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12V battery replaced with wrong polarity

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by hawkjm73, Jun 4, 2008.

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  1. hawkjm73

    hawkjm73 New Member

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    Well, I just did myself in. After a series of user errors, my Prius is non-functional. My 12V battery had been showing signs of death, and finally failed to boot th car yesterday morning. Hearing of $170 toyota replacements, I checked the auto parts store and found a $80 version at Autozone. (first mistake) Got the battery into the car, but the terminals were too large. I "adjusted" the the connectors until they fit. I then attempted to start the car, but got no response whatsoever. The amber taillights were on, but nothing else. Looked at the battery again, and to my horror, the battery polarity was opposite of the OEM battery! I quickly removed the leads, then turned the battery around to connect it properly. The terminals were originally towards the interior of the car, just like the OEM, now they are toward the exterior, and the vent system can't go back together like that. Definitely not a usable battery. Once I had the leads on the correct terminals, I attempted to start the car again. The led in the power button flashed but nothing else happened.

    I am going into the Toyota parts department today to get a correct battery, new connectors, and whatever other parts I'm going to need. I haven't checked yet, but I suspect the big 100A fuse is dead. Any other suggestions I check out? I'd rather not make multiple trips in, as the dealership is a pretty long trip from my house.
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Jenny,

    Yes, you will need to carefully check every fuse (suggest you remove each one in turn, using long-nose pliers to remove and reinstall), and I suggest you make note of the names of every popped fuse. Note that there is a fuse box under the dashboard near the steering column, as well as the fuses in the relay/fuse box near the inverter. Also check the fuses in the fuse block attached to the positive battery terminal.

    It is likely that the DC to DC converter in the inverter was destroyed, which will be a four-digit repair bill at your dealer. If you can buy a salvage part and can find a hybrid-trained independent mechanic to replace the inverter, that will save quite a bit of money.
  3. jayman

    jayman Senior Member

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    I'm hoping it was just a few blown fuses, but you had better prepare yourself for a very huge repair bill

    The Achilles Heel of the Prius is either jumpstarting with the jumper cables reversed, or hooking up the battery reversed. It can prove fatal to the car
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The OP's situation is the worst of all possible cases, because the new battery was installed backwards. In that scenario, the 12V bus had 12V applied to it with reverse polarity.

    If the problem was reversed jump cables, at least the installed battery would short out the voltage provided by the jump cables, so the voltage on the 12V bus would be negative but substantially lower than 12V (depending upon the internal resistance of the installed battery). And the huge spark created should be good warning that a problem exists.
  5. KK6PD

    KK6PD _ . _ . / _ _ . _

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    WOW, don't we hope Toyota thought of that and placed a steering diode in line with the + side to prevent this from being really bad!!

    If you smelled any burnt electrical smoke kinda smell, well Egon, Thats BAAAAD!

    On the other hand, if you did not notice any smell, well keep yer fingers crossed!!!

    I repair electronics every day, well excluding weekends unless I am on overtime, I have seen the results of backwards power. Made me a lots of money fixing the results!!

    Please post a follow up, I would like to hear a Positive ending to this!!

    A little electrical humor there hehe!!

    Good Luck
    73 de Pat KK6PD
  6. efusco

    efusco Troll Slayer Staff Member

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    My money will be on a blown fuse, doubt there was ever enough juice to get to the DC-DC inverter to do any damage. Does sound like saving $90 is going to cost you a bunch tho.
  7. tochatihu

    tochatihu Senior Member

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    Pat you are right and it has been said before. Because Prius never takes big amps from the 12 v battery (normal ops), there is a golden opportunity to polarity protect the car. At the same time Prius has more than average # of ECUs and the worst case scenario here would be hard to out-do.

    Toyota, please while you are working on the Lithium suitcase and the aggressive youthful trendy hood design, how about some polarity protection?
  8. hawkjm73

    hawkjm73 New Member

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    Two trips to Toyota are going to be required at least. The 100A fuse is blown, and nobody in my area stocks it. They should have it in today, though. So, my first damage found was the 100A and two smaller fuses. I did check them ALL, hood, steering wheel, and over the battery.

