Alternator woes...

[Danzzo]

Hey guys... Last night while driving into my apartment complex, I got the dreaded "Alternator fault. Battery not charging".

Pulled the battery and took it to AutoZone that same night, battery tested good (only 2 years old) at 12.4v and 45% charged.

I then went home and put the battery back in the car and took a voltmeter to it. Without the car running, batter between the post was reading 12.x. With the car running, battery was reading 10.3/10.6.

This morning I went and swapped the alternator at pepboys for a remanufactured one. Put it in, put the belt back and and started it up and everything appeared fine.

Tested the car without it running and it's getting 12.6v between the post. With the car idling I'm getting 13.3/13.6.

My issue is now that I've been driving the car literally all day today making my normal errands and no warning lights and the car is running fine. When I use carista to check for codes, I'm still getting Can Network Gateway codes:

02071 - Local Data Bus
02252 - Generator
00458 - controller for battery monitor (J367)

No matter how many times I clear the codes, they keep coming back instantly. These were the same codes as when I originally got the alternator light (that came with the dash warning).

What gives? Does the ECU needs time to reset or is my renan alternator faulty?

[PedroA4]

I’ve had an under post code one time that would t go away until I drove the car for a while.

[Danzzo]

In the below picture, should I have taken that nut off? When I originally installed it, it came with two nuts stacked on top of each other. I took the one but off, put the ground cable on top of the nut that was still sitting in there, and then sandwiched the other but on top of the ground cable.

Could still be causing my low voltage issue?

[Stazi]

In the below picture, should I have taken that nut off? When I originally installed it, it came with two nuts stacked on top of each other. I took the one but off, put the ground cable on top of the nut that was still sitting in there, and then sandwiched the other but on top of the ground cable.

Could still be causing my low voltage issue?

No. That would not affect anything

[Danzzo]

So I went out and tested with the voltmeter again.

This time I ran the test on the positive and negative posts inside the engine bay versus the battery in the trunk. For the most part, the posts inside the engine bay read at a steady 13.00v (though dropping to 12.4 and 12.7 with running all accessories) with the engine running and the battery in the trunk read at a consistent 12.7v. with the engine off, the battery is ready 12.22v.

Still stumped as to what is causing the low voltage, though I still have no alternator notification in the dash.

Any suggestions or help? Or are these numbers in spec with a battery that's charged at 45% even though I've been driving all day (was 45% yesterday as well for reference)

Btw, the new alternator was benched tested before buying and it was good. AutoZone tested it today and said the alternator was reading bad, though they couldn't tell me what bad meant. The alternator is 140amps.

[Theiceman]

Yeah 12.4 -12.7 under load is not very good..

Sent from my SM-G973W using Audizine mobile app

[ELaw]

Btw, the new alternator was benched tested before buying and it was good. AutoZone tested it today and said the alternator was reading bad, though they couldn't tell me what bad meant. The alternator is 140amps.

Which alternator was tested today? The original one, or the replacement? If the replacement alternator tested bad, there's your answer! It's rare, but possible that it would test good at the time it was sold, but have some sort of failure shortly after installation.

If not, here's an idea if you can pull it off: measure the voltage right at the alternator output terminal with the engine running. Obviously you have to be very careful doing that, because of moving parts and also because there's enough current to do really nasty things if your meter probe accidentally shorts between the output terminal and ground. Also when you do it, put the meter negative on a good clean ground point on the car chassis, not the engine.

If you read good voltage (13.8 volts or more) at the alternator output terminal but much less at the jumper cable connector, you've got some kind of voltage drop between the alternator and the jumper cable connector.

If you read low voltage at the alternator output, the most likely cause is a bad alternator. But the engine ECU can tell the alternator to reduce its output voltage so it's possible that is happening for some reason.

[Danzzo]

Which alternator was tested today? The original one, or the replacement? If the replacement alternator tested bad, there's your answer! It's rare, but possible that it would test good at the time it was sold, but have some sort of failure shortly after installation.

