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High Pitch Noise from Transaxle

Discussion in 'Gen 2 Prius Main Forum' started by Eclipse1701d, Sep 17, 2012.

  1. Eclipse1701d

    Eclipse1701d Prius Enthusiast

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    Hello all! Long time user, first post. I have learned a great deal from this forum and I hope someone can help...

    I have a 2007 Prius 3 Touring Edition. I purchased it new in Dec. 2006. I have had NO issues with my favorite car of all time, and currently have 90,600 miles. I have noticed a high pitch for a long time coming from the transaxle during acceleration. The pitch is only present when MG1 or MG2 is engaged. The pitch stops in stealth mode. My finance also has a 2007 Prius, and her's does not make the noise or whine when I drive her vehicle.

    I have changed the transaxle fliud at 65,000 miles, but I did not see the plug when it was changed so I don't know how much, if any, shavings were stuck to the magnetic bolt. If you are wondering, yes, the high pitched noise was present before the fluid change. Also, as I accelerate and increase speed, the noise pitch increases.

    Is my transaxle displaying a tell-tale sign of iminent failure? Or, does anyone else experience this same phenomenon?

    All TSB's have been performed and there are no codes or warning lights. Life time MPG is 49. My 12Volt is original, but I drive one to three hours a day and my voltage is good when I test it via the MFD diagnostic screen after sitting for 24 hours.
     
    #1 Eclipse1701d, Sep 17, 2012
  2. edthefox5

    edthefox5 Senior Member

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    Pitch stops in stealth mode? Hmmm. May not be trans. How about if you get up to speed and put it in neutral?

    Alot of posters report hum coming from front pass side when a winding short has occured but yours maybe bearing related in the diff which is why it has not thrown a check engine light.

    If it was me to rule out expensive trans I would dump the trans fluid asap and pay special attention to the magnet on the end of the dump bolt.
    First dump a pint or so after it has sat a while into a clean pan and look at it in the sunlight for pieces of metal. Like panning for gold. Should be very clean no metal at all.
    .
    If you see pieces of metal its done. Drive it till it howls. If fluid clean come back for more advice.
     
    #2 edthefox5, Sep 17, 2012
  3. Eclipse1701d

    Eclipse1701d Prius Enthusiast

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    Thank you for the reply. I suspected a bearing as well. I will try that this weekend and let everyone know the results.
     
    #3 Eclipse1701d, Sep 18, 2012
  4. jdenenberg

    jdenenberg EE Professor

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    You are probably hearing coil vibration due to the high current switching transients from the Inverter. Some Prii exhibit higher levels of this noise than others (mine does generate some). It is not a worrisome problem as it will not indicate a developing failure. My 2004 "whine" on acceleration (and the accompanying AM radio interference) was there when it was new and it is now at 239,000 miles and running strong.

    Transmission Howling is a different problem which is due to a motor winding insulation failure that causes a shorted coil. This usually requires trans replacement (a salvaged one will do so don't go for a $7000 new one).

    JeffD
     
    #4 jdenenberg, Sep 18, 2012
    PriusGuy32 likes this.
  5. Oldwolf

    Oldwolf Prius Enthusiast

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    My Prius C whines when accelerating, it is defiantly coming from the MG's or/and the inverter. On the other hand my Gen 2 is pretty much silent.
     
    #5 Oldwolf, Sep 18, 2012
  6. edthefox5

    edthefox5 Senior Member

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    I like the OP have an 07 and my Inverter is very quiet. You an hear it whine if its in Ready and the car is parked and your outside and ac on and the engine is off but never heard anyone complaining that it whines so loud you hear it in the cabin while driving.
     
    #6 edthefox5, Sep 18, 2012
  7. tdelker

    tdelker Junior Member

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    I have the same high pitch noise on coasting (no accelerator) and accelerating. I have understood from past posts this is normal for the electrical motors to do this. It's hard to hear because of the pitch, and I imagine some people can't hear it at all (read: older folks that don't have the range).
     
    #7 tdelker, Sep 20, 2012
  8. Eclipse1701d

    Eclipse1701d Prius Enthusiast

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    Okay everyone. I changed the transaxle fluid and there was a miniscule amount of metal shavings stuck to the magnetic bolt. I did not find any in the first quart that came out. Since this is only the second time a changed it, I believe they could've been in there from the first time it was changed. I say this because I have seen the inside of the transaxle and the inner walls are not smooth, but rather have squares with little ledges. I would imagine that during the first drain that they could've settled in one of those?

    The pitch I hear is only present during acceleration and increases with speed, then decreases while slowing down. It also stops in stealth mode. It's not so loud that you hear it all the time, just with the radio off and only when being attentive and listening for it. So, at this point, I am comfortable with the inverter being the source.

    I might add to the discussion that I am cursed with super-human hearing. I hear noises and pitches that most people cannot. My piano has lock-tight on the screws and felt added to the panels because I could hear the vibration when I played and it drove me crazy! :)
     
    #8 Eclipse1701d, Sep 21, 2012
  9. edthefox5

    edthefox5 Senior Member

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    #9 edthefox5, Sep 21, 2012
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