what it’s supposed to be. Replace it with a $$$ icon and it will make a lot more sense.

  • avatar
    IH_Fever

    You could have it tell you what’s wrong, but the average person wouldn’t know what to do anyway. Check engine seems to work ok for the masses. It would be nice if you didn’t need a scanner to see what the deal was though. Light comes on, you click the screen, it tells you that you forgot to fill the blinker fluid or the kanuter valve has failed. Disregard or freak out and head to mechanic, your prerogative :)

    • 0 avatar
      aja8888

      CEL only comes on for emission related faults. Low washer fluid, tire air low, etc have their own indicators.

      • 0 avatar
        jmo2

        But just to be clear “emission related” would include things like a bad spark plug or ignition wire causing a misfire this dumping unburnt fuel into the catalytic converter. That’s something that needs to dealt with ASAP.

        • 0 avatar
          Nick_515

          I bought my e91 BMW with a CEL two years ago. “Small evap leak” code, very common. I spent two and a half bringing the car back to spec – all agreed with the seller – but my mechanic simply will not bother with the code. I have a bluetooth code reader and Torque Pro just to make sure no other codes are ALSO being triggered while the stupid CEL stays on for the known (non-)issue.

          The Torque Pro was able to erase codes in the past, no more. Anybody knows what else is out there that can do it?

          • 0 avatar
            28-Cars-Later

            I don’t know what Torque Pro is but if it can no longer clear codes perhaps your mechanic’s code reader also cannot?

          • 0 avatar
            Scoutdude

            And that is exactly why they won’t tell you what the problem is. Many more people will ignore something like a small evap leak if they new what it was.

          • 0 avatar
            TheFirehawkGuy

            Apparently EVAP codes are hard to diagnose. If you study up on “mode 6” and get an app that can read those values for you, then you can get a better picture of what’s happening in the EVAP system. Between that and a smoke test of the lines you can probably get to the bottom of it.

          • 0 avatar
            SPPPP

            Nick_515, If the EVAP leak is actually fixed, I believe the code should clear on its own after a certain number of drive and park cycles without the fault. EVAP codes can take a while to clear because the car has to be parked and cooling down for the evaporation portion to be tested. But two years later? That means there’s probably still a fault there.

            While the EVAP code points you in the right direction, finding the exact location of the fault is likely something that you will have to diagnose old-school style, with critical thinking and simple tools. Take a bike pump and a bung and see if you can build up and hold a few PSI of pressure in the fuel system, through the filler neck. If not, there is definitely a leak in the EVAP system.

    • 0 avatar
      aja8888

      CEL only comes on for emission related faults. Low washer fluid, tire air low, etc have their own indicators.

  • avatar
    28-Cars-Later

    Its a catch all originally intended for components which defied worship of the almighty ManBearPig. Any actual drivability or safety issues are not relevant, it should really be a “$” sign because that’s what it really means: you will pay to or remedy this yourself prole.

  • avatar
    mcs

    There is an option. There are new car models for sale that don’t have CEL lights.

    • 0 avatar
      28-Cars-Later

      Nope but they will have an alert for “5% battery life, pull over now”!

      • 0 avatar
        jmo2

        But it’s not a surprise.

      • 0 avatar
        mcs

        @28-Cars-Later: “Nope but they will have an alert for “5% battery life, pull over now”!”

        Actually, they have exactly that, but you get directed to a charging station. But, ICE cars have the same thing. A low fuel light.

        • 0 avatar
          28-Cars-Later

          You may have access to the data that I don’t but batteries lose charge over time. While gasoline also degrades, it takes multiple months and it still can be burned. I can leave one of my cars parked for two weeks and the amount of gas stays the same, if I leave my hypothetical Leaf parked for the same amount of time how much of the charge degrades in that period? How about in winter vs summer? I don’t want to fart around with that stuff and the nuances of constant charging like a computer, a HSD hybrid would do fine as a DD.

          • 0 avatar
            dal20402

            I have actually left my Bolt parked for two weeks on a couple of occasions, once in mild weather and once in cold weather. In that time it lost a percent or two of charge.

            You can avoid any loss at all by leaving it plugged in. If plugged in, it will stop charging when full and then start charging again when it loses a couple of percent.