If not, here's an idea if you can pull it off: measure the voltage right at the alternator output terminal with the engine running. Obviously you have to be very careful doing that, because of moving parts and also because there's enough current to do really nasty things if your meter probe accidentally shorts between the output terminal and ground. Also when you do it, put the meter negative on a good clean ground point on the car chassis, not the engine.

If you read good voltage (13.8 volts or more) at the alternator output terminal but much less at the jumper cable connector, you've got some kind of voltage drop between the alternator and the jumper cable connector.

If you read low voltage at the alternator output, the most likely cause is a bad alternator. But the engine ECU can tell the alternator to reduce its output voltage so it's possible that is happening for some reason.

Hey! Thankd for the reply! How would I test at the alternator? Also, the new alternator was bench tested, not the old one.

Side note, would anyone know at what volt the ECU will throw the alternator faulty? Still haven't gotten it yet after about 4 hours of driving...

[Smac770]

The codes are not saying anything about the operation of the alternator output. They are saying the LIN bus that connects the CAN Gateway, the alternator voltage regulator, and the battery energy management module is not functional. It would be more helpful to those of us you're asking to help you to post the complete DTC text. I assume it looks something like:

02071 - Local Databus 
            012 - Electrical Fault in Circuit
02252 - Generator 
            004 - No Signal/Communication
00458 - Control Module for Battery Monitoring (J367) 
            004 - No Signal/Communication

The best next step would be to unplug the voltage regulator and clear the codes and see what comes back.
Then plug that back up and unplug the BEM (the two-wire plug on the device on the negative post on the battery) and clear codes and see what comes back.

The assumption is, unless the problem is in the CAN Gateway itself, is there's a problem with one of the two LIN slaves or with the wiring to them. With one unplugged, the other should work again. The question being which one works when the other is unplugged.

[Danzzo]

The codes are not saying anything about the operation of the alternator output. They are saying the LIN bus that connects the CAN Gateway, the alternator voltage regulator, and the battery energy management module is not functional. It would be more helpful to those of us you're asking to help you to post the complete DTC text. I assume it looks something like:

02071 - Local Databus 
            012 - Electrical Fault in Circuit
02252 - Generator 
            004 - No Signal/Communication
00458 - Control Module for Battery Monitoring (J367) 
            004 - No Signal/Communication

The best next step would be to unplug the voltage regulator and clear the codes and see what comes back.
Then plug that back up and unplug the BEM (the two-wire plug on the device on the negative post on the battery) and clear codes and see what comes back.

The assumption is, unless the problem is in the CAN Gateway itself, is there's a problem with one of the two LIN slaves or with the wiring to them. With one unplugged, the other should work again. The question being which one works when the other is unplugged.

So with the bem unplugged and the alternator plug still connected, all 3 original codes were still present.

With the bem connected and the alternator plug disconnected, only the 02252 - Generator code is present and no other codes present (the other 2 codes went away)

What does that tell me?

[ELaw]

Hey! Thankd for the reply! How would I test at the alternator? Also, the new alternator was bench tested, not the old one.

The best way I know to test the alternator is as I indicated in my post: test the output voltage at the alternator with the engine running - if you can do so safely.

But from the other posts here, it's sounding more like a communication/networking issue than a simple bad alternator (although if the alternator failed in a certain way it definitely could cause those errors).

I'd suggest doing what Smac770 said: try running the car with the LIN bus connection to just the alternator disconnected, just the connection to the battery monitor disconnected, then with both disconnected, clearing codes and then checking them each time.

One thing I can say from experience is that codes indicating faults on LIN bus nodes are not always correct. On my car I had a situation somewhat like yours, where I got a message and codes indicating the controller for the wiper motor (which is integrated with the motor itself) was bad. I replaced the motor and it did not solve the problem. It turns out the motor, the rain/light sensor, and the central electric module are networked together, and when I disconnected the rain/light sensor the problem went away! The moral of the story being that if codes indicate a communication fault with one of several networked items, the fault doesn't always lie with the item the code says.

