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regenerative braking , e-assist acceleration much louder than usual

Discussion in 'Generation 1 Prius Discussion' started by carangil, Mar 2, 2015.

  1. carangil

    carangil Junior Member

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    155k miles, 2001 prius, original battery

    Today while driving, I noticed that regenerative braking seemed much louder than usual. When just taking my foot off the gas at around 30 or 40 mph, there was a noticeable harshness to the usual gentle hum. If I press on the brake lightly to engage more regen braking, it's louder.

    I took the car in the freeway for a short drive, and the on-ramp acceleration was louder than usual. I had full power, no check engine light, just a noise that tells me something is about to break.

    If I start to coast and I hear the loud hum, putting it in N makes it go away. Or at least makes it quier than the road noise on my junky city streets. I need to find a quiet freshly paved road, and a passenger with better hearing :)

    Braking from 30 mph to 0 while in N (no regen) sounds like it does in any other car.

    When I got home, I scanned for codes, and came up with a pending P0300, which is a misfire. Not sure if that's from today. See, a couple weeks ago the engine started with a rough idle and vibration that cleared up within a couple minutes of idling. (The roughness was similar to that occasional condition where when at a stop light the engine cuts out, but sort of chugs along rough for a couple seconds. I'm under the impression this is a common occurance among Prius owners. I've had this car for 3 years, and its only done it 2 or 3 times.)


    Any idea what could be wrong? Or should I just drive around until I get some horrible code?

    I also have a scanguage II, so if there's any xguages I should program to get extra data, let me know.

    Thanks!
     
  2. Britprius

    Britprius Senior Member

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    The noise is difficult to diagnose with any degree of accuracy. The likely suspects I'm afraid are not good.
    (1) Transmission bearing (one of the bearings in the transmission).
    (2) MG2 winding's short circuit.
    Both of these would realistically require replacement of the transmission.
    The fact that the noise goes away in neutral virtually rules out the wheel bearings.

    I am not conversant with the scanguage, but I do not think it will diagnose transmission problems "I could be wrong". In my opinion the Mini VCI is the best diagnosis tool. However until a DTC warning appears nothing is likely to show up. If your lucky maybe a fault pending code.

    I hope I am completely wrong with this diagnosis, and it turns out to be something easy.

    John (Britprius)
     
  3. valde3

    valde3 Senior Member

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    Scangauge should be able to read all the codes on Prius. But I think that MG2 needs to be pretty bad to cause fault code. And transaxle bearing doesn’t cause fault code at all. I don’t have any other guess about the problem. You should check the transaxle for leaking from where driveshafts go in. Normally bad bearing there will cause seals to leak.
     
  4. Aaron Vitolins

    Aaron Vitolins Senior Member

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    Have you ever changed the transaxle fluid?
     
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  5. Chuck Wagon

    Chuck Wagon New Member

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    This answer doesn't help the op, but I have noticed since purchasing our 2003 Gen1 this past Dec (95K miles YTD) Gen 2 & Gen 3 cars have considerably louder brake regen noises. I barely can hear this sound on our '03, it's almost as faint as say the turbo spooling sound on a forced induction ICE. I really can only hear it if I'm braking next to a large box truck, big rig or cinder block wall.

    I can hear Gen 2's braking from like 6-7 cars from behind. I'm new to these cars, and learning every day more about them, but I feel like the windings in the trans-axle may be giving up the ghost. I previously worked with high voltage electric motors in a previous trade, so the an audible high pitched sound wouldn't be uncommon with failing windings in an electric motor.
     
  6. carangil

    carangil Junior Member

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    I've never change the transaxle fluid. Toyota says don't bother. I should have probably known better.

    I put in the SG2 xguages for mg1 and mg2 temperature. At was 55F outside, and in the driveway MG1 crept up to 70F, and MG2 stayed at 55. Make sense, MG2 isn't moving when the car is still. After driving a bit (30 min drive to drop off my kid, and then to work) MG1 was at 110, and MG2 was at 180F. I noticed the peak was around 190 or so. So, based on everything I've read online so far, MG2 probably has half-burnt motor windings.

    I reset the odometer when I left home, and at the end of my drive I have 46 mpg, which is a little above average for my usual driving style. Maybe I was babying the car a little bit. But if I am wasting energy to heat, its not too much.

