Inverter or Transaxle failure and how to tell? (P0A7A P0A92)

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by BuckleSpring, Feb 19, 2023.

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  1. BuckleSpring

    BuckleSpring Member

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    Picked up a 2004 Gen 2 as a spare to use for parts, but got it home and it seems in unusually good shape so I think I'm going to try and save it. Is there any way to test the inverter rather than just replacing it?

    • Was originally throwing a P3009 HV Leak code, disassembled the pack, cleaned it up, tested modules, etc, and put it back together. Code went away.
    • Car will start and idle, 12v is charging, HV Batt is charging, throwing codes P0A92 (MG1 control?) and P0A7A (Generator Inverter Performance). Car will go into gear, reverses fine, will only go in drive up to ~15mph.
    I've basically narrowed it down to Inverter or MG1/Transaxle failure. Looking at posts on here, usually with MG1 failure it'll sound like a failing bearing or have some other weird noises, this one sounds normal.

    From looking around on the forum about codes P0A7A and P0A92, it would seem to indicate that MG1 has internally shorted or the insulation has failed or something. However, looking through the testing procedure as specified in the workshop manual and on other threads, the resistance between MG1 Terminals and between the terminals and ground is all within spec, other threads seem to indicate I should see a short to ground via one of these terminals if MG1 has truly failed.

    I'm currently waiting on a friend to get back from vacation to borrow his Megohmmeter, but from looking at other threads, the multimeter test should show something out of the ordinary if it's internally shorted. My miniVCI cable should arrive sometime next week as well so for the moment I'm relying on generic OBD2 codes.
     
    #1 BuckleSpring, Feb 19, 2023
  2. bisco

    bisco cookie crumbler

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    Congrats!

    techinfo.Toyota.com
     
    #2 bisco, Feb 19, 2023
  3. Tombukt2

    Tombukt2 Senior Member

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    Seems to me if my windings in MG1 or whatever you're testing seem to test good and I already have three inverters sitting around here anyway because I just do and I know they all work because they were all in a running cars when they were taken out and the lids have been kept on and they're out of the weather and all of that stuff I would have just swapped one out just to see it's only an hour and 20 minutes something pretty quick I couldn't wait for the general consensus of all of the whoevers I would have just swapped it out to see after I got the readings you did on my motor generator but no matter what I would do this is at your house. But it seems to me if the windings and whatnot and the things in MG1 and or two seem in the coordinates with the manual then it would be like you say the inverter or some control of these devices. So I'm guessing your battery computer and all that in your case looked good when you had it all apart?
     
    #3 Tombukt2, Feb 19, 2023
  4. ChapmanF

    ChapmanF Senior Member

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    It would help a lot to have a scan tool that can pull up the freeze frames for those codes and show you the INF codes.

    P0A7A especially has fourteen different INF codes that tell you very specific things about where the problem is. Depending on the code, it can be in the transaxle, wiring between transaxle and inverter, inverter, or wiring between inverter and HV control ECU.

    P0A92 also has a handful of different INF codes. Not quite the same gold mine of information, but also worth looking at.
     
    #4 ChapmanF, Feb 19, 2023
  5. BuckleSpring

    BuckleSpring Member

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    Unfortunately Mini VCI cable isn't here yet but should be here sometime next week so I can hook it up and read with Techstream

    Battery ECU looked good, no obvious signs of corrosion or anything on the connectors. I don't have a spare inverter on-hand and was hoping to avoid going and buying one before determining if that's what's really wrong. I'm borrowing a Megger to continue testing MG1 (and I'll check MG2 while I'm at it) to really determine what the problem is. 179600_upload_2019-12-21_12-38-10.png Screenshot_20230216-171254_2.png
     
    #5 BuckleSpring, Feb 19, 2023
  6. Tombukt2

    Tombukt2 Senior Member

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    Well that's cool it'll be interesting certainly to see what's taking a thrashing. I have a bunch of inverters and stuff like that around here just from taking these things apart It would bug me enough I would just change it just to see because I guess I can
     
    #6 Tombukt2, Feb 20, 2023
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    Did you do the motor winding resistance testing with a milliohm meter? Standard DVOM's don't have the precision needed for this test.

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, Feb 20, 2023
  8. BuckleSpring

    BuckleSpring Member

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    I did the initial test with a standard milliohm meter, other threads suggested if the problem was bad enough, something should've shown up. Just got back from testing MG1 with the Megaohm Meter and results aren't good:
    • Terminal U: 0.1
    • Terminal V: 0
    • Terminal W: 0
    So it looks like MG1 has failed unfortunately
     
    #8 BuckleSpring, Feb 20, 2023
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