[Danzzo]

The best way I know to test the alternator is as I indicated in my post: test the output voltage at the alternator with the engine running - if you can do so safely.

But from the other posts here, it's sounding more like a communication/networking issue than a simple bad alternator (although if the alternator failed in a certain way it definitely could cause those errors).

I'd suggest doing what Smac770 said: try running the car with the LIN bus connection to just the alternator disconnected, just the connection to the battery monitor disconnected, then with both disconnected, clearing codes and then checking them each time.

One thing I can say from experience is that codes indicating faults on LIN bus nodes are not always correct. On my car I had a situation somewhat like yours, where I got a message and codes indicating the controller for the wiper motor (which is integrated with the motor itself) was bad. I replaced the motor and it did not solve the problem. It turns out the motor, the rain/light sensor, and the central electric module are networked together, and when I disconnected the rain/light sensor the problem went away! The moral of the story being that if codes indicate a communication fault with one of several networked items, the fault doesn't always lie with the item the code says.

I would like to test at the alternator post but how would I do that? Also, see my note above. I ran the test regarding the removal of the bem plug and alternator plug. With the bem plug removed and the alternator plug connected, all codes remained. With the alternator plug removed and the bem plug connected, only the 02252 (generator) code was present.

Here are some numbers from today all from the battery posts:

Car off: 12.4v
Car running at idle: 13.1v
Car running at idle with all accessories and ac full blast: 12.7v/12.9v

Still have no alternator light or DIS notifications and the car is running fine. I can't tell if these numbers are decent or not but I assume that if it wasn't, the car would throw the alternator light..

[ELaw]

I would like to test at the alternator post but how would I do that?

I'm not sure I understand the question? You test it the same way you'd test voltage elsewhere... set multimeter to volts, put negative meter lead on a good ground (preferably on the body), and the positive meter lead on the output terminal of the alternator. That's assuming you can get to the output terminal safely with the engine running... I've never actually tried it on one of these cars.

Honestly though, this is sounding more and more to me like the replacement alternator is bad. When the store tested it, it's 99.9% likely they just spun it with a motor and checked that it was producing some power - it's very unlikely they have the ability to test bus communication with it. So it may appear "good" to them even though the regulator has a problem on the communication side.

[Gunnark100]

Car off: 12.4v
Car running at idle: 13.1v
Car running at idle with all accessories and ac full blast: 12.7v/12.9v

Still have no alternator light or DIS notifications and the car is running fine. I can't tell if these numbers are decent or not but I assume that if it wasn't, the car would throw the alternator light..

These numbers are not ok, but you will not get alternator error with those! Test alternator like Elaw said above.

[Danzzo]

Update. Installed a new alternator at the pep boys parking lot. Took all but 10min.

With it first installed and engine running, I was pushing out 13.7 volts. With all accessories and AC on, I was still pushing 13.7 volts with little to no fluctuating. All codes have disappeared accept for the 02252 (generator) code.

Drove 10min home and checked it and it's only putting out 12 volts with the engine running and 11.9 volts with the engine running and all accessories and fan on.

Does Audi have some kind of voltage management thing going on here? What is everyone else getting when you check your voltage with the car running?

And I still have the 02252 generator code.

[ELaw]

Do you think there's any chance they gave you the wrong alternator (twice)?

There definitely is battery-management functionality in our cars. The engine ECU (I think?) talks to the alternator over the LIN-bus connection we've been discussing and sets the alternator's output voltage. The 02252 code indicates that communication is not taking place, so the alternator probably goes to some default output setting.

[Danzzo]

Do you think there's any chance they gave you the wrong alternator (twice)?

There definitely is battery-management functionality in our cars. The engine ECU (I think?) talks to the alternator over the LIN-bus connection we've been discussing and sets the alternator's output voltage. The 02252 code indicates that communication is not taking place, so the alternator probably goes to some default output setting.

One thing I noticed is that the plug connector, though it fits, it doesn't seem like it stays in in. I could easily pull it out with a finger. The other one was a snug fit but never "snapped" in. I wonder if that could be something

[ELaw]

That's a red flag for sure!

