P0A08 and I have to pee! Can I drive at all?

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by PriusPaddler, Jun 30, 2026 at 2:12 PM.

  1. PriusV17

    PriusV17 Active Member

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    I would just change the 12v first. 9 years is long considering typical lifespan is 5 years. That code's primary cause is a very weak 12v battery. I'm changing my 12v quite frequent. Because once it's drained, it's damaged and not the same. I'm now on the 12v Sodium Ion version. Just the switch alone reduced 20lbs of weight. So far pleased with the switch. If I have to reset the battery it's just a button on the battery.
     
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  2. PriusPaddler

    PriusPaddler Member

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    I understand that idling in heat will be hard on a car... this time was not planned, just was mixed up schedules between my son and I meeting to move him out of an apartment and I did some work in the car waiting for him. I'm just curious how the people who camp in their prii handle that? With my 2009, I remember choosing to sleep in my car once vs setting up a tent at 11pm, but it was so hot out (in SD in September it was over 95 degrees) that I ended up rolling up windows and sleeping with A/C on. That would have been 5 hours or so... maybe I just got lucky.

    So - sounds like I'm headed to a dealer no matter what. Exactly what I was hoping to avoid. $230+tax just to walk in the door and that amount of money is hard for me... but of course as you point out, better than damaging entire engine. I guess I need to encourage one of my mechanically inclined children to get certified!

    I did tell them to move forward replacing the original 9.5-year-old Yuasa 12v battery.
     
  3. PriusPaddler

    PriusPaddler Member

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    I had them proceed - they were kind of astonished, given the car was put into service in late 2016. That needed to be done even if it doesn't solve anything else. Glad you like your new one. Hopefully you don't have reason to reset it often.
     
  4. Brian1954

    Brian1954 Senior Member

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    The shop is not using Techstream, but it looks like a good scanner. It was able to scan 20 different ECUs.

    The first three codes are the ones to concentrate on fixing. I will try to find the service manual for those and post links in a later post.

    Did you check the engine coolant level in the plastic reservoir? Have you added coolant?
     
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  5. PriusPaddler

    PriusPaddler Member

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    I have personally never had to add coolant. I only checked the small reservoir for the inverter coolant, but the shop said they checked both and it was fine.
     
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  6. rjparker

    rjparker Tu Humilde Sirviente

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    The B1503 means the coolant temperature sensor downstream of the exhaust heat exchanger exceed 248f. Normal it is around 195f, typically not exceeding 210f even under high load.

    v red 2of2  exhaust recirc temp vs green engine temp.jpeg

    Often the engine coolant temperature does not code, perhaps because the exhaust heat exchanger sensor codes first and the system starts shedding loads.

    Two causes are typical, one is the main water pump or thermostat has failed or is weak or second, the exhaust heat exchanger is stuck in a mechanically controlled fast warm up mode.

    Often normal shops don't know an exhaust heat exchanger exists much less are reading its live data.

    The typical advice is to bypass the exhaust heat exchanger and see what happens next. Repair by the book is replace it which can be $2k or more. Bypass is the better diagnostic move and in most states is no problem long trrm.

    Monitoring these temperatures while driving with the ac on can be helpful and your shop could do it.

    IMG_1982.jpeg IMG_1981.jpeg

    Others who have had this code found the engine temperature sensor remained normal but the exhaust heat exchanger caused issues. With your "too hot to touch hood", etc it may be more fundamental whole engine overheating.
     
  7. rjparker

    rjparker Tu Humilde Sirviente

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  8. rjparker

    rjparker Tu Humilde Sirviente

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  9. PriusPaddler

    PriusPaddler Member

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    Here is the latest word on AC from mechanic:

    "I checked both the pressures in the AC system and I believe that the system is overcharged. Therefore, at idle the pressure gets too high and the system shuts down. Cleaning the radiator is recommended, might help, but does not fix the underlying overcharge situation. We can do the cleaning first and see if it gets us close enough or not. And it needs to be done regardless. Other possibilities exist, but all further AC diagnostics require starting with a known properly charged system so it is our first step after the radiator cleaning. Short term, you can leave it, but it is stressing out the compressor."

    EDITED TO ADD - I have never charged or recharged the AC, so it has gone 45k miles "as is" from the dealer in January 2025. Problem at idle started this year, whenever Minnesota warmed up.

    And on overheat:

    "I believe the code and overheating hybrid cooling system is due to a failing water pump. I can't prove that."

    Sooooo. New 12v battery is in... *** Do I move on with either evacuate and recharge the AC? or the radiator clean (they say they have adapted a tool to do this well, but still charge a couple hundred $$)? And hope that whole improvement reduces the chances of overheating?

    First three codes are P0171 (never saw that before myself - could be gas or O2 sensor maybe?), P0A08, and then B1503 (also I've never been able to read that before).

    I like the approach of fixing one thing and then seeing the fallout before moving forward. BUT I'm not sure swapping 12v will be the end of it - what would be the next logical step? Hard to say if I have one problem or two... (or more)

    Do I get the car back and drive without AC and see if it ever overheats again? Or fix the AC and then wait and see? I do a LOT of driving on rural highways where I will be pretty good and stranded if it gives out on me. Not sure how long I can last without AC either - I start melting, lol.
     
    #29 PriusPaddler, Jul 1, 2026 at 5:11 PM
    Last edited: Jul 1, 2026 at 5:20 PM
  10. PriusPaddler

    PriusPaddler Member

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    @rjparker I was typing while you were. I will digest your posts and read the links. Thank you.
     
  11. rjparker

    rjparker Tu Humilde Sirviente

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    You did not see the codes because Dr Prius is not that good for most codes.

    Fix the ac charge first. Cleaning the outside of the condenser is logical. Delay "cleaning" the radiator or a radiator drain and fill. No 12v battery unless it fails a load test.

    He is guessing on the water pump and apparently does not know the b1503 is pointing to the exhaust heat exchanger.

    Engine water pump is good preventative maintenance but only if he uses an oem pump. Aftermarket pumps fail quickly.
     
    #31 rjparker, Jul 1, 2026 at 5:23 PM
    Last edited: Jul 1, 2026 at 5:31 PM
  12. PriusPaddler

    PriusPaddler Member

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    He was proposing cleaning radiator FINS I think... not necessarily drain and fill... is that helpful at all? It could be full of the guck in the air or dog fur that floats around my yard like clouds.
     
  13. Brian1954

    Brian1954 Senior Member

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    Why does the mechanic think the hybrid cooling system is overheating? The B1503 code is on the separate engine cooling system.

    The P0171 lean code is usually a leak at a vacuum hose. A scanner that can read live data is very helpful on fixing the problem.

    I agree that the AC should be fixed first.