hi all,
what kinda problems will be caused by connecting the wrong terminals while trying to give a car a jump.
it's a 2007 mini cooper base, auto.
will the computer get fried or the wire harness?

thanks.

 

Did you connect in the wrong order, or do you mean you did plus to minus.

If you did plus to minus, you will double the battery voltage potentially and create 24v (less if the "dead" battery was just low).

This should blow a fuse or 2, but if it doesnt blow fast enough, melted wires and burned out electronics.

Better question is does your car do anything at this point other than look sad.

 

the car is at the dealer right now, they told me that they think the computer ot the wire harness is gome bad as a result of a bad jump.
the car turns but won't start, battery died, and I did not do a thing to it.
the dealer stating that no communication the computer is being made right now, and they can't find the problem, thier guess is the computer or the wire harness.

 

Not sure what the prices are right now, but if you can find an independent place to swap a computer and try that, I would do that first.

My feeling is the dealer will put a new computer in, that doesn't fix it and then you still have to foot the bill for it, all electronic items are non returnable once installed.

They will keep throwing parts at it till it is fixed, which can get expensive.

Mention where you are located and someone might be willing to help you out with spare part swaps, if it is the wiring harness, that would suck.

Have you tried the sniff test and smell for burnt wires? Also did they say they checked all the fuses? I know lots of cars have a big fuse link for the main battery line.

 

well the wire harness is about $1600, and the computer is $2600.
I'm towing my car back home tomorrow, not going to have the playing a gussing game on my car, I am in Fairfax, Va.
my question is what wire harness are they talking about? where is it located?

 

Could be engine harness or body harness are you still in warranty?? If you are pm me

 

no warranty, sol...lol

 

If it turns over, you don't have a dead battery. A starter motor needs a lot of juice.

 

Not sure which car you have, but go here:
http://www.realoem.com/bmw/showparts...45&hg=12&fg=28

Moderators will probably want to move this thread to the appropriate technical forum since this is general talk.

As you can imagine, the harness will go to multiple hard to reach places. Good news is it is only 303 bux list for an early Gen 1 cooper S.

 

It is time consuming, but I would go to autozone or whatever and get a cheap fuse tester and start finding all the fuses to test in the car.

 

It's not going to be fuses I'm w mini tech there's a bst ( neg batt cable from the battery to ground that could have blown can you tell me exactly what it's doing when the key is on

 

every thing looks normal when the key is on, the fuses are all good, the car sounds normal when cranking, no error codes, and it's not a fuel issue, it is an electrical issue.

 

ouch. I have a feeling this is going to be much more expensive than you think.

 

give me the bad new bud, let me see if it is as bad as the news I got from the mini dealer!

 

The wiring harness may not be a simple little harness. It could very well be the main harness that goes throughout the car - and costs something like 6-8k to replace.

What did the dealership say?

 

and the DME (computer).. do you think it's fried?
a new one is about $1100, and it takes like 7 minutes to install, but the chalange is programing it, not to mention that I might need to change other components, so basicly what I have here now is a big boat anchor.
the thing is if it is repairable, then I am going to get it done, but I hate to start this and not be able to finish it.

 

the dealer said they can't fix it, they wanted to install the wire harness, and try to see if that works $1600 bill, if not then they want try to replace the DME, that's anther $2300, and thats still a guess, so other issues might rise.

 

It's kind of weird that the dealer is just changing out parts to diagnose the problem. Heck, I can do that! You'd think they could test the computer with it out of the car. That would narrow it down to the wiring harness.

What does DME mean anyway?

Damn acronyms!

Just a thought, who was the idiot who jumped your battery backwards, if it was a tow company, maybe their insurance will cover it, heck even a good samaritan probably has insurance.

Dave

 

the dealer claims they can't test the computer also known as the DME or the ECU, they said they can't communicate with it thats why they assume that either the wiring or the computer is bad.
the jump is just a guess, no one knows what happened to cause this problem, so they assumed that the cause MIGHT be a jump was done by hooking the positive on the negative.
all I know that the engine is not getting power (electricity) to the plugs and the computer.

 

BTW: when you connect positive to negative, the live battery tries to reverse the polarity of the dead battery, which results in the dead battery acting as a short circuit (no resistance to the flow of electricity). Depending on how the car is wired and what was turned on during the bad jump, this could also damage other electrical components due to both the high current and the reversed flow of electrons.

The voltage doesn't change, but you get a huge spark when the connection is made, due to the huge amount of current that runs across the short circuit.

To double the voltage of a lead-acid battery, you have to double the number of cells connected in series inside the battery. Each cell provides about 2 volts, which is why non-sealed 6 volt batteries have only 3 caps on top, while 12 volt batteries have 6 caps; one cap for each cell.

 

When you wire 2 12 volt batteries in series you get 24 volts without an increase in amperage. Wire in parallel and you get 12 volts and double the amperage.

This would be a short, not a series connection and no 24 volts.

gary

 

Gary: correct on both points. Voltage is a function of number of cells in series, and capacity is a function of plate area.

One caveat: when connecting two batteries in parallel to get more capacity (amp hours), you have to be sure the batteries have exactly the same voltage. If the batteries aren't voltage matched, the battery with the slightly higher voltage will continually try to charge the lower voltage battery, resulting in a loss of overall battery capacity.

 

Ok, I'm confused.... to OP start from the begining...if you will..

You wrote you didn't do anything to your car...

Was it driving fine one day then just wouldn't start? Did you or a family member try to boost the car? Were you driving and the car just die?

If you/anyone didn't connect another power source to the car that would help a little... "you didn't fry anything"

Now that these cars have all sorts of connectors it may just be a loose connector or corrosion in a connector...

What did you do to your car prior to this happening... any mods? lighting? radio work? off roading/ jumping curbs/ huge pot holes...

Hopefully it's just finding a connection or non connection,(something un plugged) if the ECU/DME can't be found...

 

Royhaddad

To break down what happened The positive terminal of one battery, was connected to the negative of the other battery, in a seperate car. Left alone this will generate some heat, as evidenced by putting two 9 volt batteries together to make a cheap pocket warmer.
In this scenario there is no "normal" return path to chassis ground, as the negative return path was unavailable for either vehicle in this configuration.
However what did happen was that a large positive potential was placed on the chassis ground side of both vehicles with respect to the incorrectly configured battery jumper cables. As the vehicle was attempted to be started this potential increased as positive was now at a chassis ground. In essence the input/output drivers of any electronic devices that are connected during the start sequence were in a sense, "reversed biased". I'm sorry, but all bets are off if this is done.
While some amount of current flowed due to the potential differences. I wouldn't think that you ever got full battery current draw in either vehicle.
This doesn't mean that some wiring didn't get fried, as new cars use the wiring harness and seperate connected loads as current limiters, via fusing and simple Ohms law for DC cicuits. To balance the total current draw.

I would start with the CPU in your position. That's me though. I do find it hard to understand why the CPU can't be removed and tested from the harness seperately.

Good luck.

 

I did that by accident once in the dark, jumpstarting my sister's honda. blew the master fuse in her car. didn't hurt my eclipse any though :D

still, I can't see how the ECU would get cooked without the battery fuse being blown unless the '07+ doesn't have such a 80A (or higher) fuse. a volt/ohm meter would indicate if there's any shorts in the harness leading into the engine computer... on top of that, it sould be idiot proof as well and have diodes on the power leads...
I digress, good luck.