Do you still have the original alternator (not the first replacement, the one that came with the car)? If so, maybe pull the new one off, place both on a bench, and carefully compare them to see if they're the same.

[Danzzo]

That's a red flag for sure!

Do you still have the original alternator (not the first replacement, the one that came with the car)? If so, maybe pull the new one off, place both on a bench, and carefully compare them to see if they're the same.

I unfortunately don't. Turned it in as a core. Would it be worth it to just buy a used alternator on eBay? They're going for under $100 for oem ones but not sure how much life they have..

[Danzzo]

Another update. Car sat for about 2 hours.

Just went out to test for the hell of it.
Car running: 13.4 volts
Car running with full accessories and ac on LO: 11.9 volts

Turn car off then immediately back on:
Car running: 13.3v/13.5v
Car running with all accessories and ac on LO: 13.2v/13.3v

Why would restarting the car fix the voltage issue?

Also, with the above numbers, is it worth it to just get a used oem alternator off eBay for $80? Or are the above numbers within spec of an alternator at idle? When I press the gas I do get higher voltages.

[Smac770]

That the codes clear up when you disconnect the voltage regulator LIN bus connection (other than the given can't talk to the device you unplugged code) implies to me there's a problem with the voltage regulator or the wiring to the voltage regulator (or as you noted, maybe a plug issue). The voltage regulator is a separately orderable part; there's not a need to replace the whole alternator to change out the voltage regulator. Though if you bought an alternator and can't replace just the voltage regulator, I guess swapping whole alternator is what you'd need to do.

https://www.ecstuning.com/b-genuine-...tor/07k903803/

If you were looking at a used OEM, I tend to like Wolf Auto for used parts:
https://wolfautoparts.com/audi/2009/...generator.html


The voltage regulator should have a fall back program in the event of loss of LIN bus management. So even with the voltage regulator unplugged, the alternator should be putting out better 12v. Something like:

Default mode
This mode is equivalent to the “Regulation with LIN” mode except that the default parameters (VREG, LRC rate, LRCDISF,...) are used for regulation, as there is no LIN communication. These parameters are programmed at the end of line testing. When there is no valid frame for more than LIN timeout, regulation voltage target transitions to default VREG with a ramp of 0.2 V/s (± 10 %) and excitation limitation value transitions to “no limitation” (equivalent to a 12.7 A limitation value) with a ramp of 0.375 A/s (± 10 %). If communication resumes with RX frames, equalation voltage target and current limitation changes with no delay to their respective values set by LIN.

But not sure what that Vreg value would be. I would be more interested if things seem fine with the voltage regulator unplugged, rather than connected knowing there's defective LIN communications with it occurring. It might be thinking it's seeing valid low set point LIN commands when they are actually just random static.


You might check the voltage regulator harness plug terminal for any short to ground or 12v, or corrosion, or maybe it's not even sitting in the plug correctly at this time.

C1 (voltage regulator) pin 1 -> T17r pin 11 -> joins with wire from J367 (BEM) pin 1 -> T17e pin 15 -> J533 T20d pin 2

T17e is the red 17-pin connector in the bottom of the A-pillar, ie behind the driver's side kick panel. This connection point is between the J533 and the BEM and VR, so not likely a concern.
T17r is the white 17-pin connector in the ECU box. This connection point is specific to the wiring path to the VR. You should probably check it, maybe unplug and replug it in case there was corrosion build up or just bad terminal seating.

[Danzzo]

Another update. So yesterday I was driving the car when the red battery sign started to flash and the alternator not charging message showed. At this point, I took it directly to a Audi specialist. They changed out he alternator with an OEM alternator and have verified that the alternator is now pushing out 14.xx volts.

That's the good. The bad is that the battery is still not not being charged (showing 12.xx volts when the car is running). They verified that the wiring from the alternator to the battery is good and that all of the fuses checked out. Their next step is to take apart the dash to find some kind of module that may be the issue.

