my prius’ check engine light

so my prius check engine light came on the other day. now, i knew from the internet that the most common cause of this is a loose gas cap.

so, i promptly unscrewed my gas cap and re-screwed it in. tight.

i started the car again. light still on. went to bed. started the car again this morning. the light was still on. drove to the dealer. light was still on.

i told the dealer the light came on, and i had checked the gas cap, and it was nice and tight.

a couple hours later they called me back. i was right. sort of. the thing is, at some point, the gas cap had been loose, and the car’s computer noticed it. according to the dealer, i have to drive the car for at least 20 minutes 2-4 times for the car to believe the gas cap really is fixed.

stupid computer!

$36 later, the sheet they gave me read:


at lunch, a coworker informed me autozone lets you borrow a tester that reads the codes from the car’s computer and allows you to reset the systems as needed. hmmmph.

in a way, i was punished for attentiveness. had i procrastinated and waited a few days to go to the dealer, the light would have magically fixed itself.

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  1. As you know, the check engine light indicates a problem with the engine’s emissions controls. Many of these problems may be intermittant. For this reason, the computer wants to make sure the problem is really solved before clearing the fault. (And lest you say it should know better in the case of the gas cap being loose, it may not know specifically that that is the problem–other problems, which could be intermittant, may look the same to the computer with whatever sensors it has available. Note that the mechanic checked other components of the evaporative emissions control system.)

    I would expect the owner’s manual to explain that you need to drive the car several times–does it?

  2. PS- I mentioned the Autozone thing in the comments on the This Is Broken article you linked to.

  3. I had a Ford Focus that would turn off everytime I rounded a sharp turn going faster than 25-30mphs. My dealer told me that it did that so that I wouldn’t run the turns too fast! They said there was nothing wrong with it and then I took it back about 1,000 miles later for a check engine light and they told me that the problem was that the car was trying to cut off when I rounded a turn! HUH? They tried to charge me for a problem that I brought to them months earlier. Crazy, crazy world.

  4. My VW Passat does the same “tighten the gas cap or else” thing. VW even warns you repeatedly in the manual that driving with the gas cap loose will damage the fuel level sender. At 19500 miles, the sensor that tells the computer if the gas cap is on tight broke. The dealer refused to believe me at first, but eventually they replaced the sensor and cancelled the code, all under warranty and in about 3 hours.

  5. 2005 Prius, “Check Engine” light. I read the above and went out and tightened my gas cap, took it off first, and then screwed it dow seven or eight clicks. Bingo! No more “Check Engine” light.

  6. You didn’t get ripped off at the dealer because they checked the system for you which should give you piece of mind that it is not something bigger than just the gas cap. I have a ford focus and my light is on and I WISH it was just the gas cap.
    And for angel: You should go back to the dealer and get refunded because the problem you have is under recall. The fuel pump was recalled on most foci for failing to send correct fuel pressure under large lateral loads just like yours was doing. (stalling around turns)search the net for focus recalls and take a print out with your vin# to the dealer and they should refund you. If you can find the letter that Ford sent you when they issued the recall that would be even better.

  7. Ok here’s a good one. Seems my Hyundia Sonada V6 is allergic to having it’s gas level hit the 1/2 full and 1/4 full mark. Heres how it goes… At 1/2 full stage the dang ” check engine lights ” comes on and goes out once the needle goes past the 1/2 full mark. Then just as it hits the 1/4 tank full mark here comes the check engine light once again. Never fails and no one; not even Hyundai dealers can seem to tell me why. Is this just one of one of a kind freaky car things or is really something other the replacing the gas cap which I’ve done like 3 times already to no avail ?

  8. so annoyed: sounds like a fuel pump problem to me I had the same type of problem on a dodge pickup..

  9. dam VW bug check engine light has been on since we bought it. Everytime we take it to emissions it fails. We now have our mechanic take it for us and he gets it to pass. Not sure what he does but there is absolutely nothing wrong with the car. I use to take it into the dealer but at $85.00 evertime we took it in was getting expensive and they could not find anything wrong with the darn thing…

  10. Wow! I just went to the Advance Auto shop, they told me exactly that… (Just “misplaced” my gas cap and lost it….emissions leak was the read ) ANYWAY, this light WILL reset if I keep driving on it?

  11. When you open the door, the dome light comes on immediately. When you shut the door does the dome light stay on for several 20 minute trips just to make sure? SOunds like a builtin dealer money maker to me.

  12. If your engine cuts off during a sharp turn then the problem is none other then the speedsensor. I had the same problem, even my speedometer used to shutdown and accelerator felt wierd and as soon as i do a sharp turn my engine stalled.

    Buy a speed sensor from the dealer (its very cheap) and try and fit it ur self as it only clips in clips out. or take it to a garage where they’ll charge u a tenner to clip it on.

  13. i have 1996 jeep cherokee sport-had a leak on exhaust header- car was spitting and sputering after it warmed up-tried jb weld kept breaking off -had it replaced car still sputters after two years-replaced fuel filter cap rotor coil numerous sensors -check lite always on-when it goes out the car shuts down -i have to wait 5 to 15 minutes-it starts lite comes back on-runs great and starts all over again about 20 minutes down the road-i put 70 miles a day on it–any ideas?

  14. i have a prius 2005 and the gas lid will not open when i pull the latch, how do i get the lid open to put gas into the car?? i don’t want to pry it open, also i have put wd40 on the lid when it was open, but still will not pop open?? help. thanks

  15. I have prius 2005 check engine light was on. I thighten the gas cap that fixed the problem; A guy from dealer told me when you do oil change if you put even a little more engine oil than you supposed to check the engine light will come on……………. my engine oil was fine.

  16. it happened to my prius yesterday morning.
    I went to dealer,service lady told me the cap and she did tighten it and light went off.
    they still went through testing and told me there is control close to water pump, there is a leak, maybe damage the control.
    total price $800.00 +.
    I reject repair.
    charged me $108.00 for the testing.
    this industry intentionally rob people blind.

  17. I have a 2007 prius, just had it serviced @ Toyota 2 weeks ago – general tune-up… the check engine light came on the day before I took it in. Told the technician this, and he replaced the gas cap ($26 part, $70 labor). Went to pick up car and check engine light was out…
    Last night the check engine light came on again. I stopped to get gas, and made sure that the gas cap clicked when I closed it. Check engine light still on…Don’t want to take the car back to Toyota to have them take a look at it if I don’t have to, any suggestions?

  18. one day while i am refueling the car , i left it on , suddenly at the same time engine check light warn up ,i think the issue is related to fueling system ,,did any one have this problem before.

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