    Surprisingly, when I did the major no-no connection, nothing obvious happened. There were no sparks, no smoke, no smell, no pops, no clicks, no groans. It just sat there. Don't know if that means anything, but I'm trying to be cautiously optimistic.

    I won't know more till later today, as without the big fuse, I'm just cooling my heels. I'll definitely let you all know the result. When I get the correct battery in and the fuses swapped, if the car starts and doesn't complain, will that mean I am in the clear? Will there be an obvious symptom if the inverter is blown?
  9. efusco

    efusco Troll Slayer Staff Member

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    If it starts and runs without any major DTC codes/CELs I think you're in the clear and can kiss that blown 100A fuse for saving your butt!!!
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Jenny,

    Thanks for the update. What are the names of the two smaller fuses that popped?

    I am surprised that you saw no spark upon connecting the battery. If enough current flowed to pop a 100A fuse, there should have been a very big spark.

    If the car becomes READY, then you are good to go.

    If the inverter is blown, then the car will not become READY and you will see warning lights appear (probably the red triangle master warning light, the hybrid vehicle icon in the MFD, and maybe the check engine light in the combination meter assembly). Unfortunately, I believe that this scenario is the more likely of the two.

    The various ECUs are diode-protected against this reverse-polarity problem. However the DC to DC converter is not. This is probably because 1) lots of current potentially can flow through that system and 2) a silicon diode introduces 0.7V drop. That drop combined with potentially 100A of current flow results in a pretty big power loss.

    EDIT: Actually, the way to protect the DC to DC converter without introducing a power loss would be to connect a diode rated at >100A current to the 12V input to the DC to DC converter, cathode to that input and anode to ground. The diode would do nothing under normal use. In the event that negative voltage was applied to the 12V bus, then the diode would conduct and allow the DC/DC 100A fuse to pop.
  11. hawkjm73

    hawkjm73 New Member

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    Thanks. I was confused about the fuse as well. I seems something ought to have happened, not just quiet nothing...
    My repair manual files are AWOL at the moment. Is there a set of instructions anywhere to get the 100A fuse out? It's a 2005 model.





    You better believe I will!!!
  12. pjm877

    pjm877 Member

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    I too got an "American" 12V Car Battery, but I got a Japanese to American conversion Kit from someone on the internet to convert my 2004 Prius to use a 2004 Mazda Maita battery. Only had slight problems using this battery, but this battery is 2x times better than the Toyota Japanese battery.

    The cost of the battery was under $90, and not the $250 quoted from my local Toyota parts dept.

    But, when I got home for the first time with this Mazda battery I saw that to install correctly the "+" and "-" the battery had to be turned 90 deg, and that would put the connections out of reach of the Prius connectors. The reason for the search for the KIT.

    Lets hope that the American Battery Mfg. see the light and start making a battery for our 2001-2003 and 2004-2008 Prii. When and if they do... I might change out :)

    later
  13. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Jenny,

    I assume that you are talking about the 100A DC/DC fuse. Is it your understanding that the little fuse link can be replaced individually; or must the entire 5" long grey/clear plastic assembly that contains all of the fuse links be replaced?

    If the entire assembly must be replaced, then it looks to me that removal will entail removing the nut on the dedicated jumpstart terminal and removing another nut on the side of the assembly. Then it can probably be pried out of the relay/fuse box. My repair manual is silent on this question.

    What are the names of the other two fuses that had popped?


    Hi Perry,

    The Mazda Miata battery works better with Classic, since the battery terminal polarity is correct for that car (the Classic battery is located in the left rear fender.) When the Miata battery is used with 2G, it is necessary to install the battery so that the terminals are next to the fender. If that fender is hit in an accident, then you have a greater risk of creating a big electric spark.
  14. hawkjm73

    hawkjm73 New Member

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    After quite a bit of time searching the part guys computer, it appears the fuse is an all or nothing repair. I ordered the whole grey/clear plastic box with all the fusible links. (@60 dollars by the way) I do see those two nuts, and I think they should let the assembly release. Sounds better the the adventure involved for the <2003 models.