What module under the dash could be causing this issue? Any other suggestions as far as checking out other places? Does the B8 A4 have an exciter wire in the dash that could cause the battery not to charge but the alternator to work fine?

[ELaw]

What module under the dash could be causing this issue? Any other suggestions as far as checking out other places? Does the B8 A4 have an exciter wire in the dash that could cause the battery not to charge but the alternator to work fine?

Nothing... those people are clueless.

For electricity to flow there must be a complete circuit. For example in a flashlight (an oversimplified one with no switch) the circuit is battery positive terminal -> light bulb terminal -> light bulb -> other light bulb terminal -> battery negative terminal.

In our cars the charging circuit is: alternator positive terminal -> terminal block with the jumper cable connection near the base of the windshield -> battery positive terminal -> the battery itself -> battery negative terminal -> battery current monitor module (in the trunk) -> connection to car's frame -> frame of the car -> wire from frame of car to engine block -> engine block -> alternator case which is its negative terminal.

If the alternator is putting out 14 volts (as measured at the alternator) there has to be a problem somewhere else in that circuit that's preventing the current from making it to the battery. You just need to check every segment of the circuit to find where the fault is.

One other thing I'll toss out is that if the battery is far from fully charged, there can be a small voltage drop between the alternator and the battery. So if you see 14.0 volts at the alternator you might see 13.5 at the battery. But that drop would eventually be reduced as the battery reaches full charge and draws less current.

[Danzzo]

Just called them back and asked specifically what they are checking for. they stated that they are checking the 'Data Bus On Board Diagnostic Interface module' which is in the center of the dash. Everything else checked out. The alternator is making 13.9v/14.3v, but the battery is still not getting a charge. Everything else was checked and all grounds are cleaned and checked. They said that something in between the alternator and battery is causing the issue despite all connections, grounds and wiring being fine.

Any truth to the"Data Bus On Board Diagnostic Interface module" theory?

[Novarider]

Did the battery go bad? I'd try a new battery before I paid them to rip into the dash.

[Danzzo]

They claim the battery tested good as well as tried a new battery and got the same results. I'm really losing my head over this whole thing.

[Smac770]

That's the J533, the LIN master on that LIN bus connecting the voltage regulator and the battery management. It's what tells the voltage regulator what to output, along with many other things it does. I don't know why they'd be looking at that module. The J519 and the J393 are the two big consumer managers. Getting to the J533 is simple. Remove the glove box and there it is.

I'd start the car and let it idle a few minutes to stabilize the battery after the drain of starting it. Turn off consumers such as the radio, the climate system, the DRLs. There's three positive points of interest and three ground points of interest to start with. You've got the B+ post and the housing of the alternator, the + and - jumper cable posts under the hood (+ is in the center of the plenum, - is on the left strut tower), and the + and - posts on the battery itself. I'd get a pair of long leads (so you're using the same ones the whole time) and make a chart of all the voltage readings from each position to each of the other five positions (so yeah, that's a lot of readings). See if anything stands out as unexpected.

Additionally, make sure to jump into measuring blocks on the CAN Gateway (address 19, aka the J533) and see what the car says it's telling the alternator to output (block 14 I think) and what the car thinks the battery's voltage is (block 18 I think). Other blocks you should log values of would be pretty much 1 and 14 through 22 (?). Additionally, you should see the generator output current and the battery charging current. Any voltage drop from the generator B+ to the battery +, divided by the charging current, would reflect the resistance value along that path. It should not be significant, or you've got an issue along the way. But somewhere in all that should be something that stands out as unexpected.

But then again, maybe your issue is a wiring short/open issue, corrosion, poor connection, etc. You were fine for a while and then it popped up. Maybe something heating up due to connectivity issue and creating a problem? Keep in mind the cable from the generator B+ does not go to the battery. It goes to the starter. And then it goes to that jumper cable block in the center of the plenum (so any voltage drop from the B+ post to the + jumper cable post would be undesirable). Then it makes the run to the fuse panel A (that big block on the battery + post) and then finally contacts the battery + post.

