Battery Installed Backwards, No More Starting

[beskhu3epnm]

Yesterday me and my brother were uninstalling the alternator in preperation to be changed. I noticed my window was down a little, and rain was in the forecast. I asked my brother to hook up the battery quickly while I roll up the window. Once he was ready, strange things were happening. The signal lights were activated, the check control light in the center of the cluster, among other things were powered up. I turned the key in the ignition on and attempted to roll up the window, no dice. The rear windows started rolling down. I figured it was perhaps an incomplete circuit as the alternator was out of the car.

I re-hooked the alternator connections and had him try it again. Same thing.

I went back to take a look, and he had the polarity of the battery wrong, trying to hook up the negative to the positive and vice versa. Swapped it around, charged the battery and rolled up the windows, thinking nothing else of it.

Received my alternator today, and installed it (brother nowhere to be found - real work). I had the valve cover off to troubleshoot a seperate problem (ignition harness/coils out as well). Install everything as specified and try to start the car.

Nothing doing, won't fire. The starter acts erratically, as the engine seems to only be catching every third rotation or so. It's not freewheeling, but it doesn't seem to be turning it fast enough for some reason.

I've done some searching, and got different answers from different places. Some threads it ended up being the DME, some (E30) were a fusible link, and others the battery simply died immediately.

There is power to the front of the car (front terminal), so I don't think any ground straps are off (these would have been energized by the reverse polarity.

Fuses are okay, although the radio and front window fuses were blown. They have since been changed.

I have a shark injector, and my question is this:

In order to test the DME, is it possible to hook up the shark injector and attempt to remove the program on there in order to generate an error message that it can't communicate with the DME? This would confirm whether or not the DME is toast, would it not?

I have yet to test for spark or fuel. Relays could be the culprit. Is there a fusible link in the system somewhere?

Anyone else have something like this happen?

Drop me a line, lets figure this out. I'm not interested in smart remarks regarding the stupidity of it all, I'm well aware of that already. What's done is done, and my brother will certainly pay the price.

[beskhu3epnm]

UPDATE:

No fuel in the fuel lines. This means the injectors fired, but the pump is not working.

There is also no spark. Perhaps this is EWS related? One way to find out is to use the shark injector... More on this later.

[MURPHY660]

do e36's have like a main power fuse or anything like that? could have fired the ecm. battery probably fried too.

[beskhu3epnm]

Apparently this is going to be my own thread (therapy). (sorry Murphy660, didn't see your post for some reason? Timing? I don't know of any main fuse, though...)

Another update, I used the shark injector to try to communicate with the DME. I got code 132 (ECU not responding).

Next is to test for power at the main harness, I suppose.

Does anyone know off hand where the relays/fuses for the DME are? I've never taken the DME out as of yet (I know, four screws, slides out with some force) but I figure I can test down the line to see what gives.

My radio doesn't work either, but it's getting power from somewhere as I was able to eject my CD (aftermarket Rockford RFX9020).

[benemorius]

Start by charging up the battery overnight and make sure it holds a charge in the morning. Unfortunately (at least in this case) bmw uses a lot more control modules than many simpler vehicles, and those modules are very sensitive to reverse current. I can't tell you which fuses the dme uses off the top of my head, but you need to check all fuses anyway. Check every last one and write down any fuses which are blown, then connect your charged up battery and start replacing the blown fuses. Check whether they blow as soon as you insert them. You might get lucky and find that everything works once the fuses are replaced, but it's more likely that some circuits are fried. If luck doesn't pull through, go back and check the blown fuses that you wrote down. Any fuse that is blown again suggests a high probability that a control module connected to it is fried. You should know that it is not unlikely that the dme itself may be gone. Also, just because a fuse does not blow again does not mean that everything connected to it is not fried.

I do not recommend that you start swapping modules at this point. If you have a spare dme or whatever, save it until you have a better idea of what damage has been done. Simply plugging it in to the harness could zap it if there are still other issues.

Do you have any idea of what the total time was that the battery was connected backwards may be? The longer it was in, the greater the chance that harness wires started melting and shorting together.

Sorry to hear of your misfortune. I'm crossing my fingers for you.

[benemorius]

Also, relays do not typically take any damage from reverse polarity. However, if they contain an internal diode, that may blow. If that happens, the diode may either be blown closed or open. If it is closed, then you will know it because its fuse will keep blowing when you replace it. If its open, it will still function normally but may pose a risk to the module that controls it.