          • 0 avatar
            28-Cars-Later

            @dal

            Thanks, I imagined it worked like a laptop or a phone. Given my steep driveway, I generally don’t park inside during the winter so running a 120 or 240 line up the side of the driveway to the top and then leaving something plugged in all winter in -5 degree to 30 degrees in Jan/Feb doesn’t appeal to me at all. I bought the IM because I read it did well in the snow and the Prius did not, but I believe the latest one has partial AWD as an option and if that was available in 2018 I would have been satisfied with a Prius for a DD. I don’t want to be tethered to anything, let alone on a nightly basis.

          • 0 avatar
            SCE to AUX

            @28:

            Vampire losses in a battery seem to be Tesla’s domain – sentry mode (security camera recording) is very power hungry, for example.

            But my former 12 Leaf and current 19 Ioniq don’t lose much if anything when parked for a few days, even in the cold.

          • 0 avatar
            28-Cars-Later

            @SCE

            That’s a good point about additional car electronics being an issue of additional drain whether in park or while driving. I’m sure somewhere its being kept track of but if designs/battery families have similar product cycles to current models software and O/S changes could use more energy than the original hardware was spec’d for. Similar to how older laptops with new factory batteries drain differently with newer operating systems/newer software versions.

            Since Tesla is the leader I imagine eventually the other marques will adopt some of its techniques or similar technology and they all will have a mild power drag at some point.

    • 0 avatar
      ajla

      I wish BEVs came with a “real range” display option. Tesla especially bakes in way too much safety margin. When my IP says 0% I want it to be dead.

      • 0 avatar
        SCE to AUX

        They are getting better. My Ioniq has a pretty accurate battery gas gauge. I ran it down to turtle mode twice and the display was blank when it happened. That was harrowing.

        From what I’ve read, turtle mode means you’re down to about a mile or two left, and I drove it about 3/4 mile that way.

        For a variety of technical reasons, lithium ion battery gas gauging is very difficult to do. It’s amazing that it is this good.

      • 0 avatar
        jack4x

        “When my IP say 0% I want it to be dead”

        Isn’t the reason they don’t do this because it’s harmful to the battery to regularly run down close to 0%? Easier to make people think they are running out of juice when there’s 10% left in the pack than to educate them on proper charging procedure for max life.

        • 0 avatar
          mcs

          @jack4x: It depends on the battery chemistry and the manufacturer. There’s no hard percentage number. On some of the next generation chemistries, like CATL’s sodium-ion, they don’t even need battery management and you can run down to 0% all you want. But, with current lithium-ion, it would be a pain to try to remember what the proper low percentage for your particular battery is if you had multiple cars with different optimal low charge points.

          In my own experience, in seven years of EV driving I’ve only been under 10% indicated charge maybe 3 times. Now that I mostly telecommute, I’m only using a couple of kilowatts each trip.

      • 0 avatar
        Lou_BC

        “Vampire losses in a battery seem to be Tesla’s domain”

        That must be from all the spying Tesla does for the USA Government with those “peripheral” camera’s.

        “Report: Chinese Military Bans Tesla Vehicles From Facilities By Matt Posky on March 19, 2021”

  • avatar
    northeaster

    As a former B5 Passat owner, I have previously experienced a long, warm and fuzzy relationship with said item.

    I kind of miss it.

  • avatar
    Secret Hi5

    I propose an annual subscription that allows the manufacturer to monitor your vehicle and informs you of problems. Bonus 10% discount if you bring the vehicle to the authorized dealer for service. :p

  • avatar
    jkross22

    My CEL is smart. It can glow yellow or red. Yellow means you’re screwed. Red means you got screwed 100 miles ago.

    Mine alternates between yellow and not on at all. I heard it’s either a bad gas cap, the weather (which it might be!), a sensor in the gas tank or a sensor in the engine.

    No one can explain why it sometimes glows and sometimes doesn’t. It’s such a tease.

  • avatar
    mor2bz

    A bit of tape over the light will fix it.

    If it is one for a couple weeks, then off, I don’t worry about it.

  • avatar
    Gardiner Westbound

    “That’s because if it’s a customer pay job, the money spent on labor is going to the dealer, not the OEM, and if it’s a warranty job, it’s going to cost the OEM money.”

