Hooniverse Asks: What's the Stupidest Reason You've Gotten a Check Engine Light?

Is there anything quite as frustrating as an inscrutable Check Engine Light that taunts you cryptically from the instrument panel? What could it be, a failed sensor impending a certain catastrophic mechanical end? Or maybe you forgot to put the gas cap on with the requisite three clicks once tight.
That a CEL can tell so much while actually saying so little singularly makes it the most frustrating piece of automotive technology in existence. And car makers want it to stay that way. You might note that in the section of your car’s owner’s manual describing the CEL the most common advice given is to get the car checked out by an authorized service provider at your earliest opportunity. Should the CEL be flashing the advice is to stop immediately and have the vehicle towed there posthaste, along with your wallet. Never mind the tsunami that’s rapidly filling your rear-view mirror.
As the possessor of more than one old but not that old car, I have seen my share of CELs. One of the best purchases I ever made was of an OBDII reader which is needed to decipher the enigmatic and secretive light. I’ve discovered problems from the mundane to the extreme, and have felt the frustration that they’ve all been consigned to one single unchanging lamp. I’m pretty sure most of you feel the same way that I do, and I’m wondering in that case, what’s the stupidest reason you’ve ever gotten a CEL, and did its discovery involve a service department?  
Image: KefferMazda

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31 responses to “Hooniverse Asks: What's the Stupidest Reason You've Gotten a Check Engine Light?”

  1. P161911 Avatar

    Stupidest, “engine fan speed” on the Trailblazer. It means the fan clutch is going bad and it fails in the on position, so it just hurts the MPG a little bit, also keeps it from passing emissions. At 168k miles, I have now replaced the fan clutch 3 times.
    Most frustrating: “Lost communication with ECU”, completely intermittently, cause engine stall about once every 5k miles or so, restart is somewhere between instant and 5 minutes.

    1. Atomic Toast Avatar
      Atomic Toast

      Seems unusual for the fan clutch to fail three times on one vehicle,poor design or cheap manufacture?

      1. P161911 Avatar

        Two of them might have been related to water pump failures, not sure which one came first. Replacements have all been aftermarket parts.

  2. Sjalabais Avatar

    I test drove a Legacy wagon once with the CEL on. It was priced…competitively. The sleezy seller was the kind of guy that obtains cars cheaply, and resells them just a little bit more expensive. He told me the light was on because it was raining. Your very own weather observation, just in case something’s unclear about that. It was easy to see that the engine slurped oil, the coolant was dirty and below “L” – “just changed something on the engine, that’s why”. He wouldn’t even meet me to take the car back, and instructed me to park it in an industrial area, and hide the key on one wheel.

  3. Kiefmo Avatar

    Before manufacturers started making a dedicated warning for it, a loose fuel cap could cause a CEL.

    1. P161911 Avatar

      It still does on most cars. When did they start making a dedicated light?

      1. Wayne Moyer Avatar
        Wayne Moyer

        Yeah I got it for my 2012 Dodge Grand Caravan.

      2. Kiefmo Avatar

        I am not sure, but I swear I’ve seen a “check gas cap” light on a car. Or maybe it’s on cars with big screens that display more than idiot lights?

        1. Papa Van Twee Avatar
          Papa Van Twee

          When I test drove a Cobalt, it came up on the radio screen. Maybe it was a Malibu Maxx? One of those with the stereo with the big button/volume dial dead center.

    2. Lokki Avatar

      A few years ago the gas cap on my 98 328i (69,341 miles as of this morning) simply got old and developed a leak at the seal, causing a check engine light and much consternation. Buying a new gas cap fixed things, but not before a lot of annoyance, inconvenience, and expense.

      1. Sjalabais Avatar

        Is it possible to read out the error message with OBD tools?

        1. P161911 Avatar

          It just shows as “Leak in evaporative emissions system” or some such. 98% of the time this is a loose or bad gas cap. UNLESS, you happen to own a Trailblazer which had a bad batch of plastic gas tanks that developed a very tiny crack in the fuel filler neck area. GM eventually recalled most, but not all of them.

      2. Rover 1 Avatar
        Rover 1

        … and expense and a huge amount of swearing. (In my case) It’s the first thing I check now.

        1. Lokki Avatar

          The problem was that because the cap seal was bad, but not visibly so, removing and reseating the gas cap didn’t fix the problem like it normally would.

          1. Rover 1 Avatar
            Rover 1

            Yes, check for the inrush of air sound.

  4. 0A5599 Avatar

    Some light corrosion or something changed the resistance reading of the chip in the key. Security light came on and the ignition inhibitor prevented the car from starting until the required wait time elapsed–10 minutes or so.

    1. Jeff M Avatar
      Jeff M

      That’s not the “CEL”.

      1. cap'n fast Avatar
        cap’n fast

        yes but, it’s even better than a CEL.

        1. Jeff M Avatar
          Jeff M

          No, no it’s not, but thanks for playin’

  5. Alff Avatar

    My 15 year old pickup has a perpetual CEL. The original fuse box (“Power Distribution Center” oooh) has a design that renders it susceptible to failure by corrosion. There’s a short supply of replacements. When you can get one they run north of $600. I purchased one for less than half of that from a dealership that was shutting its doors. I don’t know what vehicle it came from but it is slightly than the original – the pinouts for the AC Fan are different. I’ve never bothered to correct this, although it would be a pretty easy fix. The difference triggers the CEL.

  6. mdharrell Avatar

    Sorry*, I’ve never owned a vehicle new enough to have one.
    *Not actually an apology or indication of regret.

    1. Vairship Avatar

      “L’OBD, c’est moi!”

  7. ptschett Avatar

    There was a time that the conventional “wisdom” was to use conventional spark plugs instead of the specified double platinums in non-PI 4.6L Ford engines like my ’96 Thunderbird’s. In return for the 0.03 HP gained, it would develop a misfire about annually or every 12-15,000 miles. Then I installed factory spec plugs at ~100,000 miles in 2004 and was trouble free in that regard for the next 9 years.

    1. Alan Cesar Avatar
      Alan Cesar

      That misfire happened because conventional plugs wear out every 12,000 miles or so. That was a big reason cars used to need an annual tune-up.

  8. Hillman_Hunter Avatar

    Because I bought a VW

  9. tonyola Avatar

    High humidity (a frequent condition here in Miami) and a cold engine sometimes caused the CEL to come on in my 1990 Civic. The mechanic said it had something to do with an oxygen sensor and to pay it no mind. Never had any notable problems.

  10. smokyburnout Avatar

    Check Engine Light on and bad catalytic converter code but it’s actually just an ECU miscalibration

  11. Andrew_theS2kBore Avatar

    Installed a throttle body gasket upside down. The dustbuster-from-hell noise gave it away as soon as I opened the hood.
    *My stupidity, not the car’s.

  12. jeepjeff Avatar

    Alright. I’m going to cop to this one. I’ve got a Wrangler, so the gas cap doesn’t have a lock or a tether, so I normally set it on the rear bumper while I’m filling up. One time, I forgot it there and a little ways down the road, it threw the evap code for a broken cap. Too late to go find the cap anywhere… I felt pretty stupid buying the replacement cap at the parts store.

  13. cap'n fast Avatar
    cap’n fast

    went out to start my ranger in the chilled january dawn, and had the CEL on as soon as the key turned on. found squirrel nesting in the engine bay above the ignition chewing the wiring insulation. shorted wires together. fried the harness. good indication something is amiss when starting the truck is smelly smoke curling up from the TFI harness and a pissed off chittering from under the hood. relatives wonder why i do not like tree rats.