Now having said all that, I don't actually know whether bmw uses relays with internal diodes or not. You asked about relays, and that's what I know about them.

[m2pc]

If the Shark Injector cannot communicate with the ECU, then it's most likely fried. Did you notice any smoke or anything coming from anyplace when the battery was connected wrong?

[beskhu3epnm]

Thanks all for the replies, I do have some more information:

The battery was charged yesterday. It drained quite a bit from the event.

The battery was reversed for about 1 minute or so. I checked my Bentley manual, and offer this information to you:

Fuse 14 - Front Window Lift, Engine Control Module (30A).

This is the fuse that blew (as well as the one for the radio).

I think what happened is that when I tried raise the window, the power from the battery came through the chassis, the DME, the fuse and the window motor last.

This would have exposed the DME to raw unmetered voltage in reverse polarity. If I hadn't of touched that window switch...

Everything else on the car works fine, except for the radio. The fuse blew on the radio, which means that power from the chassis went through the radio unmetered as well, knocking it out. The radio will not operate, however the CD will eject, meaning there is power to the unit.

There is a chance that it may be the wiring? This is something I have yet to test for. The fuses are not blowing upon operation of any equipment (including the power windows), indicating there is no short in the system currently. I would think the wiring would be safe, yet the DME took the brunt of the force (the window motor could handle the step down after the DME cooked).

Am I on the right track with this? All other systems appear operational...

[MRPOWER]

a while back a friend of mine did that while we were working on his RX7 and it fried the ecu after blowing he main fuse, so its deff a possiblity that ur dme is gone, hopefully not though

[beskhu3epnm]

Minor good news, all other basic modules on the car are working:

Sunroof/Windows/Central Locking
ABS/TCS
All chassis and interior lighting
Instrument Panel
Wipers

Only the radio and DME appear to have been affected. And not even the wiring at that.

What about testing relays? Is the DME relay the same as other relays in the system (without obviously checking - it's -5C here (23F)). Can I swap it with something as just a quick check? I will likely test the harness to verify the system is getting power.

Still open to comments and thoughts regarding this.

[fuggle]

In general, components like wiring, relays and motors will not fail under these circumstances. Especially when fuses are in the path.

The parts that won't like reversed voltage are integrated circuits like the radio and DME.

Bentley has a procedure for testing the main relay. I can't tell if the main relay is similar to any of the other relays. You could check the numbers on it to see if they are the same as any other.

The main relay is #2 which is just outside the front power distribution box. There should be 3 together, labeled 1 2 3 from left to right.

Kent

[benemorius]

I believe at least the high and low beam headlight relays are the same. Looking at the entire set of 15 relays (you have to remove the cover on the extra box next to the fuse box to see the first three) while standing at the left side fender and facing the fuse box from the side, they are numbered as you would expect - left to right / top to bottom. Number 2 is the dme relay, and 5 & 6 are the headlight relays you can try. Cross your fingers, but don't hold your breath.

Are you so sure that the radio is toast? Keep in mind - it draws power from two sources. One source is the constant wire. This is what allows it to keep settings while powered off, as well as operate the cd changer eject. The switched source is what it uses to turn on. Ergo, a blown fuse could still be what is keeping it from turning on even if you can eject the cd changer.

I do recommend that you check each and every fuse. You never know what has been blown. It can be very random when reverse polarity strikes.

edit: If you'll give me a minute, I'll look up which pins you need to check for voltage in order to verify that the dme is in fact receiving power.

[beskhu3epnm]

benemorius,

Thank you for your patience and assistance with this thread. The information has been very useful, to say the least (as with the other posters as well). You can post the pin numbers in a new post, I got my eye on this thread for another hour or two yet.

The constant power must be still alive, as I ejected a CD from the unit. Therefore the unit is still receiving power. The remainder of the unit is inoperable, not even able to turn on. I will have to identify and test the wires independently, as the fuse is alive and well. This fuse did originally fail when the reverse polarity made it's way through the system. I removed and carefully checked each and every fuse on the panel, as well as replaced some of the ones that looked a little older.

I will attempt a relay swap first, and if no dice, will remove the DME to test further (the pins of the harness). If the unit is dead, I may try to disassemble to see if perhaps something could be soldered into place, as I'm sure every part of the unit didn't get fried all at once. The pain and suffering associated with transporting my car 400 miles to get the EWS aligned with a new (used) DME is a little overwhelming. I would have to exhaust all other measures first.

