A simple way to continuously monitor the state of charging under the full range of load / driving conditions is to buy one of these on eBay for $2 (probably more if you need it soon) and stick it in the 12V power outlet.

Attachment 77967

Good tool to have even before you have any problems so you can figure out your car's voltage profile before anything goes bad.

Or check the voltage on cluster hidden menu.

The problem with either of those is they won't catch momentary dips or peaks. Not that they won't catch a dip long enough to catch the problem I usually recommend first to use the hidden OBC menu.


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The cluster update rate is not the fastest but if the voltage fluctuations causes various warning lights I would guess that it would show on OBC hidden menu.

if the dip is long enough to make lights come on the dash board you should be able to see it.

Guys, finding a alternator on a BMW 3.0 engine going south is not rocket science. To quote the previous post by Andrew, "use a DMM that has min/max capability or a scanner like Foxwell which has graphical capabilities". Road test and record as you drive over bumps, stop and go, highway, etc.

If the voltage jumps back and forth between charging voltage and battery at rest voltage, you have a problem with a alternator, wiring connections and or grounds.

Take a few seconds, hook up your DVM and check your battery voltage and do a volt drop test on the battery grounds and cables, clean the jumper points under the hood. Set your meter to min/max and go for a drive! SIMPLE

Base line numbers
Battery Voltage should be 12.6+V (Key off) See chart below.
Battery voltage should be 13.5v - 14.5v on running tests (note large fluctuations at running RPMs is a SURE sign that the Volt Regulator is not doing its job. Smack with rubber hammer and retest. Rebuilt units have large variance of quality control from good 85% of the time to approx 50/50%.

NOTE: The exact charging voltage will vary according to the battery's state of charge, the load on the vehicle's electrical system, and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.8 to 14.3 volts at 77 degrees F. But at 20 degrees F. below zero, the charging voltage might be 14.9 to 15.3 volts. On a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts.

Get a new unit that matches you old one Brand and max AMP output.

https://www.ecstuning.com/b-valeo-pa...317501599~val/

Valid on newer vehicles with IBS. On these older ones the charging voltage should be very stable regardless of the situation.

I think all e53 have Irritable bowel syndrome


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I agree. Either that or Colitis ulcerosa, but no Intelligent Battery Sensor.

Coreect not until e70. I've programmed new batteries on other BMW and it's very interesting to read the histogram off of the (other) IBS. It will show how many hours at each state of charge broken down by 20% groups. 0-20,20-40,40-60 etc. It instantly confirmed my clients battery was shot when over the past six months or something the state of charge was mostly under 60 and almost entirely under 80.