Error Code P0A08 (and others?) - Safe to drive?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by prius999, Oct 9, 2021.

  1. prius999

    prius999 Junior Member

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    Hello everyone, I have a 2009 Gen 2 Prius (98,500 miles) which has served me well for 3 years in my ownership here in the U.K. Today I got the Red Triangle Of Death unexpectedly and various other warning lights

    Screenshot 2021-10-09 194913.jpg

    Screenshot 2021-10-09 194846.jpg

    and on connecting my OBDII plug and using Dr. Prius I got the ECU error code 'HV Battery P0A08'.

    Screenshot_20211009-103941.png


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    The car still seemed to drive fine. On getting home (8 miles away), the Red Triangle was still present and Dr. Prius still showed the error code - turning the engine off and back on again got rid of the yellow warning lights, but the Red Triangle remained.

    I thought to connect my laptop and Techstream, but unfortunately before I did this I accidentally 'cleared' the error code with the Dr. Prius app by mistake! When I connected Techstream (v8), there was no sign of the P0A08 error code (which earlier posts on Prius Chat showed me was a 'DC/DC Converter Status Circuit' problem code), but it did throw up other current error codes, namely C1241 ('Low Battery Positive Voltage or Abnormally High Battery Positive Voltage' issue) from the ABS/VSC/TRAC system and B1421 which it tells me is a 'Solar Sensor Circuit (Passenger Side)' Air Conditioner problem. Hopefully the screenshots attached to this post will show you what I mean.

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    I am a bit of a novice when it comes to cars and electrics really, and beyond looking up the codes and researching as much as I can I am at a bit of a loss. I took the car on a 10 mile drive (having cleared the P0A08 error), and no more Red Triangle or other warning lights this evening, though the codes registered on Techstream remain (though without any warning from the car instrument panel). My Dr. Prius and Torque Pro apps on my Android phone are now showing no ECU errors at all, even though Techstream seems to be finding them.

    Is my Prius safe to drive? Should I get it checked out by an official Toyota garage? Are they going to rip me off for diagnostic fees? Any thoughts or advice gladly appreciated!! I've learnt a lot from this forum in the past 3 years, and am very grateful for any insight you can offer :)
     
    #1 prius999, Oct 9, 2021
    Last edited: Oct 9, 2021
  2. bisco

    bisco cookie crumbler

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    start with a load test of your 12v battery. how old is it?
     
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  3. dolj

    dolj Senior Member

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    You can park the B1269 for now as it is a historical code.

    The B1421 is not really a code that indicates a problem unless you read the codes outside in bright sunlight. It simply means bright sunlight not detected.

    One of the remaining codes that Techstream brought up - C1241 - needs to be read in conjunction with the P0A08 you accidentally deleted.

    The important code is the deleted P0A08. There are a few areas that need to be investigated as possible trouble areas.

    DTC: P0A08-264
    Detection Item: DC / DC Converter Status Circuit
    DTC Detection Condition: DC / DC converter malfunction
    Trouble Areas:
    • Auxiliary battery
    • Fusible link block assembly - HV control ECU
    • Fuse (for 12 V electrical equipment)
    • Engine room relay block
    • Inverter cooling hose
    • Water pump with the motor assembly (Inverter cooling water pump)
    • Cooling fan motor
    • No.2 cooling fan motor
    • Wire harness or connector
    • Inverter with converter assembly (DC / DC converter)
    While bisco's suggestion is good as it is first on the list to check so do that to cover all bases (don't ignore it), it is not likely at the heart of your issue but more collateral damage (see below).

    I say this because of what I can see in the freeze frame data of the C1241 you can see that car was travelling at 24 MPH so the car's 12 V system should have been powered by the DC/DC converter. If you look at the various 12 V voltages reported (IG1 voltage, IG2 voltage, BS1, BS2, VM1, VM2, +B1, and +B2) you can see that they report various voltages between 9.98 - 10.97 V which is well below what it should be. It also indicates the DC/DC converter was not working as it should.