[ELaw]

Any truth to the"Data Bus On Board Diagnostic Interface module" theory?

The way they've described it, no!

As you probably know our cars have several "CANbus" networks in them. The diagnostic module is where all the buses come together. It can (pun intended) regulate what data flows between the CANbuses, but does not sit between the alternator and battery in any way. With the exception of a couple of things that are functionally almost the same as wire (jumper cable connection block, battery current monitor, the car's frame, the engine block), the only thing between the alternator and the battery is wire.

And... the connectors. This is a stupid thing but but have you tried putting a meter directly on the battery terminals vs. putting it on the cable ends that go on the terminals, and see if there's any difference?

[Smac770]

Oh, and when you've got any probe on that B+ output post on the generator, really make sure it doesn't touch anything else, ie, the entire rest of the generator. Or anything else for that matter. Or you'll have a really bad day.

[Danzzo]

I just called the mechanic back and relayed some information to him. Told him about the J533 location and also asked about he battery just to confirm. Battery tested good as stated earlier. I've been doing a lot of reading up on this issue and it looks like if you don't have the exact alternator and regulator, this could cause all of the issues.

I have a picture of my old alternator and gave him the part number for it. If you guys have any more tips, i'd be glad to relay it to him no matter how annoyed he may be getting..

[ELaw]

Actually IMHO you're part right and part wrong.

Having the wrong alternator could definitely cause a problem, and that may have been the case earlier. But the alternator's responsibility is to provide the correct voltage at its output terminal and it sounds like it's now doing that.

If the alternator's output voltage as measured right at the alternator is 14 volts and there's any less than 13.5 at the battery, there's something wrong in the wiring/etc. between the alternator and the battery. Although i the car starts fine, at least for a first pass that rules out a lot of things because the alternator and starter share a lot of the same circuitry between them and the battery. The one thing they do not share is the cable going from the alternator output terminal to the starter...

Edit: I don't suppose the starter was replaced recently? Or any other work done that involved the starter? If the alternator-starter cable was removed and not reinstalled properly, it could explain what's going on.

[Danzzo]

Actually IMHO you're part right and part wrong.

Having the wrong alternator could definitely cause a problem, and that may have been the case earlier. But the alternator's responsibility is to provide the correct voltage at its output terminal and it sounds like it's now doing that.

If the alternator's output voltage as measured right at the alternator is 14 volts and there's any less than 13.5 at the battery, there's something wrong in the wiring/etc. between the alternator and the battery. Although i the car starts fine, at least for a first pass that rules out a lot of things because the alternator and starter share a lot of the same circuitry between them and the battery. The one thing they do not share is the cable going from the alternator output terminal to the starter...

Edit: I don't suppose the starter was replaced recently? Or any other work done that involved the starter? If the alternator-starter cable was removed and not reinstalled properly, it could explain what's going on.

As far as i'm aware, no work was ever done on the starter. I tap the fob in the slot once and it always starts right up immediately..

[Smac770]

For a US B8.0 A4, the only correct alternator would be Audi 06H 903 016 L (LX is same thing but a reman) aka Bosch AL0891N (AL0891X is same thing but a reman). Nothing else.

[Danzzo]

Update: the mechanic at the shop I took it too didn't fix the problem either after spending $1500. He installed a "Bosch" alternator but when I checked the part number, it was a pepboys p/n.

I switched the battery out today with a brand new one and I'm now getting 13.2v while running and 12.5v when the car is off and all codes from my OP are still present after clearing and checking again.

I just ordered a OEM Bosch alternator (https://www.fcpeuro.com/products/aud...40-amp-al0891n) from FCP Euro and I hoping this solves this problem once and for all.

After doing hours of research, it looks like Audi's don't take kindly to aftermarket or "auto stores" voltage regulator and this could be causing the issues (is this true?)

Also, FCP euro had two alternators, this one that I bought (https://www.fcpeuro.com/products/aud...40-amp-al0891n) and this one: https://www.fcpeuro.com/products/aud...vag-06h903016l

Are they the same thing? I'm on my third "new" alternator now and I'm just fed up. Please let me know if I should cancel my order and go for the VW/Audi version instead..