    Manufacturers pay much less than retail rates for warranty repairs. They join forces with dealers to deny warranty claims, place blame on customers and withhold fixes. Notwithstanding Internet owner forums filled with similar complaints the dealer may say the problem is normal, he can’t replicate it, nobody else has complained, or band-aid it until the warranty matures, then magically discover the solution and demand payment.

    • 0 avatar
      DenverMike

      Dealers are the biggest criminals in the industry, followed by automakers. I would buy it without a warranty with enough taken off the top. They’ve had to put out zero dollars into the last five new vehicles I’ve purchased due to my normal care, buying right, fix myself or ignore minor problems, or warranty claim denials. I’d rather them not ever put their hands on it after the sale.

    • 0 avatar
      PeriSoft

      “Manufacturers pay much less than retail rates for warranty repairs. They join forces with dealers to deny warranty claims, place blame on customers and withhold fixes”

      I keep hearing this, and especially about Hyundai, but I’ve owned a Sonata and a Genesis and have not *once* encountered pushback on warranty repairs, even nebulous ones. Right now I’m in a free loaner while Hyundai waits to be able to make an ECU for my Genesis, and they’re covering 90% of the multi-K bill even though the car was way out of warranty when the problem hit.

      Perhaps I’m just extremely charming.

  • avatar
    Kendahl

    I was told that a flashing CEL was more serious than one that was on steady. The CEL in my 1998 Subaru turned on quite frequently. Each time, the fault was low catalytic converter efficiency on bank one. That wasn’t surprising since the car was getting old.

    The independent shop I patronized read and cleared the faults for me a couple of times and then suggested that I get my own reader to do it myself. That worked for the rest of the Subaru’s life. I still have the reader and now use it on my 14-year-old Infiniti which is beginning to throw the same code.

  • avatar
    carcomment

    Great article. The real story is just glossed over…the dealer remotely accessed the vehicle. That should strike terror in people’s hearts and minds. Is this limited to press vehicles or can they do this to any vehicle?

    As to check engine lights, I read them as don’t check engine. I could not care less unless the car is rattling, shaking or blowing black smoke. Typically emissions related nonsense. If you can’t be bothered letting me know the problem, don’t expect I will waste my time or money on an idiot light.

    • 0 avatar
      DenverMike

      Reading the code won’t necessarily tell you the problem, but it’s a place to start troubleshooting. Some obvious problems won’t throw a code, like stalling at speed (which actually helps emissions), so it may involve some guesswork, starting with the easiest, cheapest potential fixes, unless it’s the dealer (guessing) and you’re a cash customer.

  • avatar
    ttacgreg

    A few years back in the middle of Nevada, the check engine light went on in my 2000 Toyota Corolla. Wanting to be certain it was nothing serious I stopped in Winnemucca and found a car mechanic. He told me that they didn’t have the way to diagnose it, but stop at any parts store and they can run the diagnostic for free. I went to an O’Reilly’s. They told me it was an intake sensor and asked me if I wanted to clear the codes or not and I chose to clear the code. The light came on again intermittantly for the rest of my trip. When I got home I had the sensor replaced.

    A friend of mine chose to ignore his check engine light on his early 90’s Ranger. The probelem it signaled eventually plugged up his catalytic converter. Being in rural Colorado where there are no emissions inspections, he just had the catalytic converter removed. You seriously don’t want to be around his vehicle when it’s running, and I would hate to be behind him on the highway on a still air day. The exhaust is incredibly acrid and foul smelling.

  • avatar
    Tele Vision

    I mostly like the CEL. It’s a notice to plug the code reader in and check the health of the engine. Mine is on in the V due to evap system issues ( the charcoal filter ). I don’t like it because, other than the flashing mode for misfires, it can hide subsequent issues that have cropped up since it was first triggered by the original issue.

    tl;dr Buy a code reader.

  • avatar
    ToolGuy

    Changed the oil on my son’s car the other day (2006 Malibu 3.5L V6, it burns some oil and therefore needs oil added periodically). Was talking with my spouse and discussing the dry start-up (after the oil change) and the distinctive noise (which goes away of course) and the oil pressure light and the check engine light and the following questions came up:

    If you kept driving this vehicle and never added oil:
    A) When would the oil pressure light come on? (Remember it’s pressure not level) [How much damage is done at that point?]
    B) When would the check engine light come on? (Assuming no other issues with the vehicle.) [Would it be ‘too late’ at that point?]

