12-volt Auxiliary Battery Going the Way of the Dinosaurs?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Zedhomme, Dec 26, 2013.

  1. Zedhomme

    Zedhomme Member

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    Prius Chat colleagues. Now it's my turn. Merry Christmas.
    Just want some confirmation or denial of my suspicions.
    Background: My 2007 Prius Touring, 135,000 miles, 12-volt battery is 4 years old and has 100,000 of those miles.
    The positive-Very trouble free 7 years and 135,000 miles with just basic maintenance and things Toyota has replaced under Warranty, LSC and T-SB.
    Original 12-volt died soon after 30,000 mile warranty expired.
    Have NOT noticed any anomalies in the charging/discharging cycle of the hybrid battery or braking.
    After a short drive in the dark this morning, very cold temperatures, turned on the car. Master warning light, brake system warning light, Vehicle Stability Control System warning light (VSC), Malfunction Indicator lamp (Check Engine), Hybrid System Warning Light all came on. Already suspecting the 12-volt battery, so I proceeded to drive home with no noticeable change in performance.
    Tested 12-volt with the following results: at Jump Start Terminal - 12.5 volts; at Battery Terminals - 12.2 volts; Readings in diagnostic Mode - 11.9 volts, then turned on dropped quickly to 11.7 when turned on.

    Have I gained enough knowledge here on Prius Chat to be correct in thinking my 12-volt battery is starting to go the way of the dinosaurs?
     

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  2. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Hey Zed,
    At this point, its too early to tell. I wish you had a scanner and could read the codes. The readings you posted aren't terrible. If I were in your shoes, I would head to the local Auto Parts Store and purchase a battery charger/maintainer, hook it up until the battery is fully charged, disconnect and reconnect the negative lead on the battery and see if your lights come back.

    The fact that your car drove fine with no noticeable decline in performance is a good sign.
     
  3. The Electric Me

    The Electric Me Go Speed Go!

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    In a way, I'd say it doesn't matter from the standpoint that if the aux battery is 4 years old? Probably a real good idea to change it anyway. Even if it is premature to actual failure, that battery can't have too much more life left in it.

    So I'd say, your suspicion is highly justified, and the only real way to know, is to replace the aux battery and see if it solves your problems.

    If it doesn't? The money spent on the aux battery wasn't wasted, you were probably close to needing it one way or another.
     
  4. Zedhomme

    Zedhomme Member

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    Thanks shipmate (usnavysgtc). I have a mini-VCI en route because I plan on driving it until about 250k and want to be able to check the HV modules individually. For this problem it's just a day late as they say.
    I thought about the charger/maintainer, but that's $50 towards the new battery I don't really need to spend.
    I did disconnect the battery, waited about a minute, reconnected and restarted and no lights of any kind.
    Haven't driven it far yet. Having a Prius mechanic buddy check on a 12-volt price for me.
    With these months and miles on it I know it's days are numbered and with a daily commute of 70 miles round trip to work, it's just not worth waiting for it to inconvenience me while going to/from work.
     
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  5. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    I for one sincerely believe that regardless of how long you wait your 12v battery will not turn into petroleum.
     
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  6. Zedhomme

    Zedhomme Member

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    Tony. Don't quit your day job, unless of course it's standup comedy. So, my analogy may not have been the best, but I meant they are both dead.
     
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Its unclear that the 12V battery is the problem.


    What is the voltage across the 12V battery, when the Prius is READY?
     
  8. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    I tend to agree that at this point, the 12v battery cannot be pinpointed as the problem. More testing is def necessary and yes, good call Patrick to measure the voltage when in READY.
     
  9. Zedhomme

    Zedhomme Member

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    OK. Just got back from a test ride. Left the headlights off and fan, drove around town with multiple stops running errands and had no lights pop up. Saw you reply and tested the 12-volt in READY. Putting out 13.9 volts. Didn't change after the gas engine ran its first cycle.
     
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    This is somewhat low. It should be around 13.8V. Are you using a decent digital multimeter for your voltage measurements?

    If you should find that the various warning lights come on again, do another voltage measurement when the Prius is READY. Maybe the DC/DC converter is starting to have problems.

