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      10-24-2020, 11:21 PM   #1
Reborn_
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Intermittent power (electric) loss

Any input is appreciated. Out of the blue, my 07 M coupe started experiencing transient electric power loss. When the power loss happens:
1. the abs, e-brake, and traction control lights come on in the instrument cluster.
2. The interior lights for all buttons turn off. The nav/radio turns off.
3. The headlights stay on.
4. The car continues to drive almost fine, but it feels like the engine power is reduced.
This lasts for 1-3 seconds and then back to normal.

The episodes seem to only happen when the car is warmed up. They can happen randomly as one offs or 30 times in a row. Seems to happen more when I have throttle open, but it happens when idling (rolling) as well. It does not seem to happen when Iím stopped. The car starts just fine.

When this first started happening, I chalked it up to the 7 year old battery. I put a new battery in, cleaned the cable terminals (neg was great; mild corrosion on the positive) and I used Vaseline for dielectric grease.

My next step is to clean and check connection of the terminals in the engine compartment for jumpstarts. Would love any other suggestions though!
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      10-25-2020, 11:34 AM   #2
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The alternator/regulator could be going out? How old is your alternator?
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      10-25-2020, 12:50 PM   #3
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It's original. 55k miles. That will be my last resort due to cost/effort. What about the BST?

https://www.zpost.com/forums/showthr...cal+power+loss
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      10-25-2020, 05:58 PM   #4
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BST is a possibility, but I would have guessed that it either work (intact) or not work (blown).

Another possibility is the ignition switch, which is a common problem on BMWs
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      10-26-2020, 02:59 PM   #5
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At that mileage you could just swap the voltage regulator and not replace the entire alternator. I did that around 80K as a proactive measure.

https://www.ebay.com/itm/NEW-VALEO-O...QAAOSwY2pesYA2
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      10-26-2020, 03:53 PM   #6
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Quote:
Originally Posted by XMetal View Post
BST is a possibility, but I would have guessed that it either work (intact) or not work (blown).

Another possibility is the ignition switch, which is a common problem on BMWs

I replaced the ignition switch ~10k miles ago so I think that's fine.

That's my problem with this issue - I agree on the BST, but I would also think if it were alternator related, I would have starting difficulty. So strange.


Quote:
Originally Posted by elerner61 View Post
At that mileage you could just swap the voltage regulator and not replace the entire alternator. I did that around 80K as a proactive measure.

https://www.ebay.com/itm/NEW-VALEO-O...QAAOSwY2pesYA2
Noted, thanks for the suggestion!
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      10-26-2020, 04:15 PM   #7
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Another useful thread:
https://www.zpost.com/forums/showthread.php?t=1021920
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      10-26-2020, 09:18 PM   #8
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Had the same issue this summer.
Scanned the ecu and note a code for ABS over voltage.
Did some research and Swapped the alternator, now trouble free.
I did find an eBay seller that just sold the voltage regulator which would have likely solved it but didnít want to waste too much time on this.
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      10-26-2020, 10:22 PM   #9
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Yea. I figure if I’m removing the alternator, I may as well replace it and the voltage regulator. Still need to check under the hood connections and hook up INPA before I buy parts.
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      10-30-2020, 12:54 PM   #10
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Some quick multi-meter measurements show all is good, but I'm going to go ahead and replace alternator and see how that does - will report back on outcome from there in a month or so.
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      11-21-2020, 11:25 PM   #11
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Installed the new alternator. No symptoms on a drive that had exhibited symptoms twice before (picking up food at a favorite spot), so looks like the voltage regulator was the culprit. I'll keep an eye on it as I get some more miles racked up, but unless I reply back, the issue is solved! Thanks to everyone for the insight - greatly appreciated!
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