    • 0 avatar
      Tele Vision

      @ToolGuy

      That’s a pretty old design and a low-compression engine. It’ll run on nearly no oil as long as there’s enough to generate pressure. During an oil change there is still a film of oil on all relevant parts, though, so it would be fine as long as there’s enough oil in the sump for the pickup tube to get to and pump up lifters. Oil pressure sensors are up top, where it matters, obviously. No damage would be done when the oil pressure light comes on – that’s a preventative warning. Imminent seizing might trigger a CEL but it didn’t on my wife’s 2013 Equinox: loss of power; shuddering; then blew all the oil out of the timing side. I had no idea that the 2.4L POS was an interference engine. It was a write-off, just a few months after the warranty ran out.

  • avatar
    Average Simp

    If we as Americans would just DEMAND we go back to carburetors on our pickup trucks we would be a whole lot better off. Give me a good ol American pickup truck, without all that plastic, a 4 barrel carb, no catalytic converters, ability to run leaded fuel, and while your at it roll the legal limit to drive back up to .10 or better yet .15

    Plus Jesus wants us to have 1.00 gas

    If God didn’t want us Americans to drink and drive he wouldn’t have given us pickup beds to throw our empty in.

    Gobbles

    • 0 avatar
      Lou_BC

      Carburetors, manual choke, mechanical ignition points, crank windows, manual door locks, the ability to start your vehicle in gear, gas tank behind the seat, 4 speed manual where the long shift throw lands you into a different time zone when changing gears, 2 and 3 speed automatics, three on the tree, manual heater controls….

  • avatar

    It is easy. It is Republicans to be blamed for that. They just want to keep people ignorant and/or misinformed. Okay in all seriousness how can you guys expect car companies to allow customers to be informed about what is going on with their car? Less information == less lawsuits. Imagine customer knows error code and tries to fix the car an gets hurt and then files lawsuit against automaker.

    • 0 avatar
      Average Simp

      If it were up to the Republicans vehicles would still have 4 barrel carburetors, no catalytic converters, no airbags, hell they wouldn’t even have padded dashboards or seatbelts.

      Because I’m a xxxxx supporter and it’s better to not wear a seatbelt that way your thrown clear of the wreck when you roll your pickup truck coming home from the bar.

      But the reason you crash is never due to intoxicated driving, cause hell ‘ol bub drives better that way. The crash was due to the slick roads, cause the Democrat treehugger didn’t use enough road salt.

      • 0 avatar
        28-Cars-Later

        Mercedes was offering fuel injection and ABS in the 70s, and air bags starting in 1980. The industry was moving in that direction regardless of political affiliation. Not to mention Nixon signed the NEPA in 1970, but well who needs facts right?

        https://media.daimler.com/marsMediaSite/en/instance/ko/40-years-ago-Mercedes-Benz-launched-the-drivers-airbag-and-seat-belt-tensioner-in-series-production.xhtml?oid=48190741

        Speaking of air bags, Ronnie years ago did an interesting piece on their history at my request:

        https://www.thetruthaboutcars.com/2014/06/automotive-archaeology-where-eaton-crash-tested-the-first-practical-airbags/

        • 0 avatar
          Average Simp

          Mercedes was moving that direction, many others were. Gm had airbags in 73. The fact is the dinosaur auto manufacturers were still making carbureted cars into the early 90s.

          The auto manufacturers fought airbags, remember the ridiculous seatbelt iterations they had as passive restraints before airbags came along?

          So get off it, your talking about companies like Mercedes, you could buy some American vehicles (trucks) without headrests into the 90s.

          The government mandated these things despite certain pressures from a certain political party and lobbyists hired by the big 3.

      • 0 avatar

        And what it has to do with my comment? Anything?

  • avatar
    Scoutdude

    Time to pull out the owner’s manual, any owner’s manual and do some reading on the subject. Many cars do tell you if it is a fuel cap problem and have a separate light just for that. Otherwise as you’ll find in every manual I’ve checked if the light is on drive on it is nothing that needs immediate attention. If it is flashing pull over as soon as possible as damage could occur if you continue to operate the vehicle in its current condition.

    The solid vs blinking is part of the OBD-II specification but something 99% of the people don’t know about since they aren’t automotive professionals and they never bothered to read that part of the owner’s manual.

