random battery drain/ wont start - United Bimmer Community

**gemnilvr** · 10-20-2009, 10:12 PM

hello, i have been having probs with my battery randomly being drained and not turning over, eventually leading to not even making a clicking noise, just completely dead. i can drive the car all day while running errands and then all of a sudden it will be dead. it will always start with a jump and then be fine for a week or so and then happen again, sometimes a month could go by before it happens again! twice now after its been jumped and started, the outside temp reads at -40 or -30 then as i drive the temp slowly reaches the correct outside temp! i have done many diy projects to rectify the prob but it always seems to come back! my service engine soon light is now on and the codes are reading misfire and a few others so idk! i have replaced the blower motor unit and rewired the wiring harness in the trunk but noticed they are getting caught in the trunk again when it closes so it may be shorting out the battery! does anyone know if the faulty wiring can cause the battery to suddenly be dead on a random. or if something else could be causing this! any input would be helpful , it is going to the shop on monday for an oil change and tune up so maybe i will find out then! i will keep my findings posted asap! thanks!

Big Evil · 10-22-2009, 04:03 PM

You have an intermittent parasitic draw....lucky you. Unfortunately that can be one of the biggest pains in the asses to find because its intermittent, and because you have to wait an hour for all the modules to go to sleep in many cases. Usually that kind of issue requires a specific test with some BMW factory tools (GT1 or DIS). I'd suspect the wiring in the trunk, and did you bypass the neg battery terminal on any of your rewiring? The terminal should contain the IBS monitor and bypassing it can cause all kinds of annoying stuff.

**gemnilvr** · 10-22-2009, 04:40 PM

well, im not sure about that, it was rewired at the dealership about two years ago and they just spliced wires together where they were damaged and didnt replace the whole harness so i just tried to twist the wires back together and retaped them with elec tape. so i havent looked yet but maybe they came loose again idk! the trunk is still working but the other wires may be causing probs! so u think they could be causing the battery to short out and drain? if so how does this happen, sometimes its completly dead after a couple tries and then sometimes it just clicks and nothing, i did notice tho when it is flat dead and then jump started( which it always jump starts) the temp display reads like -40 and then as i drive it slowly climbs back to the correct temp, very strange to me! the battery is only 2 years old. i also cant use the alarm because it goes off so frequently that it too drains my battery! so i cant even lock my car up! thanks for responding!

Big Evil · 10-22-2009, 04:56 PM

Hence the horrendous pain in the rear gears.

It's an intermittent kind of thing, which means the test has to be running on one of those rare occasions when its happening or the problem may never be found.

Could be a signal wire from the trunk switch grounding out and triggering the trunk light and waking up all the modules. Could be the stupid neighbor kid with 3 million watt hearing loss machine setting off the vibration detector and waking up modules. Could just be when the wind blows right the the cars sways ever so slightly and a connection gets made inside the harness.

It'll most likely not be cheap, but I'd go back to the dealer and see if they can work something out for you since they did the repair that now seems to be coming undone.

BTW the thread starter is in the blue header at the top of the list

**gemnilvr** · 10-22-2009, 05:14 PM

lol, thanks, i found the thread starter! i did go to the dealer and they said it would be $500 to replace with a new wiring harness but then im afraid the same thing will happen since its just replacing with a new one! im not sure about the other possibilities u refer to but it could be that something is coming on in the night but i never notice that and that wouldnt explain why it sometimes just happens when i get into my car from the store and it could be dead, then i jumpstart it and it could be fine for a week or two and not happen the whole time! i guess is what im wondering is if something can cause it to just suddenly be dead and not start then be fine after it is jumped! i dont recall but my mom said she seems to think that it happens after i have washed my car or had the doors opened for too long, i think it may be when i open and shut the trunk so im trying to not mess with the trunk and see what happens!! it is going to the shop on monday for an oil change and tune up so maybe he can figure something out! i will post to let everyone know so it may help someone else! thanks!