    The one that probably is of concern is the BS2 voltage of 9.98 V and the one the system is most unhappy about.

    You need to work out why that DC/DC converter was not supplying the 12 V system as it should. When this happens, the small 12 V battery in the back is the backup and has to supply the power - until it can't.

    You will most likely need to charge up the 12 V battery as it has taken a beating by being run down to 9.98 V.

    You will see in the list of probable trouble areas is the inverter cooling water pump (ICWP). This is easy to check by putting the car into IG-ON mode (two presses of the power button with your foot OFF the brake) and then look for coolant movement in the inverter coolant reservoir which is next to (centre side) the inverter (silver box on the left side). If you see no movement, touch the ICWP to see if you can feel vibrations or hear it humming. If no movement and no sign of the pump working you have a failed ICWP. Easily fixed DIY and the OEM part is not too expensive.

    Let us know what you find and we can give more info if you have any questions.
     
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  4. prius999

    prius999 Junior Member

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    Many thanks for your reply. I have had the car since Dec 2018, and I haven't changed the battery myself since then, but I'm not exactly sure how old the battery is.

    I'm not sure if this is the load test you've mentioned? (I found this procedure elsewhere on PriusChat some months ago):

    "- Without brake pedal, press the Power button once and release to enter ACC mode

    - Press and hold the MFD Info button, then turn the headlights on and off three times to enter Maintenance mode; release Info button

    - Press “Menu” (on screen)

    - Press “Display Check”

    - Press “Vehicle Signal Check” - the battery voltage is shown and should be about 12.4 to 12.8 Volts (normal for an unloaded battery)

    - Again without brake pedal, press Power button and release to put a current load on the battery - the voltage should stay above 12.0V (if less than 12.0V the battery is not well, or there is a fault or unusual load somewhere)

    - Press brake pedal and press Power button once to enter "Ready" mode - the battery is now charging at about 14V (if less than 13.6V or more than 14.4 there may be a problem with the charging circuit)

    - Turn car OFF to leave Maintenance mode"


    If it is, then the battery was within normal range for the above instructions, showing between the suggested parameters in the post.
     
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  5. prius999

    prius999 Junior Member

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    Thank you for such a comprehensive response, and for taking the time to reply :)

    OK, so I've opened the inverter cooling water pump reservoir when the car is in IG-ON mode, and I couldn't see any movement in the coolant liquid, or hear any vibrations / noise. I was pleased to read your comment that if this does indeed mean that it's the ICWP as the culprit, it is an easy and inexpensive fix.

    I decided to book the Prius into my local Toyota dealer here in the U.K. as I am not too confident with a DIY repair (I am dangerous enough behind the wheel, let alone under the bonnet / hood), and, armed with the screenshot of the Dr. Prius app and so evidence of the deleted P0A08 code, I offered a thought to the technician that it might be the ICWP. I left the car with them today, but then when I picked it up, they told me that they couldn't find any error codes bar the B1421 one. (I hadn't given them the Techstream summary screenshot or the screenshot of the freeze frame data as I didn't think they'd look too kindly on my having unauthorised access to a Techstream setup.) The historial B1269 code was gone, and there was no sign of the C1241 code on the screenshot of their Techstream that they gave to me! I was baffled, but there was no charge for their diagnostic as they didn't actually find anything.

    I mentioned the ICWP and the lack of turbulence in the fluid, to which the technician said that there wouldn't be a massive amount of disturbance in the fluid and so I wondered if I'd been looking correctly or whether I should have looked more closely when I had a go myself. I have hooked the Prius back up to my older version of Techstream, and indeed the only code now showing is the irrelevant B1421 one. How is this possible? Shouldn't the previous C1241 still be present, even as historical if the car was no longer complaining about it?

