Check engine light NOT coming on!! Emissions failed! Help!

Discussion in 'Gen 2 Prius Main Forum' started by Jcrew6311, Nov 13, 2021.

  1. Jcrew6311

    Jcrew6311 Junior Member

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    Went to get emissions testing done today, said they could test but I would daily because my check engine light wouldn't come on briefly at start up. I never noticed this before, but apparently yes, my check engine light doesn't come on at all. I'm the original owner and this has not been an issue before. 2008 Prius. Need this figured out soon and would prefer to not go somewhere for it.
     
  2. Jcrew6311

    Jcrew6311 Junior Member

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    Also, can't seem to find much of anything on this topic. All topics seem related to not being able to get check engine light off.
     
  3. ChapmanF

    ChapmanF Senior Member

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    In Gen 1 those were little light bulbs and could burn out, but I think they were already LEDs in Gen 2, so that is probably not the issue.

    If time is of the essence, I would immediately drop the twenty dollars on a TIS subscription (more info) for access to the repair manual and wiring diagram, and follow the troubleshooting steps for no check engine light.
     
  4. Jcrew6311

    Jcrew6311 Junior Member

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    Do you mind me asking...what on earth would make it not come on at all then? I Google search and can't find ANYTHING about it not coming on.
     
  5. ChapmanF

    ChapmanF Senior Member

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    If time is of the essence, I would completely skip the google searching and go straight to the repair manual, which has a diagnostic section for the exact situation.

    Naturally, you could guess the problem would have to be anywhere between the ECM, the wiring between it and the combination meter, to the meter itself. What you would want is how to pin it down among those possibilities. That's what the troubleshooting steps in the manual will help you do, along with the wiring diagram.
     
  6. Aegean

    Aegean Active Member

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    There a few things that need to be checked, first disconnect each connector one by one and turn on. If MIL comes on replace that part
    1. Throttle position sensor
    2. Water valve sensor
    3. Charcoal canister
    4. Vapor pressure sensor
    If no luck, check voltage to ECM, the harness and finally replace ECM.
     
  7. ChapmanF

    ChapmanF Senior Member

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    How do you expect that procedure to locate the cause of a MIL not coming on complaint? Are you thinking there is some way a defective throttle position sensor, etc., prevents the MIL from lighting up?
     
    #7 ChapmanF, Nov 13, 2021
    Last edited: Nov 13, 2021
  8. pasadena_commut

    pasadena_commut Active Member

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    While I agree in general that LEDs are more reliable than bulbs, they do still sometimes burn out. More often something driving them breaks, or somebody scrapes one off the board by accident with the edge of a tool.

    The OP should verify that all the other indicators light. Try rotating the dimming controller to see if the CEL is visible at maximum brightness (or better yet, visible when the car starts at night). Has the combination display been out to fix the capacitor problem? Whoever did that might have damaged the CEL bulb, or more likely, the wiring to it. I believe that the CEL can be turned on with Techstream, but it would be pretty amazing if that worked and it didn't light when the car starts. It looks to me like the CEL is not on the combination display, but I could be wrong about that.

    It is a PITA getting the instrument cluster out, but it seems unlikely that this can be fixed without doing so. See for instance:



    The odometer is on the combination display. You can pick up a complete instrument cluster at a junk yard or ebay for a couple of hundred, and then swap the combination display over to it to retain your odometer setting (and stay legal). Don't know how one would first test that the lights on that other unit work though.
     
  9. ChapmanF

    ChapmanF Senior Member

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    The picture in the owners' manual shows the MIL as one of the indicators off to the right of the speed display, which would put it on the meter circuit plate no. 2 (83247B in the parts drawing), for which there are two distinct part numbers depending on whether the car has smart entry. (Because no one understands the parts gods' sense of humor, the one for smart entry is a bunch cheaper.)

    [​IMG]

    Still, I would call it a mistake to go tearing in the dash or swapping parts unless and until the "MIL does not light" troubleshooting steps in the repair manual say to start doing that.
     
  10. Aegean

    Aegean Active Member

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    Yes this is correct. The procedure for MIL light not appearing is on the Prius service manual, engine control system chapter page ES-427 and ES-435.
     
    #10 Aegean, Nov 13, 2021
    Last edited: Nov 13, 2021
  11. mr_guy_mann

    mr_guy_mann Senior Member

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    The Check Engine Light (CEL) or Malfunction Indicator Light (MIL) on the Gen2 Prius is a LED in the Combo Meter assembly. It gets power from the 7.5 amp IGN fuse in the driver's side junction/fuse box and the ECM provides ground if it want to turn it on. You need the service manual for the wiring diagrams and connector pinouts and locations. Since the car runs, that indicates that the IGN fuse is intact. So you need to determine if: 12V from the IGN fuse is reaching the CM; the MIL circuit from the CM to the ECM is intact; the LED inside the CM can work; and if the ECM can switch that circuit to ground.
     
  12. CooCooCaChoo

    CooCooCaChoo Active Member

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    Turn the car on, but don't put it in READY mode. You should be able see all the lights on the dash come on. If the MIL light doesn't come on, its a burned out bulb.
     
    Another and privilege like this.
  13. Jcrew6311

    Jcrew6311 Junior Member

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    I greatly appreciate the ideas and thoughts on what this could be, but it seems like a bit of a rabbit hole, and to be honest I have more money than I have time right now with this issue. I need my car to get to work, we have a newborn plus 2 others, it feels well above my pay grade even though I've done a lot of my own work on our cars. How expensive of a repair could this end up being if I send it in to the dealer or a shop? I don't want to do that but it's seeming like the only way to get it done in a timely and guaranteed manner.
     
  14. Jcrew6311

    Jcrew6311 Junior Member

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    So, if it's a burned out bulb, is there any information online on how to access that bulb? Because I've found virtually nothing for it online.
     
  15. privilege

    privilege Active Member

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    hook up voltage to the cel and see if it illuminates.

    if it does, hook one of the other lights that are momentary to it, get your smog, carry on
     
  16. Another

    Another Active Member

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    Just curious
    Did you take the two seconds it would take to power on to see if bulb was burned out?
     
  17. Tombukt2

    Tombukt2 Active Member

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    In a state with emissions given all that's going on in the country right now you should be able to get a rider for a year. No problem just ask DMV.. it still clears tailpipe test?

    SM-A715F ?
     
  18. Jcrew6311

    Jcrew6311 Junior Member

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    yes I did that first thing, and nothing.
     
  19. Jcrew6311

    Jcrew6311 Junior Member

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    what's a rider for emissions?
     
  20. Tombukt2

    Tombukt2 Active Member

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    Usually in most states if you can't pass an inspection and your car's not polluting the planet IE can pass a sniff test up the tailpipe but say a light's not coming on or going off they'll give you a rider for a year like giving you a free inspection if you will and tell you after that you need to have it fixed so you have that whole year to fiddle fart around with it or not usually by then I have whatever straightened out and I just take it by the inspection place and they write it off and everything's good to go now I'm smart and I live in a place that doesn't even have inspection

    SM-A715F ?
     
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