    Doing anything beyond the CEL is not required and would not be useful to 99% of drivers, other than the check cap warning which was done purely to save the mfg and dealer money. They really don’t want to educate people that they need to put their cap back on and tighten it too. Of course some mfgs have gone to the capless filler for that reason, not primarily for customer convenience they tout it as.

    If people actually care about why it is on they can probably use google and find out just how cheap a bluetooth dongle and a basic app is and decide if having the ability to know why it is on is worth $20 or not.

    In fact if you really consider yourself a car person you really should have at least the most basic dongle and app.

    Personally I’ve got a couple of options. A couple of cheapo Bluetooth Amazon specials, a more expensive Bluetooth unit that also automatically does the Medium Speed CAN Bus and a hard wired version that also does both HS and MS CAN for use when changing settings, for example to account for a change in tire diameter, tire pressure due to a change in the tire’s load rating or adjusting the temp setting of the heated steering wheel.

  • avatar
    Jim52

    Hello Gang, I review daily but only on the rare occasion comment but hope to do more soon. The elephant in the room you have all left out — the dealer lobby has no interest in making this easy for the DIY or local grease monkey. Code readers for OBDII, even with advanced features, are under $100. That computing power is in every new or recent build car. Repair, real or imagined, is a cash cow.

  • avatar
    SCE to AUX

    One reason the CEL doesn’t tell you what’s wrong is that even the computer and its codes may not know.

    The only CEL I ever got in my 05 Scion xB was accompanied by a traction control light and skid control light. The CEL code was for something obscure. This occurred intermittently over a couple months.

    Applying some work experience I have, plus the data from the scanner, it turned out that the *trailing* O2 sensor was bad. A $75 part fixed everything.

