Originally Posted by angrypengu

And right on cue as Spring is here.

Alright I think I might have figured out *why* BSG's fail a lot more during the winter. I have a device that tells me the vehicle's voltage at any one given point. I monitor this like a hawk.

In the winter, for whatever reason, the car sits at 15.4V for maybe 2 hours for me. This means the DC DC converter is stepping down the voltage to charge the 12V battery. Note: I charge my 12V battery using a trickle charger in the winter and it STILL does this.

When it gets warm, even when the car is started for the first time in the morning, it will only sit at 15.4V for maybe 3 minutes, and then it goes to 12.8V or 13.3V.

This indicates to me that there is probably a correlation b/w why BSGs fail more when it's cold out. I don't know the temperature cut off and I don't know why, but I think there's something here. Interestingly enough even at 15.4V step down in the winter, the torque commanded from the BSG is nothing out of the ordinary, either.

I think the why comes down to this 15.4V thing. I think what is happening is the BSG has more 'drag' on it during the winter and though I can't see anything out of the ordinary force wise being commanded from the BSG, I bet you it's charging the 12V battery for those 2 hours, though at a slower rate.

More torque being commanded = more drag = more heat = more BSG go boom. That's my theory.

Originally Posted by hcuorg

I recall reading a post on Reddit from an Audi Tech that said something similar. But he mentioned since they are liquid cooled, the heat causes leakage so like you said, more heat = more boom. So it's interesting that there seems to be more problems in the winter time. Would think they would happen more in the summer with the added heat.

Originally Posted by angrypengu

Thank you for this data point. What did you mean by "heat causes leakage". I'm not quite following there. Thank you

Also, HOLY SH**, I just remembered. Somebody here posted a long running thread of some electronics wizard taking apart BSGs and he noticed 'burnt' parts. I wonder if there is a correlation here.

Originally Posted by hcuorg

It was this post: https://old.reddit.com/r/Audi/commen...nator_failure/

"Audi tech here. Audi jammed both the starter and the alternator together to create the “starter generator” and since the 48volt battery goes directly to this component it gets very hot. To cool this behemoth of a module down they cool it down with coolant. To nobodies surprise the module has internal leakage issues and will shut down and drain the 12 and 48 volt battery due to no charge coming from the module. Audi really doesn’t want to pay for their stupid mistake and will force us to jump through 7 flaming hoops the size of quarters to get this module replaced even when the vehicle itself knows that the starter gen is the issue. Getting the part can take months because it’s happening to all models A6 and Q7 and above (any vehicle with 3.0 TFSI or above) hopefully the new modules they supply us won’t leak but it’s Audi so I have low hopes"

Originally Posted by angrypengu

Thanks, not sure I agree with that perspective but if he's right the latest BSG probably doesn't fix things. But, he's a mechanic and I'm not, so there is that. (his opinion is more credible than mine)

Originally Posted by Jdsengineer

We've been looking to trade our 2019 A7 with only 24k miles for the last year. I really like the car too, and can't find anything I like better. Lately been looking hard at Genesis G80 sedans. Nice cars, but just a pimped out Hyundai.
In the end, we just drive the A7 locally and hope for the best when it quits.

Originally Posted by angrypengu

And right on cue as Spring is here.

Alright I think I might have figured out *why* BSG's fail a lot more during the winter. I have a device that tells me the vehicle's voltage at any one given point. I monitor this like a hawk.

In the winter, for whatever reason, the car sits at 15.4V for maybe 2 hours for me. This means the DC DC converter is stepping down the voltage to charge the 12V battery. Note: I charge my 12V battery using a trickle charger in the winter and it STILL does this.

When it gets warm, even when the car is started for the first time in the morning, it will only sit at 15.4V for maybe 3 minutes, and then it goes to 12.8V or 13.3V.

This indicates to me that there is probably a correlation b/w why BSGs fail more when it's cold out. I don't know the temperature cut off and I don't know why, but I think there's something here. Interestingly enough even at 15.4V step down in the winter, the torque commanded from the BSG is nothing out of the ordinary, either.

I think the why comes down to this 15.4V thing. I think what is happening is the BSG has more 'drag' on it during the winter and though I can't see anything out of the ordinary force wise being commanded from the BSG, I bet you it's charging the 12V battery for those 2 hours, though at a slower rate.

More torque being commanded = more drag = more heat = more BSG go boom. That's my theory.

Originally Posted by Kilo Papa

IF your theory is correct, would it then stand to reason that those who deactivate the auto on-off function upon every initial start-up would likely not experience BSG failure or at least greatly improve odds of avoiding it?

Based on anecdotal evidence of consistently reading about this issue, I drew the conclusion that shutting off that function would help me avoid the issue or at least defer it for much longer. I have always deactivated auto on/off since purchasing our ‘23. (traded in a ‘21 incorrectly thinking the problem had been corrected in the ‘23 models)

Originally Posted by Kilo Papa

IF your theory is correct, would it then stand to reason that those who deactivate the auto on-off function upon every initial start-up would likely not experience BSG failure or at least greatly improve odds of avoiding it?

Based on anecdotal evidence of consistently reading about this issue, I drew the conclusion that shutting off that function would help me avoid the issue or at least defer it for much longer. I have always deactivated auto on/off since purchasing our ‘23. (traded in a ‘21 incorrectly thinking the problem had been corrected in the ‘23 models)

I really enjoy our Q8 but despise Audi for how they have (not) dealt with this problem.