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Intermittent Electrical Shutdown (lasts 1/2 second)
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08-24-2015, 01:57 PM | #1 |
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Intermittent Electrical Shutdown (lasts 1/2 second)
Hi all,
I have 2006 E90 Sedan, RWD, M6, Build date May 2005. Two winters ago (in Ottawa, Canada, worlds coldest national capital) I noticed an intermittent cutting out of the audio from my stereo, and put it down to a flakey AUX in (factory) or bad cable. Last winter, after driving >10-15 miles, the car would periodically lose all electrical power while driving for about 0.5 seconds. Radio shuts off, instrument panel illumination goes out, xenon headlamps shut off, engine seems to lose power, speedo and tach needles drop, fuel needle moves towards empty. Then the power comes back on, and every warning lamp on the dashboard comes on (ABS, Brakes, DTC, etc), and I can keep driving. Sometimes this will happen every few minutes on longer trips. This summer it has only happened twice - my trips are pretty short and of course the temp is much warmer. After much research, I decided to inspect the fuse box/distribution box/junction box behind the glove box. There is absolutely no corrosion anywhere, positive battery cable looks brand new, nothing to see there! i checked the other end of that cable in the trunk, again it looks perfect. I wanted to check the ground cables in the car - can anyone point me to where I would find those? Any other suggestions on what to look for? Thanks, -speedball |
08-24-2015, 04:32 PM | #2 |
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Did you bring the car in under the battery cable recall two years ago or so? These were the exact symptoms, and what you're describing even sounds like a faulty connector thermal-cycling. You wouldn't have noticed on inspection without specifically looking for this problem.
Secondary question, your car was going completely dead up to "every few minutes on longer trips," and that didn't raise a "fix this right the hell now" flag with you? They initiated a recall because people were having accidents as a result.
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08-24-2015, 07:23 PM | #4 |
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AFAIK The battery recall does not apply to my car. I believe it starts with 2007 MY and up. The reason I checked the fuse box and cable was because of that recall (I figured maybe BMW weaselled out of my year somehow), but my cable shows none of the discoloration or corrosion mentioned in the recall.
If anyone knows of a different recall that covers 2006 E90 I'm all ears. Any ideas on which connector might be to blame? Everything goes out simultaneously, there can only be a few circuits that can cause that. Any ideas on ground wire locations to check? TIA, -Walter |
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08-24-2015, 10:55 PM | #5 |
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It does sound a little like a faulty alternator skipping a beat in the transfer from AC to DC. Might want to just give it a look over, that could explain the intermittent issues you are having.
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08-24-2015, 11:47 PM | #6 |
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08-25-2015, 06:53 AM | #7 |
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Could a faulty / intermittent connection in the battery wire from the BST to the front of the car (goes to boost terminal and starter And alternator) give these symptoms?
Thanks, Walter |
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08-25-2015, 10:30 AM | #8 |
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Have the battery cable checked. Although your car may fail right outside the VIN range of affected vehicles by the recall, it doesn't mean your cable will not develop the same issues. I would start any troubleshooting there.
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08-25-2015, 11:16 AM | #9 |
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As I mentioned in my initial post, I have checked my battery cable for the corrosion and discoloration where it meets the fuse box as recommended by the TSB. Are you suggesting I inspect the entire battery cable from start to finish? I'm game but just saying that's not what they do for the TSB....
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08-25-2015, 12:07 PM | #10 | |
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08-25-2015, 12:31 PM | #11 |
Fuck it dude, let's go bowling.
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Same exact symptoms I was having - battery cable recall did the trick. Have you seen the dealer's recall procedure so you know exactly where to look? Someone once posted it on here.
If it's not that, then yeah I agree that the ground should be checked. Unfortunately I do not know where it is. Motor mount?
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1M. Previously: '13 135is; '07 E90 335i; '02 325i; '99 Z3; '98 328is; '87 L6; '77 320i
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08-25-2015, 12:59 PM | #12 | |
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-Walter |
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08-25-2015, 03:12 PM | #13 |
Fuck it dude, let's go bowling.
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Check out the attached BMW internal memo. The issue is that the connector is coated with tin, which degrades over time and causes intermittent power loss. According to my version of the repair guide (also attached), the discoloration is not a clue whether to proceed with repair, but only to detect excess heat which warrants replacing the fuse panel also.
Not trying to steer you in this direction, just making sure you're positive this isn't the issue. Also, from your version of the repair guide: 4. If no discoloration is found on the cable insulation, proceed with standard troubleshooting to identify the voltage drop in the battery cable circuit. I'd look around for that "standard troubleshooting" guide.
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08-25-2015, 04:41 PM | #14 | |
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Thanks again. -Walter |
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08-26-2015, 10:11 PM | #15 |
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Ok, well I may have eliminated some possibilities and perhaps found the source of my problem. I've attached a few photos here, not sure how to embed them in the post.