    Does anyone know what the ECU is looking for before it throws a code for this? MG2 temp is elevated, but everything still more or less works. Are there any preventative action that can be taken to stop the damage from progressing further, or am I just waiting for an imminent catastrophic failure?

    To make it worse, I still have the original battery, and at 155k, it probably doesn't have much life left in it. I won't know until that fails too. The two repairs together are probably way more than the car is worth.
     
  7. Britprius

    Britprius Senior Member

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    I would imagine the ECU is looking for over temperature, excessive current, and ground voltage leak. As I understand it a ground voltage leak on the gen1 does not put the car out of action.

    John (Britprius)
     
  8. Chuck Wagon

    Chuck Wagon New Member

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    Well you know how the saying goes..... Sell it while it's at it's best? But serious, those two repairs would easily exceed the value of the car. If you like the Gen 1 that much, you might be able to find a lower mileage one and drive another 3-4 years? I just bought a pretty nice one with 92K for $4500. God willing, I hope I could get at least 2-3 years of use out of this car without anything catastrophic. But I'm not going to lie (I didn't find this forum prior to purchase, or read who should and should buy a Gen1) So effectively this is one of the first cars that keep me from sleeping at night.

    That said I've previously owned some very maintenance scary to own German cars, that I have felt more confident in owning long term than my Gen 1. The only saving grace here, is that my Gen 1 is paid for, and is cheap to drive.
     
  9. carangil

    carangil Junior Member

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    I scheduled an appointment at Art's Automotive in Berkeley. They fixed my air conditioner a couple years ago when the refrigerant leaked out. I talked to them on the phone, and they said it sounds like the stator. I asked, and they do offer the stator-only swap if the rest of the motor and PSD are in good shape. Hopefully I can get out of it for about $2500 bucks or so, which is what I saw someone said the same thing cost at Luscious. Much better than Toyota's $5000 replace-everything procedure.

    After this is fixed, I might sell it while the battery is still good. Or not.. a battery swap I've heard can be in the low $2000's, so that's still cheaper that a down payment on something else. The way I see it if I can keep it going for less than what it costs to get something else, I might as well keep it going. I have no idea how long the battery will last; maybe I will be lucky and that'll be next year's expense. I imagine (and hope) once the battery and MG2 are in good shape, the rest is back to regular maintenance.
     
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  10. Aaron Vitolins

    Aaron Vitolins Senior Member

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    Keep us updated! For some reason i really like the Gen 1, its sorta rare and quirky/cute! :)


    oh, change the damn "tranny" fluid! after all its only 4 qts, and super easy to do!
     
  11. bwilson4web

    bwilson4web BMW i3 and Model 3

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    The temps suggest MGT2 stator. But the other symptoms suggest CVT only because no power in or out, little noise. Regardless, Art's has a solid reputation.

    Bob Wilson
     
  12. carangil

    carangil Junior Member

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    I've looked into a little bit, and if it is the MG2 stator (which I'm pretty sure it is. I found a youtube video of someone who had a fried mg2, and it was exactly the same noise), I know the low cost option is stator-only replacement. The source of stators is a new MG2, from which a stator is pulled out, and the rest of mg2 is scrapped. This is to save the labor of shimming in a new MG2, which I've found online is terrible work.

    Has anyone used Dorman parts? I knew they sold reconditioned prius batteries, but they also have stators on their site. I have no idea how 'used' this is, but would any one recommend / warn against this : Dorman Products - 587-990
     
  13. ChapmanF

    ChapmanF Senior Member

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    Dorman's a big, reputable firm, and they sell Prius batteries because they absorbed Re-Involt which was previously well known on this forum for pioneering techniques for battery remanufacturing. I'm really pleased to see they're offering stators - it's such a brilliant, obvious niche for someone to fill, when the alternative was to buy an MG2 and toss everything but the stator....

    -Chap
     
  14. ChapmanF

    ChapmanF Senior Member

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    Seems to be pretty new ... this flyer is dated February 2015!

    Says here they've altered the design, something about improved placement of temperature sensor. Would be interesting to know the details.

    -Chap
     
  15. carangil

    carangil Junior Member

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    Well, if I need a stator, I'll ask Art's if they've seen this yet. I'm willing to be the trial run of one of these if they're willing to try installing it. Maybe my car can be their next article. Anyway I've done all I can until my appointment on Wednesday.
     