    Sorry, I saw the question about the other fuses earlier, but I forgot to go fetch the page I'd written them on. They are:

    ETCS and Dome

    Both in the left column of the under-hood fuse box.
  15. KayakerNC

    KayakerNC Member

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    :fish2:


    Jenny,
    We're all rooting for you.
  16. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Thanks, Jenny. Are you planning to try to remove the old fuse link assembly now? (In case something breaks, you can call your friendly parts guy and order a new relay/fuse box, thus saving another trip to the dealer!) :rolleyes:

    Thanks also for the info on the other two fuses. The DOME fuse provides power to keep the combination meter memory powered up at all times. The ETCS is for the electronic throttle control and provides power to the engine ECM. Not sure why those fuses would have popped if the ECUs were protected by diodes. I guess you will find out soon enough if there's any damage there.
  17. edthefox5

    edthefox5 Senior Member

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    EDIT: Actually, the way to protect the DC to DC converter without introducing a power loss would be to connect a diode rated at >100A current to the 12V input to the DC to DC converter, cathode to that input and anode to ground. The diode would do nothing under normal use. In the event that negative voltage was applied to the 12V bus, then the diode would conduct and allow the DC/DC 100A fuse to pop.[/quote]


    Uh..no. You don't want anything to conduct. Proper reverse voltage protection is usually done with the diode connected in series on the negative side cathode connected to negative terminal. Proper forward bias conduction with proper polarity. No conduction reversed.
  18. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Ed,

    Your statement would be true if you have a circuit that draws relatively little power under normal operating conditions, such as an ECU. In that case, the 0.7V drop of the series silicon diode is of minimal importance as long as you account for that voltage drop when designing the circuit receiving the power.

    With a high power device like the DC to DC converter which is fuse protected at 100A, if you have a silicon diode in series then you will have the 0.7V drop of the diode to contend with. At 100A current flow, this is a power loss of 70W.

    My suggested protection uses the diode as a "crowbar" which will force an electrical short upon polarity reversal, and blow the 100A DC/DC fusible link before the inverter can be destroyed. From the manufacturer's point of view, the blown fusible link can serve as a "tell-tale" that is evidence of a screwed up jump start, while the diode prevents serious damage to the inverter.
  19. hawkjm73

    hawkjm73 New Member

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    For anyone waiting for an update, I apologize for not doing so last night. That fuse is one of the most argumentative, ill-layed out, no-clearance piece of car that I have ever had to work with. I was VERY tired when I got done.

    Apparently, I am one very lucky girl. Once I got the fuse replaced, and everything hooked back up, the car started to ready mode with no codes thrown. I let it run awhile then did a few restarts to be sure. All is good. The 12V system is reading @13.6V while the car is on and @12.3V in the first-press not-on state. My theory is the Autozone battery didn't have much charge and slowly blew the 100A, but didn't have the ommph to damage anything else. I'm certainly not going to test it out, though.

    As for the 100A fuse, I implore everybody to triple and quadruple check electrical connections if for no other reason then to avoid having to change this sucker out. (Although the DC/DC inverter is a pretty compeling reason, too.) In addition to the nut to the jump-start terminal and the nut on the lower left side, there are two bolts on the right side and one on the left deep inside the fuse box. They attach cables to the fuse assembly. Those cables have very little play. There are plastic clips on either side of the assembly, and connecting it to the fuse holder just below it. That fuse holder has to slide up from the 100A assembly to get it to disconnect. There are two multi-wire connectors on the back of the 100A assembly as well. Getting it out was a matter of getting wrenches into nearly impossibly small spaces, and getting it back together was worse. It was horribly difficult to get a hold of the wires well enough to line them up and get the bolts in. The bolts are short and just about any pliers made to much space between cable and fuse to get the bolt to catch. DH had a pair of surgical clamps for model ship work. Those were my best bet here. My mother, husband, and I spent about four hours on this project yesterday, about 15 minuets of which was installing the new, correct battery.
    Cristino likes this.
  20. GatorJZ

    GatorJZ New Member

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    Glad that worked out for you. You must have dome a good Karma thing in the past.
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