1) I found the ground wires in the engine bay - on the passenger side, just near the front right corner of the engine bay, is a hex post that attaches a little plastic "briefcase" with several brown wires entering it. I pried open the briefcase (its sealed at the bottom with some black gooey substance), and everything in there looked good, if a little dusty. I did a quick continuity check from all the internal connection points to the external point where the post connects, and it was all good. 2) I stumbled across another forum post where somebody mentioned corrosion and poor connection where the "positive battery cable" that runs from the BST to the Starter/Alternator exits the battery compartment and runs outside the vehicle. Since I struck out on the fuse box/B+ battery cable I decided to give it a try. I removed the rear power distribution box, the battery, and then set to work disconnecting the "positive battery cable" (big red one) and DME/Valvetronics power cable (little red one that has a snap in connector on the other side that connects to the rear power distribution box). The first sign that I might be on to something was when I removed the smaller positive cable that goes to the DME and Valvetronics - the nut holding it on was corroded and the metal connector had a little corrosion. Then I removed the rear passenger wheel and the rear part of the fender liner, and exposed the external connectors for those two power cables. The "positive battery cable" connector looked ok, but the DME/Valvetronic connector was broken in several places and the inside severely corroded. I'm not sure how to even replace that connector - the only part I can find is this one: 61129125036 , which is the entire 2-wire external wiring harness that runs from the battery compartment to the engine bay - that seems like a painful one to replace. Any suggestions? |
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08-27-2015, 11:59 AM | #16 |
Fuck it dude, let's go bowling.
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Great info - thanks! I saved that battery routing diagram.
Screen grab from realoem: Your last picture - that's from the battery end, correct? On the long cable (the one that routes up to the engine compartment), that special connector appears crimped onto the cable - probably why it's not available as a separate part. That recall procedure doc I posted earlier shows a special tool that BMW uses to crimp a splice connection together. If you found a good cable end (say, from a salvage yard), you could beg them to loan you the tool to crimp a new end on Then heat-shrink on some plastic tubing.
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08-27-2015, 12:54 PM | #17 |
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Those definitely look crusty as hell.
You can probably get away with not replacing anything at all - I'm guessing a quick soak in vinegar and some elbow grease with a scouring pad or steel wool will clean those parts up nicely. If you use steal wool, be sure to wash with water and a sponge after, you don't want to leave steel particulate in there. Oh, and this might seem counterintuitive, but when you put everything back together, maybe give it a spray-down first with WD-40 - it won't really bother the electrical connection much as long as you reassemble everything tightly, but it'll hopefully avoid future corrosion.
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08-27-2015, 02:49 PM | #18 | |
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Going to try the wreckers tonight.... |
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08-27-2015, 03:04 PM | #19 | |
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Anyway, my point is, it's definitely SAFER to completely replace the hardware, but if it truly is a problem of junction corrosion, cleaning the corrosion off should absolutely be sufficient. Even if the surfaces aren't mechanically as ideal as they previously were due to pitting and that sort of thing, they'll be plenty good enough.
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08-28-2015, 01:47 PM | #20 | |
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Anyway, I cleaned up all the contacts and reassembled everything, however before I started the car I checked the voltage at the battery (12.06V) and a few key points around the car. At the positive "jump start" terminal under the hood, I got the same voltage (12.06). When I popped the plastic cover off that covers the connection of the positive wiring harness to the positive cable that runs to the DME (ie the other end of the cable with the corroded connector), I would get variable voltage starting at 8-9V and then eventually rising to 11.9 V. can this be attributed to the DME electronics including some capacitance that is charging up using the multimeter? I plan to measure it with the car running tonight to see if it is any better. I didn't take a picture but there was lots of road gunk on that connection as well - I'm thinking I may take it apart and clean it just in case it is making a poor connection. -W |
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08-28-2015, 02:01 PM | #21 |
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So when you're probing around the car without anything (major) running, you'd expect to see identical voltages even if the junction resistance due to corrosion is huge. It's when there's current flowing that you'd start to see drops.
Which is why it's very odd that you ARE measuring a drop at the DME. There's a definite possibility that you're not using sharp enough probes or pushing hard enough - what you're seeing could happen if your probes are measuring through a very high junction resistance, like they aren't poking well through built up grime and oxidization. That's the main reason good probes are super sharp. But it'd still be weird to see a noticeably slow build-up. And you're right that sometimes you can see weird leakage effects where the device under test gets charged slowly by the tester, but CHARGING is almost unheard of - what you'll much more commonly see is a voltage falling as you bleed charge off a measured capacitor through the 10Mohm resistance of the meter. So what you're seeing on the DME is definitely something I'd consider odd. And if there's some other effect going on, not that I'm convinced that's even corrosion, it could definitely result in the brown-out you're seeing (although I'd be surprised if brownout to the one module resulted in the whole system momentarily shutting off.)
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Last edited by alexwhittemore; 08-28-2015 at 04:03 PM.. |
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08-28-2015, 03:10 PM | #22 |
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I agree - when I scraped the probe a little back and forth the voltage seemed to jump up faster - I'll give that terminal a cleanup and try again with the car off and with the car running. I'm using a Fluke multimeter with your "standard probes" similar to those in the attached photo, not the "needle" type of probe.
Thanks for your help. -W |
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