A6 Idle Current Problem

"I'm having a problem with my A6 where the battery keeps draining every few months if the car sits for a while. Currently, I'm measuring a quiescent current of 6 mA, but when I read the historical data with the new VCDS Beta, I see that there's often an elevated quiescent current. The problem started around the time I updated the MMI, and it was quiet for a long time, but now it's happening again occasionally, where the battery is drained if the car isn't driven for a long period."

Record 2/18: No-load current exceeding the specified range.
2017-06-27, 13:53:34*0000*06.12*001
2017-06-19, 08:45:42 *0118* 00.48* 001
2017-06-18, 11:01:19 *0000* 01.10 *001**
2017-06-13, 20:46:08 *0087* 00.48 *001**
2017-06-13, 12:51:40 *0003* 00.47* 001**
2017-06-12, 21:47:32 *0009* 00.47* 001**
2017-06-12, 18:42:29*0000*04.34*001
2017-06-12, 13:51:43*0000*00.47*001
2017-06-10, 13:51:49 *0035* 00.47* 001**
2017-06-09, 21:15:55 *0011* 00.47 *001* 02519***

So, on June 19th, he had a quiescent current of 0.48 A for over 118 hours.

I vaguely remember that somewhere in the SSP documentation, there's an explanation of how to interpret the numbers. Does anyone have the number of the SSP document?

chli1976 wrote:

From time to time, it happens that if it hasn't been moved for a while, the battery is empty.

What does that specifically mean in terms of days or weeks?

It varies...
It had been almost a year of inactivity, and the last time it was running, it only lasted a week before the battery died.

SSP 364 might be able to help you.

Thank you, @Wiesel.

I actually thought that a control unit was causing this quiescent current.

According to SSP, there cannot be any control unit on the CAN Comfort bus; this means it could be on the CAN Powertrain and Infotainment bus, or on some other "normal" consumer device.
Furthermore, it should be possible to disregard all entries with 000 or 001 hours.
But if it's drawing 6.12A for 59 minutes, that's still quite a bit of current. That would certainly be hard on a new 80Ah battery, but this one has already suffered.

Does a CAN drive/infotainment system that is not in sleep mode activate the CAN comfort function? But if so, the current draw would certainly be more than 0.5A.

Now the question is how I can best figure this out. If I'm starting with 12V, that means the corresponding device is only consuming 6 watts of power.

How does the radio clock work? If it's turned off in the MMI, does it still synchronize? As far as I can remember, it seems to synchronize sometime in the evening.

Hi chli1976.

I had the same problem with my 4F, even with new Varta Silverdynamic 110Ah batteries.
In my case, the problem was with the battery management control unit, or BEM.
The control unit with the part number 4F0 915 181 A and the software version 4F0 910 181 E - just like with yours - often causes problems in other 4F vehicles as well.
After a certain age of operation, these errors occur. If you were to create a log using a VAS tester, which allows test routines to be run, you would see that it is a "data bus wake-up" issue. At least, that is my limited information.
Sometimes, when I went back to the garage in the evening, the warning light was still on, which, for me, meant that there was no communication bus activity.
The battery was also losing its charge more and more, so I had to recharge it every three days.

Apparently, it's known within the company that there are issues with part number 4F0 915 181 A, but the solution being offered is only a new BEM (presumably a replacement part or module).
with a reference to different software. Of course, no exchange or goodwill .

I simply bought a used BEM NR 4F0915181B from the facelift models starting in model year 2008, with a modified SW 4F910181F. I got it from a recycling center for €105.

Disconnected the battery, charged it, then installed the Battery Management System (BMS), encoded the battery size/type, and it's been fine ever since. There have been no more problems, and the battery is always fully charged, no matter how long it sits.
The starting speed has also been consistently and noticeably higher since then.
The bus automatically enters a silent mode exactly 90 seconds after starting, and the light will then turn off.

The difference between the Ah discharge and the buffered Ah of the alternator is practically 0Ah.
With the old BEM system, the amount of charge stored in the Lima battery gradually decreased, while the amount of charge consumed increased, ultimately leading to a discharged battery.

I hope this helps you a little.

Regards,
Mpire

Okay, here's the translation:

Thank you.
Yes, I also received an update from BEM when the issue started.

I have a contact who might be able to provide access to a VAS tester. Do you know which test routine that is, or what the name of that test is?

There are several tests that should be performed in the following sequence. You should plan for about 2 hours to complete all the tests and analyze the results.


A-battery check.
C generator testing.
Historical data.
Identification.
Idle current measurement.

These 5 tests provide approximately 6 pages of data .

Your update for the BEM (Battery Energy Management) cannot lead to success because the hardware has also been changed. While the software runs on the old BEM, the error persists.
I opened both BEMs before installation, and the components and the circuit board were slightly different .
The BEM switch has already helped many other people with the same problem.
If I had figured it out sooner, I wouldn't have suffered through those cold winter nights.

Regards,
Mpire

Okay, here's the translation:

Thank you.
I'll get one!