New Yellow Top Accessory battery, but still have voltage issues

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Dbedard67, Sep 1, 2014.

  1. Dbedard67

    Dbedard67 New Member

    Joined:
    Sep 1, 2014
    2
    0
    0
    Location:
    Florida
    Vehicle:
    2008 Prius
    Model:
    N/A
    Hello,

    I was driving home and the dash lit up like a Christmas tree. I read here that the accessory battery was likely the cure for my Prius' symptoms, which included:
    red triangle
    brake light
    brake warning light
    "Problem" on touch screen with a little picture of a car with an exclamation point.
    Slow wipers
    Air conditioning intermittent

    My 2008 Gen II has 230,441 on the odo. The new battery came in at 14.1 volts on the touch screen diagnostics before I drove it.

    Today I changed the accessory battery and everything cleared and it looked promising until I took it for a 15 mile road test. After a while all the symptoms came back.

    I used the touch screen display trick to get into the diagnostics and the voltage was slowly dropping while I drove. Turning things on made it worse.

    Do I need to change the alternator? Does the Prius even have one? Anyone else have this issue?
     
    #1 Dbedard67, Sep 1, 2014
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    112,128
    51,023
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    did you test the optima before installing?
     
    #2 bisco, Sep 1, 2014
  3. Dbedard67

    Dbedard67 New Member

    Joined:
    Sep 1, 2014
    2
    0
    0
    Location:
    Florida
    Vehicle:
    2008 Prius
    Model:
    N/A
    No, but it read 14.1 volts (engine off) on the touch screen before I drove it.
     
    #3 Dbedard67, Sep 1, 2014
  4. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    112,128
    51,023
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    hmm, i would throw a voltmeter on it in the morning before starting the car, unless someone has a better idea. i suppose it could be anything at 230k. the prius uses a dc to dc converter to keep the 12v charged from the hybrid battery. welcome to priuschat btw!(y)
     
    #4 bisco, Sep 1, 2014
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,200
    6,491
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Check the inverter coolant reservoir for fluid turbulence when the Prius is READY. If you do not see this, the inverter coolant pump has failed and that is the root cause of your car's problems. When the inverter overheats, the DC/DC converter shuts down which causes voltage on the 12V bus to sag since the 12V battery is now called upon to power all of the electrical circuits. The battery has insufficient capacity to do this very long so the voltage drops which causes various ECUs to log DTC and turn on the various warning lights that appeared.

    The slow wiper motion is another clue that the inverter is overheating - 12V bus voltage is lower than normal. A further clue is the intermittent AC compressor operation which is due to the inverter overheating and shutting down the three-phase AC power to the compressor.
     
    #5 Patrick Wong, Sep 1, 2014
  6. nh7o

    nh7o Off grid since 1980

    Joined:
    Dec 10, 2011
    1,686
    340
    0
    Location:
    Hawaii
    Vehicle:
    2009 Prius
    Model:
    II
    No alternator in the Prius.
     
    #6 nh7o, Sep 2, 2014
(You must log in or sign up to post here.)