12 volt issues and disconnected vent tube

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by hippopotalust, Jan 27, 2021.

  1. hippopotalust

    hippopotalust Junior Member

    Nov 8, 2014
    2010 Prius
    I have a 2010 Prius that has been having 12-volt issues since it got cold out.
    It needed to be jumped about 3 weeks back, and then I noticed that sometimes it was fine, and sometimes the car had no "reaction" when I got into it or pressed the power button - none of the usual hum etc. In taking apart the trunk to get to the 12v it was jostled and then everything booted up as though there was no problem.

    About an hour ago, I went out to start the car and it hummed when I got in, but when I pressed the power button it did the typical fade on the dash screen that indicates 12v issues. Except after that, the check engine light turned on and the ! triangle flashed on and off. I got into the 12 volt in the back and noticed two things - the vent tube was completely detached from the battery and there was wetness in the underneath cavities the battery sits over. I reattached the tube and tried to start the car again. The ! triangle went away, as did the check engine, but the car did not start. The power button started flashing green (???). The entire time I was working on the car it was making the hum that indicates it was ready to start up.

    I think that there isn't enough oomph in the 12v to start it right now, but am wondering if
    1. The temps are affecting the 12v (temps have dropped from 48F yesterday to 18F tonight and it is snowing)
    2. If vent tube not being attached caused the issues I have been having with the 12v?
    3. If the wet was rain/snow (we get a lot) is getting in or something more sinister, and could be part of the problem?

    Car history: car was hit by a semi on the battery side, in 2019 - most of the damage was to the front and doors. Toyota did the repairs. Car has been driven pretty infrequently (once or twice a week most weeks) since the pandemic started, but since the jump start, have taken at least 8 20 minute interstate drives.

    Any thoughts?
  2. rjparker

    rjparker Senior Member

    Jun 6, 2008
    Texas Hill Country
    2012 Prius v wagon
    Have the battery load checked at any auto supply or dealer. Vent does not matter. Cold does matter on a weak battery. A Prius draws very little current from that agm battery. So when it gets flakey it means it has not been used for many days, there is a high parasitic load like a light left on, or most likely, it needs replacement.

    Not driving it frequently as described probably killed it. Buy a battery maintainer like the Battery Tender Jr for $28 to use with the battery in the future. But get the battery load checked first. No charger will fix a bad battery.
    #2 rjparker, Jan 28, 2021
    Last edited: Jan 28, 2021

    TMR-JWAP Senior Member

    Aug 12, 2016
    Columbia, SC
    2007 Prius
    That says a lot right there....faulty connection somewhere?
    Anything from a broken conductor internal to the battery, terminal connectors, ground wire fastener, plug in connectors