12V battery replaced with wrong polarity

[hawkjm73]

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.

[Patrick Wong]

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.

[jayman]

Originally Posted by hawkjm73

Looked at the battery again, and to my horror, the battery polarity was opposite of the OEM battery!

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

[Patrick Wong]

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.

[KK6PD]

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

[efusco]

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.

[tochatihu]

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?

[hawkjm73]

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?

[efusco]

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!!!

[Patrick Wong]

Originally Posted by hawkjm73

...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?

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.