If the relay works, I'm in business, but I just don't think the problem would have ended at the relay. It never seems to work that way...

[Praylood93]

i don't know about the e36, but my old e30 had a fusible link inside the battery cable. i had the same problem and it turned out to be this fuse. i had to cut open the battery cable in the trunk and i found two cables, a little one and a big one. the little one had a flat fusible link in it, it was flat, i didn't know it was there (believe me, i felt around) until someone told me. i cut out the blown fuse and installed a 50 amp spade fuse from a stereo install kit. i did check and that link is a 50 amp. hope this helps

[benemorius]

First, triple check fuses 16, 28, and 39. The fsm lists these as the fuses for the dme.

Use this as a definitive last resort before trying a replacement dme.

Once you disconnect the dme connector, look very closely at the inside face of it. You should see numbers at each end of the rows of pins designating the number for the pin at the end of each respective row.

Pin 26 (red) should be hot at all times. It claims to be unfused, but I am somewhat doubtful of that. If you have no power on this pin, either you have a wiring issue or there is an unknown blown fuse which the wiring diagram does not show.

Pin 49 (green) should be hot with the key in the run (second) position. This connection should not be fused. As before, a wiring issue is the likely cause if you do not find power here with the key on.

According to the wiring diagram, it is up to the dme to turn itself on when the key is turned on. Meaning, those are the only two wires which should supply power to the dme harness while it is disconnected.

Plug the dme back in now and move to the fuse box.

Pull the dme relay (#2) taking note of its orientation. Look closely at the underside of the relay. You should find that each pin is numbered. Locate pin #85 and then determine its corresponding socket in the fuse box. With the key in the run (second) position, this pin should be grounded. If you do have a ground here, skip the next paragraph. Otherwise continue on.

Leave the relay disconnected and move back to the dme. You will need to disassemble the harness connector itself in order to backprobe one of the pins. That is to say, you need to be able to check one of the pins while the connector is plugged in to the dme. Taking the connector apart is pretty straightforward. I'll leave that to you. The pin you need to backprobe is #73 (brown). This is the wire which leads to the relay pin you just tested. You are checking it for a ground signal to be 100% sure that the lack of ground is due to the dme and not a break in the wire leading to the fuse box. (unlikely, but 99.9% sure is not the same as 100%) As before, turn the key to the run position and check for ground. If you do not have a ground here you can, unfortunately, be 100% certain that your dme has kicked the can. When you turn the key on, this pin is how the dme signals that it wishes for the main (dme) relay to turn on itself, the fuel pump, injectors, and a few other things. Naturally, if it can't even manage to ask to be turned on... it has just completely quit working.

If you do get a ground on that pin, then your dme is at least functional enough to attempt to power on. How significant that is depends on the inner workings of the dme itself. In other words, I don't know. To test whether the dme is receiving power from the relay when it turns on, you will again need to backprobe as the relay will not turn on without the dme being plugged in. With the key in the run (second) position, you should see 12v on pins 54 and 87 (both red/white) on the dme harness. If you don't, you have an issue with the dme relay or the wiring for it.

If everything checks out up to this point, you at least know that the dme is receiving full power. If it still doesn't work, it may be worth trying to get a known good dme to test with. If you don't have that option, it is possible to further test the dme to ensure that it is bad before dropping the cash on a new one. However, testing gets pretty hairy from this point on. And if you ask me, this has been a pretty lengthy post even as it is.

[benemorius]

According to the wiring diagram, there is a main fuse link at the battery which fuses the only two cables on it. I've seen some models which have a fuse on only the wire which goes to management modules and leave the rest on the wire without a fuse, but this does not appear to be one of them. What that means essentially is that it is probably worth looking, but the wiring diagram for that vehicle suggests that you won't find a blown fuse link there.

If you do wish to look, just follow the positive cable off the battery until you find it. Common sense says that there shouldn't be more than a couple of feet between the battery and the fuse.

[beskhu3epnm]

WOW!

I don't know what to say about everything. Thank you so much for getting that information for me. Owning this car for 4 years and having never been to the dealer, I know a thing or two about DIY projects, and maintenance etc.

This was a new can of worms for me, and something I would have just thrown parts at until it was fixed.

