Red Triangle, Code p0AA6

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by spacemanspiff, Feb 26, 2020.

  1. spacemanspiff

    spacemanspiff New Member

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    First time poster.

    2005 Prius 180K

    Current Status:
    Just replaced 12V battery. When I use the defroster, the red triangle comes on nearly immediately. The defroster and the heater functions still work until I turn off the car and then it will not turn on again. At that point, I can unplug the battery and then plug it in again a minute later to have the car reset and work again.

    Past year:
    In May and June, the AC would blow air but not cool. During the month of July 2019, the car was not used much. Just started once a week to keep it alive. In August, the car would not start until I added gas and oil. After this, when I used the AC would be loud and make a vibrating sound. It would also cause the red triangle to come on after a minute or so. In November, I started using the heater and defroster. Using the defroster would cause the red triangle to come on. I bought a cigarette lighter defroster. In January, the heater also started to cause the red traingle light.
    I brought it to a Toyota Dealer. They said the problem was the 12V battery and put it in a new one for $280.
    They read an error code of p0AA6 with no sub code. They said it is a "hybrid batt voltage sys isolation fault...which is a fancy way of saying the inverter is bad" Estimate of $6000 to replace the inverter.

    The car also has lots of wear and rust on the front and rear brakes, quoted for repairs about $600.

    How would you handle this situation? Any more understanding of these issues?
     
  2. dolj

    dolj Senior Member

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    You probably need to find a new mechanic, one who actually knows what he is talking about.

    P0AA6 is indeed an HV system ground fault, and I have not known it not to set sub-codes. There should be at least a 526 plus one other. Sometimes it needs a longer drive cycle to set the second sub-code.

    The P0AA6 can involve (usually one of) either the hybrid vehicle (HV) battery, transaxle, inverter or A/C'. You need the second sub-code to know which area is involved. Statistically, the HV battery is more common, but I still wouldn't just assume that without some supporting evidence.

    So before authorizing an inverter replacement, find someone who can do a proper diagnosis.
     
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  3. TMR-JWAP

    TMR-JWAP Senior Member

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    Everything in the OP leads to the AC compressor circuit, where it apparently has a grounding fault. Every time defrost is used, the AC system runs to dehumidify the air that's being sent to the defrost vents.

    I would probably disconnect the AC compressor HV power line at the inverter and see if the triangle issue goes away. Do some electrical checks on the compressor while it's disconnected. It may pop a DTC/CEL, but if the RTOD doesn't come on then I would think the problem is in the compressor motor/circuit.

    But, if you really need/want an inverter, I have three spares in the garage. I'd be happy to put one in your car for 1/6th the price that the dealer wants.
     
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  4. spacemanspiff

    spacemanspiff New Member

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    Interesting thought. My internet research had me thinking that it was the AC Compressor circuit as well. My research says in that case I would have to replace the whole AC system for about $1500. I told that to the repair shop but they did not agree or look into it and gave me the inverter information with no subcode.

    If it is the AC Compressor than would that fix the p0AA6 code or is there something else wrong with the hybrid battery?
     
  5. spacemanspiff

    spacemanspiff New Member

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    Thank you for the help. I will look for another technician in the Columbus, Ohio area.
     
  6. jerrymildred

    jerrymildred Senior Member

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    I'm pretty sure @TMR-JWAP is correct. The big red flashing arrow is that you first were getting the triangle when you used defrost. That turns on the air conditioner. I like his troubleshooting ideas. Disconnect the suspect to see what happens.
     
  7. jerrymildred

    jerrymildred Senior Member

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    I got a lightly used compressor for $100 and it cost $200 to have it put in by an AC shop that works on hybrids all the time.
     
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    The high voltage system of the car is totally isolated/insulated from the 12v system (and the car body). The P0AA6 code of which you speak is letting you know there is a significant reduction in quality of that insulation. The AC compressor is an electric motor that is powered from the HV system. If the cable going to the motor is damaged or the motor itself is failing, it could easily be the source of the P0AA6 code.
     
  9. jerrymildred

    jerrymildred Senior Member

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    Good point!, @TMR-JWAP. My previous answer assumes that it's found be be a HV leak in the compressor. It could also be in the wires to the compressor as noted above.
     
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