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Slight shudder and then triangle- P0A7a code- What is it?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by aleyoop, Dec 2, 2022.

  1. aleyoop

    aleyoop Junior Member

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    Hey Guys,

    I was driving my 2008 w/ 180k and at low speed acceleration (10 mph) i felt a slight shudder and the triangle of death came on. Car drove just fine and when i stopped and checked- it was the P0A7A code. Cleared the code and drove the car home. No other codes shown.

    This is the second time that the same things happened. Low speed acceleration--slight shudder and triangle. The first time it happened, the car drove very slow and wouldn't accelerate beyond that. I cleared the codes and for the last 1500 miles, its driven fine. This is now the second time w/ the same issue.

    Inverter pump and coolant was changed and i confirmed that it is working fine (i can hear/feel the noise and coolant is moving in the reservoir).

    Any ideas on what this could be?
     
  2. bisco

    bisco cookie crumbler

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    sounds like an intermittent problem, maybe due to poor connection/corrosion/rodents?
     
  3. TMR-JWAP

    TMR-JWAP Senior Member

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    There are 14(?) subcodes associated with a P0A7A to help narrow down the issue. Did you happen to get that before clearing it?
     
  4. aleyoop

    aleyoop Junior Member

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    I didn't see any subcodes. Is there any special way you're supposed to access those? I have a run of the mill obd
     
  5. SFO

    SFO Senior Member

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    Many like to use a 'mini-vci' cable (or better), and the dealer diagnostic software 'techstream' on a winblows device (can also emulate).
     
    aleyoop likes this.
  6. aleyoop

    aleyoop Junior Member

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    Hey Guys,
    So i got the triangle again and this time i ran techstream to identify it.

    It's the P0A7A-325 subcode. Any idea what this could be?

    The issue is always the same...slight shudder at low speed acceleration and then i get the triangle...car still works just fine. Mileage has been 4-5 mpgs lower than before as well...

    thank you so much!
     
  7. SFO

    SFO Senior Member

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  8. aleyoop

    aleyoop Junior Member

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    Thank you^

    Much appreciated. Looks like it could be any number of these problems!
     
  9. bisco

    bisco cookie crumbler

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    yeah, that's a tough one. check the a/c connector, that seems to get a lot of corrosion
     
  10. ArrowheadVenom

    ArrowheadVenom Junior Member

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    I have this EXACT problem on my 2005, exact same code and subcode, exact same behavior. I have already replaced the inverter/converter twice, if that helps. I have not made it all the way through that work up because it's pretty confusing and the final steps are either "replace inverter" or "replace transaxle" or "replace HV control ECU", even though the problem could theoretically be wire connections between these components.
     
  11. ChapmanF

    ChapmanF Senior Member

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    The connection possibilities are checked for in the first few steps of the workup, the ones whose "NG" branches are "connect securely" or "tighten them to specified torque". Once you're past those steps, the ones that are left are the ones that tend to implicate the ECU, inverter, or transaxle.

    Step 6, of course, calls for both a milliohmmeter and a megohmmeter—both of which are rather specialized instruments and take a bit of training. The ohms range on your day-to-day multimeter won't cut it. Do you have those instruments, or access to someone who has them already and has been trained in their use?

    The training for those instruments includes safety considerations. A megger uses a high voltage to test with, 'nuff said. A milliohmmeter uses a friendly-looking low voltage, but when you use it on something with many turns of wire, like Prius MG windings, you need to know what you're doing at the end of your test, because the energy stored in that magnetic field will be coming back atcha.
     
  12. ArrowheadVenom

    ArrowheadVenom Junior Member

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    Thanks, although I have replaced the inverter twice (which involves reconnecting and re-torqueing all the inverter connections), and I have checked the HV ECU connector in the glove box area.
    So for me the only remaining solutions in the work-up, regardless of diagnostics, are to replace the ECU or transaxle.
    I don't have access or training for milliohm or megaohm equipment, but through process of elimination I may as well replace that ECU if I can find a cheap one (junkyard). Then if the problem doesn't go away, it must be the transaxle, right?
    I mean I'll probably triple-check all inverter connections just for good measure since it's a free and easy thing to do...

    My suspicion is that my transaxle has some kind of damage to a coil or a tiny flake of metal floating around, such that usually it's fine, but when stopping, it may settle in such a way that it causes an internal short for a split second, then it's fine again.
     
  13. mr_guy_mann

    mr_guy_mann Senior Member

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    Then try replacing the transmission fluid. If you see a bunch of sparkles in the old fluid- then there you go.

    Posted via the PriusChat mobile app.
     
  14. ArrowheadVenom

    ArrowheadVenom Junior Member

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    Forgot to mention I did that as well a while back. Fully drained and refilled using a hand pump, till it reached the level of the fill hole. No change.

    But it could be something that's not gonna drain out in the fluid so easily.
     
  15. ArrowheadVenom

    ArrowheadVenom Junior Member

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    Is that the smaller orange high voltage connector at the front left of the inverter?

    And how would it be related to this problem exactly?
     
  16. bisco

    bisco cookie crumbler

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    no, it's the one at the a/c compressor. the codes only point to a high voltage leak, could be anywhere
     
  17. ArrowheadVenom

    ArrowheadVenom Junior Member

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    Is there any way this could be related to an isolation fault in my hybrid battery? My hybrid battery has always been missing the thin little isolation strip of metal that sits across the main positive and negative high voltage wires right as they enter the battery case. (I got the car used and the hybrid battery had clearly been refurbished and they left out that part. I got new battery cells later).

    My research has shown that an isolation fault would throw a specific code though. I would replace this little piece of metal, but I can't figure out where to buy one.
     
  18. ArrowheadVenom

    ArrowheadVenom Junior Member

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    Another thought occurred to me. A couple months ago I had to replace the inverter coolant pump as it had failed completely. It seemed to work back when I first noticed this problem, so I just replaced the inverter then. And the problem was gone for a while but then came back. Replaced the inverter a second time (they are not that expensive used from junk yards). Same deal, it was gone for a little while but then came back. Even when it came back it's been very intermittent.

    What if I had a failing pump that has caused 3 inverters to overheat and get damaged? Should I replace it for a third time? This time with a working coolant pump such that it won't overheat again
     
  19. ChapmanF

    ChapmanF Senior Member

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    There are a lot of threads here about isolation faults, and the code for that, which is P0AA6. With this thread being about a different code, I would want to avoid mixing up those issues.
     
  20. ArrowheadVenom

    ArrowheadVenom Junior Member

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    In case anyone else is reading this, I think my problem is solved. My hybrid battery was going bad, and when I swapped it for a Nexcell lithium kit, the p0a7a has never happened since. It's been over 3 months and several thousand miles.
    So, as mysterious as it is, I think this is not an inverter problem at all; it's a hybrid battery problem, which freaks out the inverter.