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Red Triangle/Red Battery/Red Car icons + 10.9v 12v

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by azgen2, Sep 16, 2024 at 5:29 PM.

  1. azgen2

    azgen2 Junior Member

    Joined:
    Aug 9, 2021
    1
    0
    0
    Location:
    USA
    Vehicle:
    2007 Prius
    Model:
    N/A
    I've had an 07 since 2018 that's been great minus an ABS actuator replacement I diy'd a few summers ago, but it's been acting up lately. I had my power brakes 'go out' a couple months ago, which ended up being my fault, brake fluid was below the low line and I didn't notice it. I got that refilled and it was fine and then a week later it lit up with warning lights and I read them manually with the blinking system and saw C1241 (Low Battery Positive Voltage or Abnormally High Battery Voltage). I checked my 12v voltage and sure enough it was sitting around 10.8-11v while checking through the touchscreen menu you can get into that will read the voltage.

    I had oreillys test that battery, which I had bought from them a few years earlier, and they said it looked fine and just needed to be charged up. I was sick of dealing with it and decided I'd just buy a new 12v battery from Toyota to ensure the 12V wasnt going to be an issue. That was about 2 months ago. It was fine until today when I went to start it up and got the red triangle + the red battery icon, the car with the ! icon, and a check engine I believe. I have an MX+ bluetooth OBD2 scanner coming in later today, so I cant read any codes yet but will post what I find. Haven't had any issues with the hybrid battery discharging fast/not charging up how it normally does/etc but we will see if it's having issues when I can read the codes.

    One thing I did notice is that my new 12V is reading 10.8-10.9v when checking it through the touchscreen menu again. It drops to 10.1v when the headlights are turned on and jumps to 14.4v when the cars turned on, so it is at least getting a charge. However, I read the 12v voltage manually with a multimeter and was getting a low 11.5V reading, but when jumping into the car and testing it through the menu, it shows 10.8-.9 volts. Not sure if the discrepancy is normal.

    Any ideas here? I havent been making longer drives in the car, usually around 5-10 miles at a time multiple times a week ever since it started giving me problems. I dont trust it on longer drives and have been using a different vehicle for those. Prior to all these issues, I was putting around 600-900 miles a month on it. I dont know if the shorter trip duration is not fully recharging the battery (may need to buy a charger and juice it up once a month?) and/or I got unlucky and got a faulty 12v or if something else is going on.

    Obviously the codes will help a lot, but wanted to brain dump this and will update it when I have more info. Thanks!
     
  2. MAX2

    MAX2 Member

    Joined:
    Aug 12, 2024
    301
    66
    6
    Location:
    Third Rock from the Sun
    Vehicle:
    2007 Prius
    Model:
    N/A
    After the car is turned on, the 12V auxiliary battery starts to consume powerful consumers.
    There is a small drop in voltage from 12.2 to 11V or even less.
    After the "ready" sign appears on the dashboard, the hybrid system is turned on, which begins to recharge the auxiliary battery.

    It is important to understand that a 12V battery, when discharged to 10V or less, can temporarily drop to these values, and when starting the car, error checks may pop up, which are not critical, but may indicate low voltage.
    This does not apply to a high-voltage battery.
    If it becomes inoperative, there will be many more emergency checks and icons on the panels and you are unlikely to see the "ready" sign, and in this case, the car will not start the engine.