Got the alternator brushes.

Started going over how to get the alternator out of the car and decided it's a weekend DIY job rather than an evening DIY job

Will return with an update during the weekend. Fingers crossed.

 

@skywampa : Short version: when you have a chance, if you’re up for it, validate our theory that this is a power/voltage regulation problem by putting a constant voltage monitor in play (I have used both BimmerLink and an old school voltmeter with probes connected to a cigarette lighter adapter while driving — same net results both ways, if the regulator is wonking out voltage will be all over the place or too low or both).

Longer version: So in a decidedly strange twist, get this.

I took on the alternator rebuild last night but didn’t get as far as removing it from the car — with the F56S the special tool for releasing tension on the serpentine belt is non-optional. I have a generic tool for the job, but a standard 19mm crows foot will not fit inside the tensioner pulley to grab it well enough to lever the whole thing. I thought I had sufficiently tested the generic tool, but nope, I blew it. So after removing the intake manifold (!) and other bits to get to the alternator — with my last thing done to disconnect the battery cable from the alternator post — I put it all back together again so I could actually drive the car.

While on that driving run — which was several hours — I live-monitored the alternator output (using BimmerLink) and live charging status of the battery. Guess what? For the first time since the shop and I discovered obvious voltage regulator trouble there in early December. For four straight hours of driving the alternator output was pitch-perfect and charging the battery nearly 100% of the time. This remained the case even with a ton of the electrical loads spun up. You would have thought I replaced the regulator. Nope, that was the plan, but I didn’t get that far. 14.x volts almost the entire time regardless. And *really* stable, for the first time I’ve ever seen it: a one-time (early drive) low of 13.98v, a high of 14.71v, and most of the time between 14.22 and 14.51v.

What happened?

Well, one of two things.

(a) I found corrosion on the alternator bolt (like what you see routinely on battery terminals). Not much, to be sure — only on the outermost edge of the nut securing the cable to the bolt. Nothing else. Regardless, I cleaned it up and added a tiny bit of dielectric grease to the nut flange and alternator before reassembly.

Either that made one whopper of a difference or...

(b) because the temps are so low with this cold snap here in the US — battery temperature underhood never got above 40 degrees F while driving — the voltage regulator is suddenly happy due to liking things cold.

My money is on (b) since heat causes permanent-but-failing electrical contact junctions to open as they begin to fail from expand/contract/vibration cycles. But I can’t prove a thing.

So now I’m going to watch how it behaves as the cold snap eases (it was 7 degrees F outside before the sun came up today).

I‘ll replace the regulator and brushes anyway after all my observation-making is done, it'll be a few days, but this was definitely illuminating and unexpected.

 

Well, have an update with some unexpected twists and turns.

(1) The undercharging / heavy voltage fluctuation issue returned quickly. No surprise there.

(2) Figured out that -- in theory at least and with some dexterity -- I could replace the brushes and regulator without completely removing the alternator from the car. Well, got the brushes replaced, but not the regulator. Why? One of the electrical contacts of the regulator is literally clamped onto a corresponding conductor on the rectifier assembly. I have replaced voltage regulators before but encountering this is a first for me personally. The rectifier-side component is small and would be damaged for sure by imprecise work or trying to "wrestle with it." So I settled for replacing the brushes to see what improvements I got, if any.

(3) The voltage regulation problem (and the other fallout it causes) went away again, like the last time, on first drivearound after connecting everything back up. And then on the next day, it came back. I suspect that computer control of the alternator, based on data from the car lost during both major disconnect attempts (I had things disconnected long enough to end up having to reset the clock on the car both times), is in play here. Takeaways: (1) not a huge surprise, (2) demonstrates that the alternator can do its job and maybe at least part of the issue is somewhere else, (3) makes troubleshooting more complicated.

(4) In the "troubleshooting more complicated" list, I am paying more attention to an error citing existence of a short circuit somewhere, which returns at each run of the car even if the errors are cleared -- but does not say where in the car the short is actually supposed to be. Fun. Originally I thought the error citing a short was just part of "the insufficient-power-induced complaint stack." But now I'm firmly thinking it is of independent origin and at least "a" cause of the insufficient power issue. After all, a short circuit may as well be a power siphon -- even if a low-draw one.

Finally, more on the "it's the alternator" side of things -- but I suspect a new alternator would eventually be flummoxed by this mystery short circuit (unless the short is in the existing alternator itself -- doubt it), there is an interesting set of comments under . The video isn't the important part, a BMW owner DIY replaces his alternator and, uh, learns a couple of things while doing so. The relevant comments are:

So @skywampa , the relevant general takeaway for me is that power issues are going to cause all the weird you and I encounter, but the problem remains "what specific thing is causing the power issues, and are there maybe multiple things, and can those multiple things damage/wear out the alternator itself over time just like a dying alternator leads to a worn-out battery?"

I have two identified possible sources for a short circuit -- an AUC sensor that is apparently toast according to error logs, and a ride height sensor wire pair, strapped to the frame and tucked behind the RF fender liner, where the insulation has been compromised and I see bare wire. I have a couple of other loose theories as well, but the bottom line is that if I can't chase it down, it will remain a wildcard screwing up the troubleshoot. The compromised wire is something I can tackle quickly. AUC sensor should arrive maybe next week.

More to come.

 

Ok - final update:

I've pretty much fixed the "electrical weirds" of my F56S. For detail on what was actually the problem, see this thread. It wasn't the alternator, it wasn't the battery, it wasn't the power steering rack, etc., etc., etc. It was indeed a parasitic draw -- from a Genuine BMW/MINI accessory added to the car in 2021, installed following BMW/MINI's provided instructions. Failed battery, charging weirdness, electric power steering (EPS) issues, all of those were side-effects.

I will say that I am glad I changed out the alternator brushes. They were about 1/2 gone. Replacing the regulator/controller (the regulator is DME-controlled) was not possible as a practical matter because it has a contact that is spot-welded to a stator contact. Sure I could get it off and get another on with some effort -- but since things are working, it's not really worth tearing the thing apart.

I may have one or two minor ghosts in the car that I'm only aware of due to being so nosey into the error codes I find in BimmerLink, but beyond that have pretty much got this resolved.