[Slammed911]

Hello, please have a look a voltage dropping when engine reving down to idle, i'm thinking that i need new voltage regulator, am i right ? Thx in advance

[e91Owner]

That's likely it, but better to diagnose it with freeze frame data and pulling codes.

[Slammed911]

I'm getting electric coolant pump power-reduced operation, DME power management and coolant pump missing codes, no CEL, i think these codes are related to these voltage changes. May i order new voltage regulator? Can someone confirm that these voltage drops are not normal?

Coolant pump is OK i think because i never had issues with overheating, no leaks, coolant temp always stays between 107-108C usually and around 90-95C WOT

[e91Owner]

Originally Posted by Slammed911

I'm getting electric coolant pump power-reduced operation, DME power management and coolant pump missing codes, no CEL, i think these codes are related to these voltage changes. May i order new voltage regulator? Can someone confirm that these voltage drops are not normal?

Coolant pump is OK i think because i never had issues with overheating, no leaks, coolant temp always stays between 107-108C usually and around 90-95C WOT

Yes, that is not normal.

[cliffschum]

Shouldn't the vehicle display a definitive code (on the diagnostic) if alternator and/or voltage regulator is weak/bad ?

[e91Owner]

Originally Posted by cliffschum

Shouldn't the vehicle display a definitive code (on the diagnostic) if alternator and/or voltage regulator is weak/bad ?

No, not directly. It will be other electric components that give you the thought to look.

In your case from your other post, I would suspect that may be a problem for you as well. It's super easy to check from the hidden menu or with a volt meter while the engine is running, so might as well rule it out.

And if it is bad, it's $40 and an easy fix.

[cliffschum]

Thanks for reply. My Bavarian Tec diagnostic provides ~ dozen voltages, but no ripple voltage data. Many voltages are over 14V. Advance Auto reading of 12.3V is reasonable for 4 year old AGM battery, indicates 70% charge. Trying to determine if there really is a bad diode in alternator and/or regulator.

[e91Owner]

Originally Posted by cliffschum

Thanks for reply. My Bavarian Tec diagnostic provides ~ dozen voltages, but no ripple voltage data. Many voltages are over 14V. Advance Auto reading of 12.3V is reasonable for 4 year old AGM battery, indicates 70% charge. Trying to determine if there really is a bad diode in alternator and/or regulator.

I don't know how to say it any simpler. You need to check the fluctuation of the alternator output voltage while the car is running. How you do that (scan tool, multimeter, or hidden menu), is up to you.

Maybe watch the OP's video.

[cliffschum]

In my other post, which you read/referenced, Advance Auto already ran the simple test you suggest - unloaded and loaded charging output. They rev the engine, with diagnostic clamped on battery terminals. Voltage only dropped from 14.11V to 14.04…both mid range "green", indicating normal alternator charging output.

Advanced Auto Diagnostic also conducted an additional ripple voltage test, where I'm ~ 10x high, and conclude that I have a shorted diode. Alternators have 6 diodes, voltage regulators typically have several Zener diodes..

"If only one or two diodes have failed, the alternator may still produce enough current to meet the vehicle's electrical needs, but it may not be enough to keep up with higher loads or keep the battery fully charged. This could cause the battery to run down over time."

My battery is at 12.3V, or 60-70%…not unreasonable for being almost 4 years old…

[e91Owner]

Originally Posted by cliffschum

In my other post, which you read/referenced, Advance Auto already ran the simple test you suggest - unloaded and loaded charging output. They rev the engine, with diagnostic clamped on battery terminals. Voltage only dropped from 14.11V to 14.04…both mid range "green", indicating normal alternator charging output.

Advanced Auto Diagnostic also conducted an additional ripple voltage test, where I'm ~ 10x high, and conclude that I have a shorted diode. Alternators have 6 diodes, voltage regulators typically have several Zener diodes..

"If only one or two diodes have failed, the alternator may still produce enough current to meet the vehicle's electrical needs, but it may not be enough to keep up with higher loads or keep the battery fully charged. This could cause the battery to run down over time."

My battery is at 12.3V, or 60-70%…not unreasonable for being almost 4 years old…

I would say your battery is not doing so hot if you have a 92AH AGM that is at 60% of its rated capacity after 3-4 years. The Walmart H8 Everstart Maxx's for $130 usually last me around 5 years before needing to be replaced and have an excellent warranty. 900CCA. Depending on the year, they have been the same batteries with the BMW label as there are only a few battery manufacturers left.

You also might want to look at your battery to make sure the dealer actually installed what you paid for. H8 is the largest form factor that fits in the battery compartment; however there are several smaller H7 & H6 variants which would have had lower rated CCAs.

To your alternator problem, though, if you have already tested the voltage output, then I wouldn't even give it a second thought. It's rating is 180A new IIRC and unless you have aftermarket amps or some other high draw items, your battery is charging fine.

[Tambohamilton]

Looks like a bsd line issue to me. The bsd line controls the alternator as well as the water pump, etc. So as per other issues with the bsd line, another component on the line failing could give symptoms or codes for any of the others. Follow the standard procedure of disconnecting components one by one and rescanning for faults/weird voltage.