This is definitely within my scope to test this, and I will definitely undertake this first thing in the morning. It seems like a really complex system, and I'd be afraid that my results would be right for some wires, and wrong for others, leading me to believe a mixture of wiring and DME failure.

I can confirm the fuses are OK, I just went and checked those fuses again, and ran the ignition, etc.

I do find it strange that the fuel injectors emptied out the fuel rail, though. No more pressure, where there would ordinarily be. I was certain this action was controlled by the DME.

But the tests will tell though, right?

I will definetely post here tomorrow on this, hope you're around!

Thanks again, and take care

besk

[Lynx]

This is all over my head however I noticed you said you had an aftermarket stereo. Alot of the time these units will usualy have a fuse directly on the unit, have you checked this one? As minor as this issue is for you now maybe its an easy fix as well.

[beskhu3epnm]

I JUST JUST thought of that, too... Your timing is perfect!

I don't remember seeing one, though. There may be something internal as well, if it's not external.

It would be nice... I will definitely report that finding as well tomorrow.

Thanks for stopping by (Canada FTW)!!

[benemorius]

The fuel rail could be empty for a number of reasons. First and foremost, the dme is what energizes the fuel pump. If the pump hasn't run for a while, the rail will have had time to depressurize. It is also possible that the dme may be unintentionally holding the injectors open. Integrated circuits can fail in interesting ways when you zap them with current in unintended ways and it is not extraordinary to think that the dme's injector outputs could be shorted to ground. All in all, I wouldn't place too much significance in the lack of fuel pressure.

[karlow]

FYI electronics are not very forgiving when it comes to being powered reversed. The fuses in the system is to prevent a fire not save the electronics. Relays don't care but them may have a free wheeling diode. The diode would care and short out the battery, if the battery were installed reversed (you should be so lucky). Yes those little diodes would give their lives trying to save your Ass. Most likely you are not lucky and have damaged or blown every piece of electronics in the fing car! It's amassing how a little thing can really plant it deep and break it off!
PS, an after market radio is likely to have some sore of protection from this sort of stupidity. On the other hand it spits our CD's and nothing less it's so likely SOL.
Yes you really Fc%4ed the goose on this one. Try getting another main computer module for starters. I'm surprised anything is working.

Good luck, you need it.

[beskhu3epnm]

FYI electronics are not very forgiving when it comes to being powered reversed. The fuses in the system is to prevent a fire not save the electronics. Relays don't care but them may have a free wheeling diode. The diode would care and short out the battery, if the battery were installed reversed (you should be so lucky). Yes those little diodes would give their lives trying to save your Ass. Most likely you are not lucky and have damaged or blown every piece of electronics in the fing car! It's amassing how a little thing can really plant it deep and break it off!
PS, an after market radio is likely to have some sore of protection from this sort of stupidity. On the other hand it spits our CD's and nothing less it's so likely SOL.
Yes you really Fc%4ed the goose on this one. Try getting another main computer module for starters. I'm surprised anything is working.

Good luck, you need it.

I hear ya man, I hear ya!

All other systems are operational except the DME and the radio. I don't think I'll be so lucky to have a relay quit in time...

If you think about how the power went through the car, it had to go through the chassis and through the grounds as it was reversed. Unless the DME is grounded on the other side of a relay, it was hit early on when I hit the switch for the windows.

Since the windows/DME/radio were the only things activated enough to get a full charge from the battery (blowing the fuse on the other end of the windows), they may be the only things in the system to be affected so heavily. Everything else seems to be ok.

I'll definitely know more tomorrow. The only fuse to blow from the DME (The DME has multiple fuses) is the fuse that's attached to the front window lift (power windows). At 30A, it took some heat. Considering where the fuse is in the system, it was irrelevant.

[MRDWILLIAMS]

I came to speak on it from experience this happen to me 2 weeks ago and i checked everything going from from my starter to my altenator, fuses everything that u can think of. Go switch the fuses that that u blew and replace your dme I promise you that will fire right up!!!!!!

[MRDWILLIAMS]

I completly killed three batteries in the process

[beskhu3epnm]

All signs pointing towards the DME...

Unfortunately EWS is going to get in the way of it firing right up...

Also, living 400 miles from the nearest dealer sounds like working through this is going to be boatloads of fun.

Heading out to pull the unit and test it right now...