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"Check hybrid system" failure & P0A0F code

Discussion in 'Gen 3 Prius Technical Discussion' started by Jim Caldwell, Aug 31, 2019.

  1. Jim Caldwell

    Jim Caldwell Member

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    Have a 2010 prius 3 with 140k miles. Its showing the check hybrid system message. Have tried to get car started and failure cleared by charging and jumping the 12v battery. With it jumped, still wont run. I have tried disconnecting 12v batt for 10 min and reconnecting.....thought it was fixed, as then the fault message and yellow triangle had cleared, and it showed "ready". It then started and ran....for about 5 seconds! Put it in drive and it started to move. But then the ice eng. shut down and check hybrid system warning was back on.
    I Read somewhere that pulling white wire in fuse box for two minutes would reset everything and maybe fix it. This i did....it ran ok for all of ten seconds and had the same system shut down. I connected mini vci/ techstream. Did hybrid control system check, and there is only one dtc set: P0A0F, which is "engine failed to start". But it did.... and sounds entirely normal! Is this maybe a clue as to nature of failure? Perhaps the ecu that is monitoring engine status is shutting the whole sytem down because it has failed to sense signal that the engine is running? And i cant understand why Techstream cant diagnose the problem further than that. Like give more codes to guide me to the specific problem. Right now i just have A meter /dmm and techstream. Have to order the best repair manual i can get for it soany ideas what. i have the best chance of repairing this car myself rather than paying toyota dealer up the nose for repairs.
    Its funny....i had just taken cap off of inverter coolant to observe if any ripples in fluid indicating that coolant is being circulated, and i could see that the pump is circulating ok. I shut off engine for a few minutes after after checking this, and a few minutes later this failure occured. Any ideas what i can check?
     
  2. bisco

    bisco cookie crumbler

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    is there gas?

    is there a snowflake to click on for sub codes?
     
  3. PriusCamper

    PriusCamper Senior Member

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    Any signs of the engine running rough prior to this problem? And chance you bumped anything when taking the cap off inverter coolant?

    As for the engine running only 5 seconds, that's near the amount of time the hybrid battery would spin the engine to start it and then giving up because it didn't start. So the engine not starting would be the problem. Main problem with these Gen3 engines is EGR valve get clogged with oily exhaust and can lead to a blown headgasket if you don't clean that system and for preventative add an oil catch can.

    Keep in mind that you have a limited amount of time to start the engine before the HV battery is drained down too low to start engine and without the right gear recharging the pack will be a hassle, so be super thorough checking everything before you try to start the engine again.
     
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  4. Jim Caldwell

    Jim Caldwell Member

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    Yes it over 3/4 full. I did not notice any snowflake symbol. In the hybrid control sytem field. Does this appear right under the code or the "english translation" of code. Its new to me.
     
  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Prior to taking cap off inverter coolant reservoir it was running fine?
     
  6. bisco

    bisco cookie crumbler

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    i'm not sure. check some of the tech stream threads, there are screen grabs showing everything.
     
  7. Jim Caldwell

    Jim Caldwell Member

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    Yea prior to taking inv coolant cap off and dhring check and maybe a minute . after it was running fine. Then i shut it down. Perhaps 10 minutes later I attemped another start and then system went down, would not run as described.
    As for the snowflake icon when it was showing the one hybrid control system DTC: yes i checked and it was there. I clicked on it but it did not open up sub-dtc's to the "engine did not stsrt" dtc. It opens a data freeze-frame window. None of the parameters seemed useful. Some wrong...like engine rpm 900? When the car is not running at all?I did note that one parameter did not seem right. It showed "state of charge (all bat)" is 14.2%. If this is the charge status of the hv battery pak, there is something radically wrong. But there is no code set for bad hv battery pak!
     
  8. Jim Caldwell

    Jim Caldwell Member

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    I need to get really good repair reference i guess to have the slightest hope of figuring out what is wrong. Is a Bently manual sufficient or do you have to have the toyota tepir manualsthat toyota techs use. I dont know if they are available to the public or if i could afford oneif i could get the full manual.
    This is baffling, as how can any tech discover what part is bad from such a single generic code as "engine failed to start"? Has the health check really checked health of every 23+3 ecu's
     
  9. Jim Caldwell

    Jim Caldwell Member

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    Yes car was running fine. I bumped nothing else in engine compartment
     
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  10. Grit

    Grit Senior Member

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    Is this the same new Prius you bought, posted on another other thread?
     