    The technician advised me to drive it until the car told me to 'stop', but he was sketchy on whether there is a 'stop' light that will illuminate on the dash. He seemed to be saying that I can drive it OK with the Red Triangle on the dash, but that when / if the ECU error code recurs and the Red Triangle is present, to come back and book it in again. I am a little wary about this, especially as my wife has a 45 mile round trip to do tomorrow and I wouldn't want her 20 miles from home with a car that is playing up. Can I damage anything more seriously by waiting for the fault to reoccur and then booking it back in with Toyota?

    He said that the P0A08 code is not one that relates to anything on his system, and is in his view a generic code that might be called something else in the Toyota software that he uses (I had written P0A08: DC / DC Converter Status Circuit on the sheet of paper with the Dr. Prius code screenshot).

    Any thoughts on the above that you might have would again be most gratefully received; I am trying to learn quickly and apologies for any newbie naivety :)
     
  6. bisco

    bisco cookie crumbler

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    there is no stop light, i hope he meant if you get a trouble light, or if the mfd says to stop driving and pull over in a safe place.
    since you cleared the codes with doc prius, they wouldn't show up for the dealer. they will come back eventually though.

    the inverter fluid will have noticeable movement vs perfectly still.

    to load test the 12v, connect doc prius and read the voltage. then turn the headlights on and watch the voltage sag over 15 minutes.
     
    #6 bisco, Oct 15, 2021
    Last edited: Oct 15, 2021
  7. ChapmanF

    ChapmanF Senior Member

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    That's nuts. As dolj pointed out, the car is driving at 24 MPH, so obviously in READY, meaning the DC/DC converter is supposed to be online, but voltages below 11 V are recorded in a freeze frame, and somehow this mechanic thinks a P0A08 code (which means "the DC/DC converter has malfunctioned, entered a fail-safe mode, and the aux battery voltage has dropped below 11") is generic and doesn't relate to anything? Unreal. :rolleyes:
     
  8. Mohammed Tubaishat

    Mohammed Tubaishat New Member

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    Hey guys i have Camry 2013 hybrid ,
    My car shows a check hybrid system
    P0A08 from 2 years :) , nothing seemed to be not working, everything works fine ( i never faced an issue with the vehicle power at all)
    I changed the inverter but same problem still , and tested the 12v battery and changed the hybrid battery from the dealer
    Please help!
     
  9. prius999

    prius999 Junior Member

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    Thanks bisco, I will carry out this test once I get the car back - the warning lights have come on again and I've taken it back to the garage
     
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  10. prius999

    prius999 Junior Member

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    I think the problem was I couldn't show the tech that I've got some Techstream freeze frame data, as of course I shouldn't have access to that software really I guess. He said that there were no codes showing up on his system when he tested it, but (fortunately?) I now have the warning lights on again and so have taken it back to the garage. I will be interested to see waht they diagnose this time!!
     
  11. ChapmanF

    ChapmanF Senior Member

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    I'm pretty sure my local dealer guys have guessed I'm not a Techstream virgin, and they haven't sent the Dementors around.
     
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  12. prius999

    prius999 Junior Member

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    Posted via the PriusChat mobile app.
     
  13. prius999

    prius999 Junior Member

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    Just to update - I showed the Techstream data to the Toyota guys in the end, and they remarked too that the battery was low. They couldn't get any codes (apart from the aircon one), from the system though and after testing it extensively they have decided it doesn't need any work.

    I'm a little bit miffed about this, though I've done a few days driving in the car now and all seems fine (no warning lights or Red Triangle). Do the codes I've submitted above just clear up of their own accord sometimes? Good news is that Toyota didn't charge me for any of the diagnostic work they did, so I am not out of pocket.

    Thank you for your suggestions here over the last fortnight :)
     
  14. bisco

    bisco cookie crumbler

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    if everything is working, just ignore it
     
  15. bisco

    bisco cookie crumbler

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    perhaps an intermittent grounding problem. check the 12v connections for cleanliness and tightness, especially negative to ground.
     
  16. prius999

    prius999 Junior Member

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    Posted via the PriusChat mobile app.
     
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