[Smac770]

I already told you the Audi part 06H903016L and the Bosch part AL0891N are the same thing. Audi doesn't make alternators, but they source parts, manage inventory, and need their own numbers. Same for that Pep-Boys alternator. You don't care what Pep-Boys calls it, you care what Bosch calls it. What was the Bosch part number on that Pep-Boys alternator? It doesn't matter what anyone else calls it when they stock it so long as Bosch called it AL0891N when Bosch built it. I'd never pay the unnecessary mark up for a Audi 06H903016L when I can just buy a Bosch AL0891N. Same thing for the high pressure fuel pump. I'd never pay the extra for a new Audi 06J127025J when I can just buy the Hitachi HPP0010, which is exactly what Audi is sourcing and marking as their 06J127025J (though J has been superseded by L now and not sure what's actually changed).

You've swapped in enough batteries and alternators that I think you need to start tracing the wiring. Did you ever create that map of voltage drops like I told you to?

[Danzzo]

I already told you the Audi part 06H903016L and the Bosch part AL0891N are the same thing. Audi doesn't make alternators, but they source parts, manage inventory, and need their own numbers. Same for that Pep-Boys alternator. You don't care what Pep-Boys calls it, you care what Bosch calls it. What was the Bosch part number on that Pep-Boys alternator? It doesn't matter what anyone else calls it when they stock it so long as Bosch called it AL0891N when Bosch built it. I'd never pay the unnecessary mark up for a Audi 06H903016L when I can just buy a Bosch AL0891N. Same thing for the high pressure fuel pump. I'd never pay the extra for a new Audi 06J127025J when I can just buy the Hitachi HPP0010, which is exactly what Audi is sourcing and marking as their 06J127025J (though J has been superseded by L now and not sure what's actually changed).

You've swapped in enough batteries and alternators that I think you need to start tracing the wiring. Did you ever create that map of voltage drops like I told you to?

Well I just checked the alternator and the part number for the "Bosch" unit they put in was: 23255, which is a Wilson remanufactured alternator from pepboys.

Doing some research on this part number, it looks like it's interchangeable part numbers are:

439393
V10-13-44320
V10-13-46180

On the pepboys site (https://www.pepboys.com/wilson-alter...73465?tab=tab4) it says that it's a Bosch reman and is a direct fit for a 2009 A4. But on the eBay site (https://www.ebay.com/itm/Alternator-...8AAOSwi1pblAzD) it lists the interchangeable part numbers above.

At this point, all I've had we're the part stores alternator and none of them work. Even when the idiots at the shop put in a new "Bosch" unit, it turns out that it wasn't an oem or oe Bosch unit, just a Wilson unit from pep boys, again.

Every test I and the shop did was fine, the only thing I have not done was verify the output at the alternator in fear of Smac770's previous warning about not touching anything else or bad things can happen, though, the shop "verified" the alternator output and says it's pushing out 14v.

My assumption is that the alternator is pushing out 14v on the bench, but when it gets installed, the voltage regulator doesn't want to play nice since it's not an oem or oe Bosch voltage regulator and the car doesn't like it or somehow, recognize it.

[ELaw]

Are you still getting any fault codes indicating trouble communicating with the alternator?

If yes there may be other things going on, but if not you need to start checking voltage drops as I and others have suggested.

[Spawne32]

Has the battery current sensor been replaced...

[Danzzo]

Are you still getting any fault codes indicating trouble communicating with the alternator?

If yes there may be other things going on, but if not you need to start checking voltage drops as I and others have suggested.

Yes, I am still getting the same fault codes as before:

02071 - Local Data Bus
02252 - Generator
00458 - controller for battery monitor (J367)

[Spawne32]

Yes, I am still getting the same fault codes as before:

02071 - Local Data Bus
02252 - Generator
00458 - controller for battery monitor (J367)

I mean the last code there is plainly "Battery Regulator - No response from controller"