Is it my 12v or my Hybrid battery?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Rebelcrypt, Jan 9, 2026 at 6:10 PM.

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  1. Rebelcrypt

    Rebelcrypt New Member

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    Vehicle:
    2008 Prius
    Model:
    Base
    Hello there,

    I have a 2008 Prius, 180,000 miles. Car was working fine, and 2 days ago I start it up and I get the red triangle, check engine, vsc, and ((!)) lights on. Turned it off and left it, and went back today to see what's going on. Turned it on again, same lights, and I decide to try to drive it. I drive it up the road to O'Reilly's to get the check engine read. Its driving fine there and back. The reader brings back the code "P0AFA Hybrid/EV Battery System Voltage Low". I call up the dealership and they said its likely the hybrid battery needs to be replaced, quoting $4,000. After looking around online, i decided to just check the 12v. I view the vehicle signal check on the dashboard and it reads 11.5v. When I turn the car on and drive it, it reads 14.1v. I drive it back up to O'Reilly's to test the 12v and they said it looks like the 12v is good but its drained and needs to be charged. I drive it around the neighborhood for a bit to try to charge it. I check the vehicle signal check in the dashboard again and it reads 12.2v but then drops to 11.8v in about 5sec, dashboard lights are all still on. So now I'm wondering if its the 12v instead of the hybrid. Since its reading under 12v at rest, is it more likely that its the 12v and not the hybrid?

    Note1: I had the 12v replaced by AAA a little under 2 years ago. I've only just now seen some posts on here that they have shit batteries.

    Note 2: I have a Bluetooth OBDII reader coming tomorrow and plan to look at the hybrid battery through the Dr Prius app, but not sure if that will actually help me diagnose the problem since its my first time trying that out.

    Thanks in advance for any help
     
    #1 Rebelcrypt, Jan 9, 2026 at 6:10 PM
    Last edited: Jan 9, 2026 at 6:20 PM
  2. priumium

    priumium Member

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    Location:
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    Vehicle:
    2013 Prius Plug-in
    Model:
    Plug-in Advanced
    Hello there!

    Unfortunately, the P0AFA Hybrid/EV Battery System Voltage Low is related to your hybrid battery. It has nothing to do with your 12V health, which btw also seem to need attention/replacement…. It should not drop below 12V ever, if capable.

    Don’t waste your time on 12V focus. That is easy to fix.

    Focus on evaluating avenues for fixing the hybrid battery, there are many.
     
    #2 priumium, Jan 10, 2026 at 9:49 AM
  3. BiomedO1

    BiomedO1 Senior Member

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    Location:
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    Vehicle:
    2021 Prius Prime
    Model:
    LE
    Put the 12v battery on a battery charger, to fully charge it - then retest it. In my experience, you usually don't get phantom error codes until your battery gets down to around 10.5 VDC. If your battery can't handle a load test, it can dip below that 10.5V threshold and cause intermittent issues.
    FWIW; your probably getting 'crap' mpg with a weak traction battery and your engine will surge while trying to push more electrons into that traction pack. This is also the reason you can't simply drive the car around to recharge your 12V battery. These cars are bias toward pushing as much electrons as it can get, back into the traction pack.

    Hope this helps....
     
    #3 BiomedO1, Jan 10, 2026 at 12:51 PM
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