1. Attachments are working again! Check out this thread for more details and to report any other bugs.

auxiliary battery abnormally high positive voltage

Discussion in 'Gen 2 Prius Main Forum' started by pmmccabe, Dec 7, 2014.

  1. pmmccabe

    pmmccabe Junior Member

    Joined:
    May 31, 2012
    4
    1
    0
    Vehicle:
    2005 Prius
    Model:
    N/A
    2005 Prius shows a C1241 code, which can mean abnormally high or low positive voltage in the auxiliary battery. In my case it appears to be abnormally high, because my voltmeter showed the battery charged to 18 volts with the car off, and when running it showed 20 volts going to the battery. There's also a P0A80 code (hybrid battery pack) but I'm not convinced yet that it's a hybrid battery problem. Any ideas what would cause the overcharging of the auxiliary battery? Thanks.
     
    #1 pmmccabe, Dec 7, 2014
  2. jdcollins5

    jdcollins5 Senior Member

    Joined:
    Aug 30, 2009
    5,131
    1,338
    0
    Location:
    Wilmington, NC
    Vehicle:
    2010 Prius
    Model:
    III
    Within the Inverter/Converter module is a DC-DC converter that drops the 200+V hybrid battery voltage to 12-14.5V for charging the auxiliary battery and provide 12V to the car electronics. Normal aux battery charging voltage is 13.5-14.5V. 18-20V is abnormally high.

    It looks to me like you may have a failing DC-DC Converter. If so, that should be less expensive than the hybrid battery.

    Take it to your dealer and have them diagnose with the Sub Codes to go along with the DTC for a full diagnosis.
     
    #2 jdcollins5, Dec 7, 2014
  3. Easy Rider 2

    Easy Rider 2 Senior Member

    Joined:
    Aug 5, 2014
    1,584
    257
    0
    Location:
    Ocala, FL
    Vehicle:
    2013 Prius c
    Model:
    Three
    Unless that high voltage damages some of the other electronics in the car.....like the computer boards.

    IF he is sure his meter is relatively accurate, as tested by checking another 12 V battery for instance, I almost would recommend NOT driving the car with the voltage that high.

    Even if the converter is overcharging, the battery itself should not remain that high after sitting for a couple of hours.
    It is possible we have a bad meter here.......or operator error.
     
    #3 Easy Rider 2, Dec 7, 2014
    vskid3 and ftl like this.
  4. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,801
    48,998
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    how many miles on her?
     
    #4 bisco, Dec 7, 2014
  5. pmmccabe

    pmmccabe Junior Member

    Joined:
    May 31, 2012
    4
    1
    0
    Vehicle:
    2005 Prius
    Model:
    N/A
    Easy Rider 2 was dead on. When I checked my meter on a good 12v battery it showed 19 volts. Changed the 9v battery in my meter and the reading on the good 12v battery was back down to 13v. Then checked the charging voltage on my Prius and it showed 14.5 v. Thanks for setting me straight on that. Still have my dash warning lights though. I may try an inboard test of my auxiliary battery and see if it shows anything, then maybe it's a trip to the dealer. I appreciate your help -- learned something from both of you.
     
    #5 pmmccabe, Dec 7, 2014
    ftl likes this.
  6. pmmccabe

    pmmccabe Junior Member

    Joined:
    May 31, 2012
    4
    1
    0
    Vehicle:
    2005 Prius
    Model:
    N/A
    In response to bisco, 180,000 miles. Auxiliary battery is 4 years old next week. Replaced the hybrid battery pack with a rebuilt unit 14 months ago and have been getting top-end mileage (50 mpg) ever since.
     
    #6 pmmccabe, Dec 7, 2014
  7. jdcollins5

    jdcollins5 Senior Member

    Joined:
    Aug 30, 2009
    5,131
    1,338
    0
    Location:
    Wilmington, NC
    Vehicle:
    2010 Prius
    Model:
    III
    Good diagnosis !
     
    #7 jdcollins5, Dec 7, 2014
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,199
    6,464
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Check the ABS #1 and ABS #2 relays. Now that you have a properly functioning digital multimeter, remove each relay, one at a time. Apply 12VDC to the coil terminals (use the ohmmeter function to identify those terminals, the resistance should be ~ 100 ohms or so.) Measure resistance across the switched terminals, should be no more than 0.5 ohms after accounting for resistance in the multimeter leads. Replace the relay if it fails the test.

    You likely will have to replace the traction battery again in the near future given the presence of P0A80.
     
    #8 Patrick Wong, Dec 8, 2014
  9. Easy Rider 2

    Easy Rider 2 Senior Member

    Joined:
    Aug 5, 2014
    1,584
    257
    0
    Location:
    Ocala, FL
    Vehicle:
    2013 Prius c
    Model:
    Three
    Thank you. Experience is the best teacher, especially if you remember your mistakes.
    And I've made PLENTY of mistakes in the past.......and have a fair memory. (y)
     
    #9 Easy Rider 2, Dec 8, 2014
    jdcollins5 likes this.
(You must log in or sign up to post here.)