  • avatar
    80Cadillac

    Counterpoint. The OBD-II diagnostic system is very useful, for anyone who cares to learn about it. If not, take it to a garage; you’re probably not interested in automobiles or have any talent for maintenance or repair.
    First of all, terminology. The industry abbreviation for this light is MIL, *not* CEL. That stands for Malfunction Indicator Light.
    The data port that is usually just below the lower edge of the driver’s side dashboard is the ALDL: Assembly Line Diagnostic Link. In OBD-I cars, the data port on some cars such as Ford or Toyota is in the engine compartment.
    As a teenager in the 80s, I would regularly check my parents’ cars for trouble codes. In a GM, you insert a bespoke key, or a paper clip or jumper wire, between the A and B terminals in the rectangular data port, then turn on the car’s power and count the flashes and pauses. 1-2, 1-2, 1-2 meant end of sequence, or all clear if no other numbers were indicated.
    In a Chrysler, you turned the car on and off rapidly 3 times, then on, and the “Power Loss” light would flash the numbers.
    Toyota, find the data plug under the hood and short terminals E1 to TE1, turn on the car, count the flashes.
    Similar for other manufacturers.
    For the 1996 transition to OBD-II, the rounded-corner trapezoidal ALDL became standardized globally, even if the software and some code definitions vary among manufacturers and continents. A code that is P0### is generic, and a code that is P1### is specific to the manufacturer.
    Caution: If you are shopping for a 1994 or 1995 GM product, check to see if it has the older rectangular ALDL, and avoid those. They are missing a contact in the B pin. GM began equipping some of its higher-end models with OBD-II beginning in 1994, and for this the EPA exempted them from providing a user/owner-readable interface on the other models.
    I worked in auto parts for a couple of years in the OBD-I era, and a couple of years in the early 00s, in the current OBD-II era. Early Ford codes were almost always due to carbon-clogged EGR valves. GMs usually threw codes for failing O2 sensors.
    OBD-I cars only had a few dozen possible codes, versus the thousands in the OBD-II system.
    An OBD-II trouble code gives you a good start to solving a problem, and it may not necessarily be as simple as swapping the sensor or component that is reporting unusual parameters. I remember a Grand Am with a MAP code (Manifold Absolute Pressure). So I ordered a MAP sensor for the kid. A couple of days later when he came to pick it up, I went to the car with him to show its location and how to change it. Turned out, the tube supplying the sensor had a hole worn in it. I went in and cut a few inches of tubing, gave it to him with no charge, and returned the part.
    Another time a man with a newer Buick LeSabre had an EVAP code. We checked the gas cap, erased the code, and I told him to bring the car back to me if the MIL returned. He was there the next day, and said the light was on, and the car had a MISFIRE, inconceivable on a 3800 only a couple of years old! The code indicated cylinder 2, front and center, but he didn’t know how to remove the engine cover for visual inspection. A twist of the oil neck and lifting the cover revealed a big ball of insulation where a mouse had nested, and had feasted on the fuel injector wire for cylinder 2. The man brushed all the debris out, twisted the bare ends of the wires back together, and was soon on his way. Never saw him again.
    A local banker brought me her Chrysler van, which was running rough on her trip home from a nearby town, with a *flashing* MIL. The 2 cylinders which reported misfire clearly corresponded with the numbers on the center coil of the coil pack. She was reluctant to purchase the $51 item, but I showed her how her husband could take off the plug wires and replace the whole coil pack with 4 bolts in a matter of minutes. Problem solved, and she likely saved several hundred dollars.
    I used to carry an expensive code reader for my own cars and friends’ cars, but it has probably been 10 or 12 years since I gave that away. I keep a $12 ELM-327 Bluetooth dongle (google it, they’re cheap and everywhere) plugged into the ALDL of my GMC, and I can access it any time with the $4.99 app Torque Pro, either for trouble codes or real-time data. I can easily take out the ELM-327 and pull codes from other cars, which I pretty constantly do for friends.
    It’s pretty difficult to know if there’s something simple like a thermostat stuck open on a pre-computerized car, but a trouble code indicating that engine temperature is lower than expected tells you exactly where to start.
    A friend recently changed the battery in her Lotus Elise, and because she didn’t know to back up the power, the various computer modules lost communication, resulting in an illuminated MIL that would not pass inspection. She searched Lotus forums, but only found owners shipping new computers all over the country. Others claimed that only a Lotus dealer, and not a Toyota dealer, could re-flash the computer. I did a pretty deep dive, and found an owner who had the correct code sequence of 2-digit numbers. I found an app that can write to the car through the ELM-327 (can’t remember name of the app off-hand). A few weeks later, she entered the sequence through her phone, and problem solved, no expense except a little time to find the right information.
    So I beg to differ about the usefulness of the MIL. I could relate hundreds of more instances of when the illumination of the warning light and the resulting code(s) have guided me straight to the solution. I do understand the point that the simple light does not give good information to the driver, and I would support a display message in plain language that summarizes the problem. In my opinion, the industry pulled a fast one in the popular “check engine” label of the MIL, because most of the trouble codes relate to ancillary systems, and not the actual reciprocating engine components. The warning light should simply say, or graphically communicate, “Malfunction Detected”.

  • avatar
    stuki

    I general, there is something fundamentally wrong with anything simultaneously complex enough to require diagnostics, and devoid of a simple and reliable way to hook up a general purpose terminal and get a shell prompt.

  • avatar
    AK

    For the author- buy a scan tool for $40. Problem solved

    That was easy and cheap.

  • avatar
    cdotson

    The OBD protocols were written by committees and enshrined in federal law. Viewed in that context all complaints are both validated and understood. Automakers have freedom to independently make the existing protocol more useful and more easily accessible above and beyond its current behavior so long as the system’s current behavior continues unchanged as legally mandated.

  • avatar
    Michael S6

    One of the dumbest causes for check engine light is forgetting to tighten the gas cap. I had this issue with my Infiniti G35 once and one of my friends recently had the same issue with his Toyota Camry. With all the onboard computers and displays, how complicated is it to flash a message saying “please try tightening your gas cap”.

    • 0 avatar
      ToolGuy

      That’s why the gas cap clicks (my understanding). Example owner’s manual verbiage: “Reinstall the cap by turning it clockwise until it clicks.”

      TTAC Survey: What percentage of licensed U.S. drivers realize their gas cap clicks when properly tightened? (My guess: 38%. I’ll be listening next time I’m at the gas station.)

      (A friend of the family, when her vehicle needs gasoline, she texts her husband. Pretty good system – for her. My family will not be adopting this system.)

      Get a Ford with Easy Fuel®:
      https://youtu.be/i2k1281Nb-I

      (Wait 5 seconds before removing the nozzle. Ford says this avoids drips.)

