Solution to 12V issues? Disconnect 12v negative terminal sensor plug

Discussion in 'Gen 5 Prius Main Forum' started by Halcykon, Dec 1, 2025 at 11:28 AM.

Page 2 of 2
  1. Brian1954

    Brian1954 Senior Member

    Joined:
    Jan 31, 2021
    2,185
    854
    0
    Location:
    South Central PA, USA
    Vehicle:
    2011 Prius
    Model:
    III
    Did you make a typo for the year? Did you mean 2026?
     
    #21 Brian1954, Dec 2, 2025 at 10:11 AM
  2. VelvetFoot

    VelvetFoot Active Member

    Joined:
    Sep 17, 2025
    609
    212
    0
    Location:
    New York State
    Vehicle:
    2026 Prius
    Model:
    LE
    Yes I did. Thanks for picking it up. I was able to change it.
     
    #22 VelvetFoot, Dec 2, 2025 at 10:48 AM
    Brian1954 likes this.
  3. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    35
    19
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    Can you link the video? I'm not familiar with triple tapping or what the rationale is behind putting the car in ready.
     
    #23 Halcykon, Dec 2, 2025 at 1:27 PM
  4. Gokhan

    Gokhan Senior Member

    Joined:
    Oct 5, 2008
    6,182
    2,441
    0
    Location:
    Paramount CA
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    Yes, that can be done (idling in READY for an hour). You would have to do that every week. A battery maintainer is the way to go though, but you need a garage.
     
    #24 Gokhan, Dec 2, 2025 at 1:27 PM
    GcinFl and Halcykon like this.
  5. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    35
    19
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    Good to know that there are more datapoints for this! How did you come to the conclusion for that with your F150?
     
    #25 Halcykon, Dec 2, 2025 at 1:28 PM
  6. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    35
    19
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    What is that knob called? I'm currently thinking of some aftermarket solutions for disconnecting the 12V when I can't use a trickle charger.

    This knob, or some sort of quick release mechanism, would be great.
     
    #26 Halcykon, Dec 2, 2025 at 1:29 PM
  7. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    113,953
    51,892
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    vehicle battery isolator quick disconnect, amazon et al:
    [​IMG]
     
    #27 bisco, Dec 2, 2025 at 1:34 PM
    GcinFl and PriusCamper like this.
  8. BiomedO1

    BiomedO1 Senior Member

    Joined:
    Mar 27, 2021
    3,556
    1,843
    0
    Location:
    SacTown, Ca
    Vehicle:
    2021 Prius Prime
    Model:
    LE
    Ok; I just did a quick test. This is by no means a real test, don't have a BM2 to do a long term test.

    1. my battery was 11.8VDC, so I placed a 6A battery charger on it for two hours and disconnected the sensor
    2. battery check was 12.8VDC now, so placed the car into Ready mode; meter shot up to 14.2VDC - No CEL, 5 minute test.
    3 . Shut-down and reconnected the sensor, battery @ 12.4VDC - Got the car back into Ready mode - 14.1VDC for another 5 minutes.

    I'll need to get a BM2 to chart the charging voltage as the car is running, but disconnecting that sensor doesn't trip the CEL. Since there wasn't a significant change in the DC-DC converter over either 5 minute test interval - I can't really say if it's working or not; just that it doesn't trip the CEL on a gen4.
     
    #28 BiomedO1, Dec 2, 2025 at 8:58 PM
    futurist and jbbass like this.
  9. VelvetFoot

    VelvetFoot Active Member

    Joined:
    Sep 17, 2025
    609
    212
    0
    Location:
    New York State
    Vehicle:
    2026 Prius
    Model:
    LE
    It could also be possible to check the voltage while running with OBD Fusion or Car Scanner over CarPlay (Gen5). Possibly charting as well.
     
    #29 VelvetFoot, Dec 2, 2025 at 9:14 PM
  10. soft_r

    soft_r Active Member

    Joined:
    Feb 25, 2024
    176
    139
    4
    Location:
    Beverly Hills
    Vehicle:
    2024 Prius
    Model:
    LE
    Never dropped below 14v for me after disconnecting. Stayed between 14-14.1v.

    No CEL.

    I'm thinking I'm gonna leave it disconnected as my OEM battery shat the bed after a year (11.6v resting voltage on a 20F day after no driving for 2 days; car still started fine and no errors but I didn't like that and swapped to an AGM). Maybe it was a bad battery, maybe it was the BMS shenanigans, don't know don't care. Going with the safe route: BMS disconnect + AGM.
     
    #30 soft_r, Dec 2, 2025 at 10:36 PM
(You must log in or sign up to post here.)
Page 2 of 2