2008 Prius Breakdown - 4 Codes: P1121 P0420 P0A80 P3012

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ChunkyLover53, Aug 23, 2025 at 1:22 AM.

  1. ChunkyLover53

    ChunkyLover53 New Member

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    Albuquerque NM
    Vehicle:
    2008 Prius
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    Hello all,

    First post on the forum, but long time Prius owner, had a 2007 prius for several years until an accident and then replaced that one with my current 2008 Prius a couple years ago, it has about 120,000 miles on it and as far as I know the HV battery is original, the cat converter was stolen at one point and replaced.

    Has been driving fine then all of the sudden this morning on the way to work the Prius went bonkers and threw these 4 codes along with the red triangle of death.

    The HV battery fan turned on in the back, and the prius could barely drive, I'm guessing this was a fail safe mode, I was able to limp it a couple miles back home, but it barely would go over 15 to 20 miles an hour and the accelerator pedal wouldn't do anything which is odd - the vehicle would move forward at 15 to 20 mph with no pressure on the accelerator pedal, fortunately the brake pedal still worked.

    These are the codes my matco MD60 OBD scanner read out (this is all I've got at the moment, but sounds like there are better code readers / apps out there that can tell you more info and specifics on the HV battery)

    • P1121 - Coolant Flow Control Valve (my reader called it an "Accelerator Pedal Position Sensor problem" but I don't think that description is correct, it should the coolant flow control valve)
    • P0420 -Generic Catalyst System Efficiency Below Threshold (Bank 1)
    • P0A80 - Generic Replace Hybrid Battery Pack
    • P3012 - Battery Block 2 becomes weak
    Anyway, I'm wondering how screwed I am here. Did the HV battery and catalytic converter both just decide to catastrophically fail this morning or could it be as easy as the coolant flow control valve have broken and replacing it would fix the other codes because coolant isn't flowing through the system causing all the codes to trigger?

    Any input is appreciated.
     
    #1 ChunkyLover53, Aug 23, 2025 at 1:22 AM
  2. Brian1954

    Brian1954 Senior Member

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    If you want to keep this car, the hybrid battery needs to be replaced or repaired. That will fix the P0A80 and P3012 trouble codes. After that, you can then work on fixing the other two codes.
     
    #2 Brian1954, Aug 23, 2025 at 4:20 PM
  3. Dion Kraft

    Dion Kraft Member

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    Vehicle:
    2004 Prius
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    Base
    P1121 is an error at the Coolant flow Control valve. Usually it means that the ECM could not command the gear within the valve case to move or rotate. Check out my post in: Gen 2 technical discussion - Water Valve controller disassembly - of this valve and how it works if you are interested.
    AND Welcome aboard by the way!
     
    #3 Dion Kraft, Aug 24, 2025 at 12:09 PM
    Last edited: Aug 24, 2025 at 12:15 PM
    Brian1954 likes this.
  4. rjparker

    rjparker Tu Humilde Sirviente

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    Three
    Sounds like you have three problems. Might be time to decide if that car is a keeper or not. The battery fan increased speed because the battery was overheating.

    The P0420 code probably was there already and is due to the aftermarket cat. I don't think it caused your limp mode. Most likely the hybrid battery is way past due.
     
    #4 rjparker, Aug 24, 2025 at 12:26 PM
    Last edited: Aug 24, 2025 at 12:47 PM
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