    Also check the inverter coolant reservoir for fluid turbulence. If you don't see that, then you know the coolant pump has failed which is causing the DC/DC converter to overheat.
     
  11. Zedhomme

    Zedhomme Member

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    OK. Yes. Have a good digital multimeter. Lights didn't come on, but did another check and wrote it down. 13.9 volts. Will check again if the lights come on. I ordered a Mini VCI which I hope will get here today, so in case of more warning lights I can actually check the codes and maybe HV module output.s. Have an older OBD-II reader that wouldn't give me any readings on the Prius before I disconnected the negative terminal. I had the inverter water pump replaced under the LSC at 78,000. Replaced both the inverter and engine coolant again at about 128,000. Just checked inverter coolant and have good turbulence.
     
  12. Britprius

    Britprius Senior Member

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    Zedhomme, in your first post you said the voltage at the jump point was 12.5 volts, but the voltage at the battery was 12.2 volts.
    Unless you were in ready mode with the battery being charged, "that I doubt because the voltage would be at leased 1.3 volts higher" you cannot have a higher voltage at the jump point than at the battery.
    Basically the further from the battery the more the voltage will drop when not on charge from the DC to DC converter. When on charge from the converter the reverse will apply, the jump point will be at a higher voltage than the battery.

    John (Britprius)
     
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  13. Zedhomme

    Zedhomme Member

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    I'm going to give it another look tomorrow. Not ready to get that involved the day after Christmas, but tomorrow I'll be ready to check everything out again. I have started it up for a few minutes a couple times to check other things and not had any warning lights come back on. I'm inclined to just replace the 12-volt tomorrow and see what happens.
     
  14. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Would not hurt, might help.
     
  15. uart

    uart Senior Member

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    Hi Zedhomme. The problem is that you appear to have run the 12V tests almost immediately after shutting the prius off. This will tend to give false (overly optimistic) readings. I note in particular that your "jump terminal" reading was higher than the actual "battery terminal" reading. As Britprius pointed out, this is not really possible (when measured simultaneously), so I suspect that the battery voltage was rapidly falling and you measured the jump terminal first.

    To properly test your battery you simply need to do it after the car has been sitting overnight. Do it in the morning *before* the prius has been started (or even made ready) at all that day. I suspect you'll then get readings below 11.0 volts in diagnostic mode (acc mode) and even lower in "ignition on" mode (where you hit the power button a second time without the brake pedal). That for example would be a conclusive diagnostic that the 12V battery is gone.

    BTW. Your 13.9V charging voltage is good. So I don't think you need to worry about anything other than the 12v battery itself at this stage. There are some specific conditions where the charging voltage goes down to around 13.4V also, so don't be too alarmed if you also see that happen (particularly during a longer drive). :)
     
  16. Zedhomme

    Zedhomme Member

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    I was out driving it today and still no warning lights coming on, no loss in performance, but on the Energy Monitor Display I'm getting a wider fluctuation of the levels than normal from pegged out green to a couple blue bars. Could the bad 12-volt be causing this too?
     
  17. Britprius

    Britprius Senior Member

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    If the 12 volt battery has a shorted cell this will put a heavy load on the charging system. The charging system is supplied by the HV battery, so this will be discharged more quickly in that situation.

    John (Britprius)
     
  18. uart

    uart Senior Member

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    It could be extra loading on the DC-DC converter or it could just be random and you're looking more for signs of trouble atm.

    Don't worry about other things at this point, just test your 12V battery *properly*. The test is very simple and seems to be extremely reliable at picking dodgy batteries. It just needs to be done correctly, and that means testing the *resting* battery voltages and not those of a battery that is straight off the charger (or same thing, immediately after being driving).
     
  19. Zedhomme

    Zedhomme Member

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    OK. Bad news. I replaced the 12-volt, but after the first drive, the warning lights all came back on. Codes are P0A80 and P3020 Block 10. First question is.
    Since I bought my car in Maryland is the Hybrid battery covered for 150,000 vs. 100,000 miles.
    Anyone know for sure? I have 134,000 miles now.
     
  20. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Look at the warranty/maintenance book provided with your car.
     
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