      • 0 avatar
        Lou_BC

        My truck has a self-sealing cap. This summer is was throwing a “check fuel fill inlet” message and then stopped on it’s own. The thing has started up again this week. A PIA that I’ve ignored. Truck runs fine.

    • 0 avatar
      Scoutdude

      It isn’t many mfgs have a check gas cap light or warning in the message center. That was done because dealers had way too many people with cars under warranty coming in for a MIL when it was just they didn’t tighten the gas cap until it clicked.

  • avatar
    IBx1

    The car is either new enough to be under warranty, or old enough to be well-documented.

    >$40 handheld scanner or $7 OBDII bluetooth/wifi dongle
    >Scan code, search google
    >If available, use service manual troubleshooting steps

    If you can’t be bothered to follow this simple a process, then you probably don’t care about cars and deserve to pay the dealership their share.

  • avatar
    Arthur Dailey

    It has been a couple of years but if I remember correctly having the ‘check engine light’ ‘on’ results in an automatic failure on the required emissions test in Ontario.

    • 0 avatar
      ToolGuy

      This was always my general understanding. Which is why I was shocked when my daughter’s Jeep passed an emissions inspection with the light solid on.

      (When we purchased her vehicle it had an issue which took some time to track down. Couldn’t get the vehicle registered without the emissions certificate. County Clerk office told me to go fail the test again to stay legal while the clock ran on repairs. Drove through the inspection lane and explained that I was about to fail – MIL solid on. Passed OBD-II-interface emissions ‘test’ and got a clean certificate from the worker who now regarded me as possibly of unsound mind. Mystifying.)

  • avatar
    gasser

    I have a Mercedes GLC 300 with under 10K miles. CEL came on three weeks ago. Since it is under warranty, back to the dealer it went. It was a failure of the evaporative canister, but you should see the list of what they had to check to hunt down the problem. Apparently there is also some sort of pump in that evaporations scavenging system. What I learned: I don’t want another ICE car. Even with a code reader, there is still too much to trouble shoot and my old technique of just serially switching out parts (still cheaper than the dealer) is too much $$$ these days.

  • avatar
    TheFirehawkGuy

    What you are referring to exists in aircraft today. See the Airbus ECAM for an example. If a system on the plane malfunctions there are 2 indicator lights, one for lower priority and one for higher priority, in amber and red respectively.

    Once triggered the aircraft will display text on the multifunction display regarding what the nature of the malfunction is and even what to do about it. It can even tell you what other systems are impacted by the fault.

    If Airbus can do this since the 80s then I’m sure auto manufacturers could do the same today. Especially since virtually all cars have built in displays. Heck, it doesn’t even have to be an up front in your face alert on the screen. Keep the CEL and when active a selectable notification dot can appear in the on screen menus. If a no clue driver gets a light and has no desire to dig deeper then nothing has changed. If someone with knowledge of mechanics wants to pursue more info then it is there for them.

  • avatar
    tankinbeans

    Sounds like it’s time to run an article about scan tool recommendations. Years ago I had a ScanGuage hooked up so I could monitor fuel mileage (yes, I’m that guy who has tracked mileage in every car he’s driven). The ScanGuage had the typical error bars so my calculated figures were usually different, but I figured if they were within a reasonable percentage of the expected mileage I was golden.

    Later that same ScanGuage, hooked to a different car – also primarily to monitor mileage, showed rising coolant temps. My car didn’t have a temp gauge, and only had a dummy light. I think the ScanGuage saved my backside in the new car I had at the time….Long story short somebody rear ended me, knocking a sensor loose, causing the thermostat not to function properly and I would have had no way of knowing.

    Fast forward to now and I have an inexpensive scanning tool, but I’m paranoid to use it. I was watching around on YouTube, YMMV, when Scotty Kilmer had one of his many click-bait video titles. “Using a certain type of scanner can fry your engine” or some other similar paraphrase. Of course the video doesn’t go into the scan tool that can cause issues, nor do I know the mechanism of how it could happen.

    Anyway, it seems like a recommended scan tool post might be in order.

  • avatar
    gasser

    +1 on Scanner tool evaluation.

  • avatar
    Daniel J

    Honestly, most of these cars have a USB input.

    These cars should have the ability to download diagnostic logs straight to the USB stick.

  • avatar
    ithappenedthatway

    I remember when the CEL was called an “idiot light”

    Times were simpler then.

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