  16. carangil

    carangil Junior Member

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    This is what Art's had to say:

    DIAGNOSIS PERFORMED / FINDINGS:
    Test drove car. Confirmed excessive wheel speed whine/growl when braking or coasting.
    The noise goes away when in neutral (MG2 & inverter aren't active in neutral). This eliminates wheel bearing or brake noise.
    Drove in reverse. Confirmed abnormal noise (but at a lower frequency due to slower speed).
    This leaves the MG2, differential carrier bearing, drive chain, and inverter. I don't think the noise sounds like inverter noise (this could be confirmed by swapping a known good inverter). All of the other components are in the transaxle.
    As far as the MG2 temperature goes. 200F would be way too high for the MG2 inverter temperature, but *may* be normal for the winding
    temperature. Toyota views this as proprietary information and does not publish a normal temperature range for the MG2. However, since there are no codes, 200F is most likely within normal range.

    RECOMMENDATION:
    Probably best to just replace the transaxle. If customer wants to be 100% sure the inverter is not at fault, recommend either a swap or a chassis
    ear check of inverter and transaxle case.​

    I talked with the mechanic over the phone for a while, and we talked about ways to rule out stator vs the rest of the transaxle. It may be the case that something else is going in the transaxle, and that it doesn't make any noise in neutral because the motor isn't really under load.

    He is also the instructor for a local community college hybrid tech class. So he invited me to the college that night, and my car was the class demonstration. They disconnected the inverter, and tested the motor stator directly. The results were inconclusive. They did three tests: 1) test with a milliohm meter. All three windings (U to V, W to V, U to W) read about the same: motor OK. 2) test with the 'all test pro' which measures more than just plain resistance. The highest winding reading was 10% higher than the lowest one, which suggests a bad stator. The third test, which is graphing the current rise time for a 12v load across the windings (a crude measure of inductane), puts all three windings within 5% or so of each other, which is acceptable.

    The mechanic thinks that while the stator may be starting to go bad, he doesn't think it would make such a loud noise, and thinks the noise may be something else in the transaxle. Usually the short in the motor eventually makes it way to ground and triggers a code. Leaving me with a few options.

    1. Ditch the car.

    2. Replace the transaxle. This will solve the problem, since everything it could be is being thrown out. But costs as much as a gen 1 that doesn't have this problem.

    3. Keep driving, until a) the short gets worse and a code confirms that stator is burnt, then replace stator or b) whatever else in the transmission is going out eventually breaks and the car dies.

    For now, I'm going with '3', since the car still has full power, and if it is the stator, the car should be drivable even with the code.

    My daily commute is 20 miles, and my office is near Art's, and we have a second car, so I'm sort of in a OK position to say drive until it dies.
     
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  17. bwilson4web

    bwilson4web BMW i3 and Model 3

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  18. ChapmanF

    ChapmanF Senior Member

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    Its standard alloy wheels with the contrasting painted pockets and machined/clearcoat faces have never been equalled for looks by any later-model Prius wheel Toyota has come up with ... sigh ....

    -Chap
     
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  19. carangil

    carangil Junior Member

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    As I've driven it around the last couple days, I now notice that at 25-30 mph, when in N you can hear the noise (but it is much much quieter than D) and at 60+ mph the noise is present in N (quieter than in D).

    The noise is the loudest when the electric motor is under load: either accelerating or decelerating. When at about 20-30, when I'm doing maximum regen braking (just enough brake to not engage the hydraulic brake), or I'm accelerating with electricity only, the hum seems to be made up of a pulses.

    Maybe I can grab a recording of the sound next time I'm driving. I wonder if the frequency of the pulses can be reconciled with the mg2 rpm given my driving speed. I would expect that if the noise was related to the chain or the differential bearing, the pulses would be at some multiple of mg2 rpm, depending on what gear ratios those parts turn relative to each other.
     
  20. ChapmanF

    ChapmanF Senior Member

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    The questions you're asking are exactly the ones I was looking at back in this thread a few years ago. I ended up lucky and my hum was a wheel bearing, but of course my first concern was the stator and so those were the gear-ratio and frequency calculations I was doing. Like you, I assumed a stator problem would produce a frequency simply related to MG2 rpm, so as soon as the calculations showed it wasn't, I just relaxed until I pinned down the wheel bearing.

    The end of that thread links to the later saga of my front wheel bearing, where the calculations were continued and revealed a possible way to tell rear from front bearings in the Gen 1. :)

    -Chap