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Diagnosing Check Engine Light

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by gsbeliever, Mar 19, 2016.

  1. gsbeliever

    gsbeliever Junior Member

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    The check engine light came on in my 2009 Prius so off to Autozone where the OBDII said "Evaporative Emission System Leak Detected (very small leak). They thought it was probably my gas cap, so they reset the codes, I bought a new cap, and everything was fine for 4 days. Now the check engine light has reappeared and I have to get my car inspected next week.
    Any good places to start checking? Thanks in advance,
    Scott
     
    #1 gsbeliever, Mar 19, 2016
  2. JC91006

    JC91006 Senior Member

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    Can you post the code(s) that were read? Sounds like the autozone guy wanted to sell you a gas cap
     
    #2 JC91006, Mar 19, 2016
  3. ChapmanF

    ChapmanF Senior Member

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    The evaporative emissions system (on any car) can be one of the most, hm, interesting systems to diagnose. There are a bunch of places a small leak could be (the gas cap was a reasonable guess, it's common and easy to try), the test pressure tolerances are really low, and any kind of testing with air (or any mix that includes oxygen) is a really bad idea. (Shops can use nitrogen, with a tested and trusted very-low-pressure regulator.)

    If you google evaporative emission diagnosis you can get a lot of good info.

    The details on your specific evap system will be in your manual at techinfo.toyota.com. Another PriusChat member who recently logged in there made it sound like a lot of the "University of Toyota" training downloads are there too. The ones on the evap system are very explanatory and helpful.

    -Chap
     
    #3 ChapmanF, Mar 19, 2016
  4. gsbeliever

    gsbeliever Junior Member

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    Chap,
    Thanks for the useful info, I'll do some research at that site. I did borrow a friend's OBD and it read exactly the same as Autozone's. After googling the problem, sounds like there's lots of possibilities, from a leaky fuel pump gasket to all kinds of issues. Car runs great (130k miles) but any check engine light is an automatic fail on my annual DMV mandated inspection.
    Thanks
     
    #4 gsbeliever, Mar 20, 2016
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