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can mg2 begin to fail without a trouble code?

Discussion in 'Generation 1 Prius Discussion' started by pmc, Feb 13, 2023.

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  1. pmc

    pmc Junior Member

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    Hi all,

    Mileage for my '02 has recently dropped from mid 40s to mid 30s. I know there are several possible causes and I have troubleshooting homework to do. But I have a specific concern before I go drive a few hundred miles of expressway.

    Can mg2 begin to fail without setting any trouble code?

    Sometimes I hear a mild tonal rumble. I haven't been able to quantify the frequency/speed relationship well enough to rule out the ~60Hz/60mph freq reported for mg2 badness. Or positively identify a different cause. I don't have ready access to a scanner that will report mg2 temperature. If mg2 is just starting to die, I'd rather not flog it to death mid-journey.

    A dealership service guy assures me that mg2 can't be starting anything bad without tripping a trouble code. Should I believe him?
     
    #1 pmc, Feb 13, 2023
  2. ChapmanF

    ChapmanF Senior Member

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    Any chance you could just report what the tone is, at a few different choices of speed? If you're a musician or have a musician friend you could just match the pitch with a tuner or a tuned instrument (or your ear if you have absolute pitch). Then more than one of us could be thinking about it in parallel.

    I remember working on that question myself in this thread and later again in this one.

    For me, it didn't turn out to be an MG either time. Both times were wheel bearings. At least I learned a bit about characteristic pitches for Gen 1 rear and front wheel bearings. At least for the front one, I was able to kind of justify the observed pitch from the geometry of the bearing. I never examined the rear bearing that closely, but its (different) relation of pitch to road speed probably has a similar explanation.

    I'm not sure at what point a trouble code would be set. You might look into some stuff written by Art's Automotive or by Luscious Garage, where they did some MG replacements, and see if they say there was always a code early on.

    In my case, that first time, just figuring out that the pitch I was hearing did not match what I'd expect from MG2 made me feel a lot better.
     
    #2 ChapmanF, Feb 13, 2023
  3. pmc

    pmc Junior Member

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    I haven't succeeded at this yet. I don't have the ear to do it without reference to a pitch standard. I've tried while riding with my wife driving but haven't heard the mystery noise on those occasions. Kinda frustrating.

    Yes - thank you for writing that up!

    Yes - that would help for sure! It's also just what I I haven't been able to do yet, but only get close enough to say I can't rule it out. :-/ I'll continue trying to get noise & pitch reference together. Or a recording or whatever.

    This question is an attempt to get there by another way.
     
    #3 pmc, Feb 13, 2023
  4. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I look at it like this:

    The computer is constantly studying all kinds of metrics from the power electronics, the MG windings, the wheel speed sensors and system voltage. It has a lot of cross-checks built in.

    It is also reading exactly nothing from the wheel bearings; no instrumentation installed.

    I'd bet on the bearings being worn out.
     
    #4 Leadfoot J. McCoalroller, Feb 13, 2023
  5. pmc

    pmc Junior Member

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    Yes. That has been my play for the last couple of weeks.

    I'm about to raise both the stakes of the bet and load on the part. Or adjust plans while I still can. Or (preferred) shift the odds from "bet" to "forget" go flog parts that degrade more gracefully.

    edit: weird lost draft but not really
     
    #5 pmc, Feb 13, 2023
  6. Tombukt2

    Tombukt2 Senior Member

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    If you haven't replaced the wheel bearings on this particular year model vehicle I would certainly think that would be a place to be looking first.
     
    #6 Tombukt2, Feb 14, 2023
  7. pmc

    pmc Junior Member

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    I agree.

    Also: before I get to the bearings I expect to drive enough distance at speed up hills to significantly aggravate a marginal stator at a time when killing my car will affect other people. Or do something different to avoid that avoidable hazard if I can't rule it out.
     
    #7 pmc, Feb 14, 2023
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