Tom Perkins

Hi there,

I have a 2005 A8 (D3 SWB) 3.0TDI.

The car started going flat back in November and I was unable to diagnose the cause (although I suspected the MMI drain that others have mentioned).

I decided to replace the battery (with a replacement from Audi) and also upgraded the MMI software to version 5570 (in order to work with a newly installed AMI). I'd read that version 5570 solved any issues with power drain from the MMI.

The car's been good since then but yesterday evening when I started the car I got a battery warning message. The car started and drove fine but slightly worrying. Tonight the keyless didn't work when I went to open the boot (I assume the system shutting bits down to conserve battery), I unlocked using the key and started the car normally and again got the battery warning message. Again the car drove fine but seems an issue could be developing.

I didn't get the new battery coded when I bought it (as I didn't think there was much point), but surely that's unlikely to cause battery drain? Or could it be that the car thinks the battery is low when it's not?

Any thoughts on next steps for diagnosis would be welcome (just let me know if there's any extra info you need),

Thanks,

Tom

JulianHicks

Tom; I presume you don't have [or have access to] VCDS. This makes diagnosis quite difficult as scans from the car's ECUs [in particular the Battery Energy Manager - BEM - that's ECU 61] are helpful in 'pointing the finger'.

That being the case, a good starting point is to see if it's a 'real' battery drain by measuring the battery voltage at rest, ignition off.

Fully charged is 12.6V, 75% is 12.3V, 50% is 12.0V, 25% is 11.7V, all approximate and dependent on temperature.

There are 'known' issues with some firmware levels of the A8 BEM that give spurious warnings, but tricky to see on your car without VCDS.

Julian

Tom Perkins

Hi Julian,

Thanks for your reply, I do have a friend that runs a VAG garage and has a VCDS, is that the best place to start?

Thanks also for the battery voltage readings, I'll give the battery a check and see what it reads.

Out of interest, what's your thoughts on getting a new battery re-coded?

Tom

JulianHicks

And BTW; the MMI doesn't 'drain'; it's the battery that drains due to something continuing to operate after the car [and the MMI, 15 mins later] shuts down. And there's lots of 'stuff' in an A8 that might do that sadly!

Not sure where you got the idea that MMI 5570 solved 'battery drains' other than that some really early [0890 ish] levels didn't turn the radio or CD off properly causing a drain. 5570 would have updated the radio and CD firmware so as to resolve these drain issues. If you never had an MMI update, your A8 would have had an MMI from that era. [My 2005 car built Nov 2004 had 0890 until I updated it 9 years ago].

Also, your '2005' car [July 2004 to Jun 2005 build] possibly has one of the 'faulty' BEMs mentioned in my previous post as they were installed in cars from that build year.
For info; the 'bad' levels in A8 BEM ECUs were 0340 0390 0480, HW part 4E0 915 181C. There was a CD based dealer update thet updated it to 0510.

Julian

JulianHicks

The battery is coded purely to indicate to the BEM ECU that it has a 'different' battery. The BEM logs data in the BEM 24x7 [car on and car off] and makes some sort of decisions based on the data is finds from reading the battery condition.
This decision making obviously 'works better' if it logs the right data against the right battery.

I have VCDS so it's an easy choice to code the battery; it's a five min job to code so if you know someone who has a VCDS I'd ask them to recode anyway. Use any battery number if you don't have a 'real' VAG battery.

Not sure it's financialy viable to pay someone to do it though if you have pay more than, say £5.

BTW, VCDS now has a viewer for the BEM logs so if you know someone who has 'proper' VCDS systren at recent levels of software [V17, for example] you can get them to read and print the logs.

Find a VCDS BEM log sample from my 2005 A8 attached. Note that the log also shows my BEM ECU details and indicates the firmware level - 0510. [Mine was a 'bad' 0390 flashed by dealer to 0510].

Julian