  11. bisco

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  12. Jim Caldwell

    Jim Caldwell Member

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    A few times, like the time i tried to reset system. by pulling white wire out of fuse block for 2 minutes and then reconnecting it, the engine ran just long enough that i got it into FWD, and i moved car forward several feet before the hybrid system shut the car down. I have had a 2009 prius for 6 years, and so i know full well what a running ICE sounds like.....and i feel the strong vibrations as it starts and strong vibrations kind of like clunking when it shuts down too. Can also hear the inverter whine. But.... Looking at freeze frame data list for the hybrid control system, "state of charge (all bat) is reporting 14.2%. Is this the charge on the hv batt pak?
    And i've made many attempts to get car to run today.and the longest it ever ran was maybe 15 sec. I did charge up the 12v battery. Made sure it was well charged but it did not help or change behavior at all. I only get that one dtc for "engine failed to start". Is there a way perhaps to measure voltage of hv battery pak to see for sure if its down? I thought it was the 12v battery that spun up the ICE. So its really the hv batt pak, you're saying?
     
  13. Jim Caldwell

    Jim Caldwell Member

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    yea, same one.
     
  14. bisco

    bisco cookie crumbler

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    12v only boots the computers, closes relays, and runs a few accessories. hybrid battery and ecvt start/stop the engine thousands of times a day
     
  15. PriusCamper

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    So a sensor detects something AFTER the engine is running and shuts it down? P0A0F points to that problem, but doesn't go further than that... Hmmm...

    Seems like next step is to go into diagnostic mode in techstream where it spins up the engine and get as much data as possible if engine does or doesn't shut off. Then post what the data says about every detail of the engine when shut down occured. If it doesn't shut down perhaps the problem is related to when you try to shift it into gear? Again, techstream can harvest tons of info about what everything said at moment car engine quits... That data is where you're gonna figure what needs to be fixed.
     
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  16. PriusCamper

    PriusCamper Senior Member

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    You don't need the manual, you got us... Besides the terms of service for PriusChat participation requires that you promise to not read your owner's manual or any other kind of manual for that matter. We'll tell you what to read... And if we don't, Google what we already told other people on here to read for that specific problem. :)
     
  17. Mendel Leisk

    Mendel Leisk Senior Member

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    Just uneducated advice, and I'm not the first to say, I think you've got to desist from that. It's like trying to get a guy with broken leg to walk. And the process is running the hybrid battery down.

    If this happened immediately after checking the inverter coolant, it sure seems more than coincidence. What prompted that check; were there some symptoms, or was it just a whim?
     
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  18. TMR-JWAP

    TMR-JWAP Senior Member

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    You're seriously depleting the hybrid battery, so you're about to be in a real bind. I'm surprised it's still strong enough to spin the engine. Every time you disconnect the 12v battery, the HV battery SOC in the ecu goes to a default value around 60%, but unfortunately, it's probably much less than that. defaulting to 60% allows it to try to start the engine again. BUT, what really happens is you severly deplete it because it was really only 30 or 40%. Now it's even lower. Disconnect the battery again, and the cycle starts again, but now your real SOC is 20% and so on, until the HV battery is DOA.

    An engine needs three things. Air, Fuel and Ignition.

    Is there fuel pressure? A full tank isn't worth a dang if the pump isn't pumping it.

    Sometimes disconnecting the 12v battery can cause more problems. It tends to make those "learned values" in the ecu go back to default values. In a Gen 2, this sometimes causes the engine to not start due to the throttle body being out of range from expected. As buildup occurs on the TB interior, the throttle blade may not return to the "when new" position. The car learns this. Goes back to default, looks for "new" position, but TB is actually in the "crud build up" position. Sometimes all it takes on a Gen 2 is a good cleaning.

    Check to make sure the MAF sensor is clean. There's been instances of it getting dirty after banging an air filter housing and preventing engine start.
     
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  19. Jim Caldwell

    Jim Caldwell Member

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    Is there a way i can check voltage of hv batt pak with fluke? Without having to take rear seat out to access it? If "state of charge (all bat)" is the hv batt pak, then since its showing 14.2%, yea it going to read quite a lot less than 220v, right? Maybe the 12v batt is suddenly failed? I see how to check it on the mfd. What is normal voltage?
    I dont yet have a clue how to capture data as to what is happening at the moment when ice and the whole system shuts down. I wonder if O Reilly will take that 200.00 12v battery back if i replace it and it doesnt fix the hybrid system failre?
     
  20. Jim Caldwell

    Jim Caldwell Member

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    I have had a 2009 prius for 6 years. So i knew about the importance of inverter coolant pump working. It failed on my 2009 prius, and i replaced it myself. So i was making sure the pump on the new prius is running to prevent inverter failure. There was no symptom at all to prompt me to check. It was just P.M.
     
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