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Check engine light on, then off

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by WilliamRDickson, Sep 20, 2022.

  1. WilliamRDickson

    WilliamRDickson New Member

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    Left my 2005 at the body shop for 10 days while on vacation. Picked it up Monday, check engine light was on. Drove it maybe 20 miles, still on. Filled tank, mileage average reset itself, which I’ve never seen happen without me manually resetting, but I haven’t had the car that long. Made appointment at auto shop to check it out.

    Today, drove it to grocery store. Light still on. Came out to drive home…light’s off. Stayed off all the way home. Still off.

    This sound like anything in particular? I plan to give it a couple days and see if it comes back on, but if it doesn’t, should I still have it checked out? Was maybe the battery just run down from sitting, and it needed to recharge some?


    iPhone ?
     
    #1 WilliamRDickson, Sep 20, 2022
  2. JC91006

    JC91006 Senior Member

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    If this was a guessing game, it probably is an intermittent failing catalytic converter
     
    #2 JC91006, Sep 21, 2022
  3. Tombukt2

    Tombukt2 Senior Member

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    Don't do anything till you have a solid code then read the code from the OBD2 port with the proper or some sort of scanner and see what you got like the other guy said I bet it's the cat low threshold That's the most common seemingly thing that starts all this 200,000 miles plus almost guaranteed That's the only time I check engine light comes on for the most part is for that PO420 cat below threshold All the other codes I get don't seem to bother the light so much the check engine light they light up the triangle or the car on the MFD turns red
     
    #3 Tombukt2, Sep 21, 2022
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    The light came on because something was wrong enough to fall outside of what the ECM is programmed to allow- so it set a code. The fault is intermittent, the ECM saw the problem wasn't there several times so it turned off the light.

    Whether it will happen again is unknown. You can wait until it (might) happen again- or not. It's your car and your money. If you don't get codes checked very soon, then the ECM will erase whatever code it had.

    Posted via the PriusChat mobile app.
     
    #4 mr_guy_mann, Sep 21, 2022
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  5. WilliamRDickson

    WilliamRDickson New Member

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    So it sounds like I should probably cancel my appointment (since the code will likely have cleared by then anyway), order myself a scanner (like so? https://amzn.to/3tN3cB5) and check it myself if the light comes back on, and then proceed from there.

    Thank you all!


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    #5 WilliamRDickson, Sep 21, 2022
  6. pasadena_commut

    pasadena_commut Senior Member

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    Obviously the best course is to plug in a OBD2 reader the next time you get a code.

    Probably this isn't it, but maybe the gas cap was loose at the body shop? That will trigger a CEL. When you filled it up you screwed it in tightly and so the CEL reset some time later. The reason that probably isn't it is that that sort of CEL usually resets immediately, the next time the car starts. It wouldn't hurt to take a close look at the gas cap though. If it is old and any of the rubber is cracked you may see mysterious CELs come and go as it seals and unseals.
     
    #6 pasadena_commut, Sep 21, 2022
  7. ChapmanF

    ChapmanF Senior Member

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    Even if the light is now off, connecting a scan tool that is able to display 'permanent' and 'history' codes may well prove useful.
     
    #7 ChapmanF, Sep 21, 2022
  8. WilliamRDickson

    WilliamRDickson New Member

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    Actually…there *was* something weird when I filled the tank. There was a loose strip of white foam wrapped around the inside of the gas cap cover, like a gasket, absolutely soaked with soapy water. I couldn’t tell if it was supposed to be there, and the body shop had dislodged it while washing the car, or if it was just something they shoved in there while painting for some reason. My mother’s 2004 doesn’t have one, but it’s been through a lot, so I didn’t take that as definitive.

    It interfered with properly opening the cover. It’s possible they also left the cap loose if they were fiddling around with it.


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    #8 WilliamRDickson, Sep 21, 2022
  9. pasadena_commut

    pasadena_commut Senior Member

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    Just to be clear, that foam was under the little door, or it was under the gas cap itself? Either way, if it was wet in and around the cap some water might have entered the tank when it was opened, and that could have made the car run rough enough to throw a CEL.
     
    #9 pasadena_commut, Sep 22, 2022
  10. WilliamRDickson

    WilliamRDickson New Member

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    It was under the door. It was actually lining the inside edge of the door, and one edge of the foam was clearly adhesive but had come loose. It *almost* looked like it was supposed to be there (it conformed very neatly to the edges of the door), but based on your reaction I’m going to assume it’s not.

    This body shop forgot half the work I asked them to do, so I shouldn’t be surprised if they left soggy foam where they shouldn’t have.


    iPhone ?
     
    #10 WilliamRDickson, Sep 22, 2022
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