2008 RS6 avant night time 'beeping'

[TMBi]

Hi. I am the owner of Ross Hobson's 2008 C6 RS6 Avant (bought from him in 2018)and due to some recent health issues the car has unfortunately been laid up SORN for the past 17 months or so, meaning it has been hardly used during that time, even though it has been started and run up to temperature roughly every month. It's fair to say the battery has, on occasion, shown some signs of not being willing to hold a full charge for the complete month or so during that time. Now, though, I'm wanting to get back on the road, and having booked him in for his MOT recently, I put him on charge using my CTEK MXS smart battery charger and after a full charge he started and ran perfectly well, passed the MOT and returned home, but has just developed an annoying problem of starting to beep-beep-beep-beep- (lightly) on occasions (often during the night) together with flashing indicators. a press of the key fob stops it immediately (Fob batteries are brand new) but I'm struggling to understand why it's happening now, even though the battery appears to be perfectly OK and fully charged) It's fair to say it is causing a family rift especially when it happens at 1am
Any help/ advice from anyone with similar experience would be much appreciated,
Many Thanks
Tosh

[Jim Haseltine]

Low batteries on these things throw up all manner of "not a real fault" issues, even if you recharge them via driving for an hour or so they still seem to throw random stuff without a full "out of the car" recharge or a replacement battery (depending on its age).

And he's right - as usual.
However, in addition to that, the batteries inside the alarm unit (on this and other VAG models from the same era) die with little or no warning so that could be your problem.

[IanH755]

To add to the above, do you have the ability to scan the cars ECU for fault codes as it seems like either an alarm sensor is having a bad day or something like a window etc isn't fully up which can cause alarm issues, even if its just open by 1mm.

If you can get the car scanned let us know what fault codes you get, there will probably be a few at least so don't worry, most ECU's are filled with fault codes from transient glitches, what you're after is any fault codes within "Address 46 - Central Convenience" which covers the alarm, all the rest can be reset without concern unless they come back.

[TMBi]

Hi Chaps. Thank you for your help and advice, I tried replying to this thread on my mobile last night but it doesn't appear to have posted properly.
Update: My son has been researching this himself and seems to have found the solution to the problem, apparently the siren unit has a soldered in Lithium battery and if that starts to fail it can exhibit the symptoms i described earlier ( I think this was what as Jim was describing/suggested) - we removed the old siren unit to inspect it - the cost of the batteries and messing about cutting it open, unsoldering and rseoldering the new batteries in was not inconsiderable so we checked the part number against items on ebay and managed to find a pre-used unit from a much later model with an identical part number (thinking the batteries would last a good while longer). cleaned it up to look like new; fitting was fiddly but straightforward and so far, two weeks later, with no recurrence of the beeping it looks very much like the problem's solved. alarm works perfectly, so here's looking forward to getting back on the road asap and enjoying driving him again.

Thank you all again gentlemen for your help and advice.

A very happy Tosh

[HPsauce]

Coincidentally my 2002/3 S8 had very similar symptoms very recently and initially I just took the alarm siren unit out - not that easy as they're well hidden.
It was already a replacement unit (dated 2004) and there's zero chance of finding a decent one now as the design changed fairly soon after manufacture, so I did cut it open.
Inevitably the NiMh batteries inside are also of a design no longer made so there's no "easy swap" option, but I'm working on a solution. It might involve mounting replacements in an external holder and running a cable through the casing, we'll see what's feasible.

[IanH755]

Thanks the update - My Alarm Siren was throwing a fault code for a flat battery back in mid 2022 but mine wasn't beeping or making any noises. MRC ended up replacing the siren pack itself (£200 part No 1K0 951 605 F) rather than attempt the "open/solder new battery/close" method which may have ended up with a dead unit anyway.

[TMBi]

Coincidentally my 2002/3 S8 had very similar symptoms very recently and initially I just took the alarm siren unit out - not that easy as they're well hidden.
It was already a replacement unit (dated 2004) and there's zero chance of finding a decent one now as the design changed fairly soon after manufacture, so I did cut it open.
Inevitably the NiMh batteries inside are also of a design no longer made so there's no "easy swap" option, but I'm working on a solution. It might involve mounting replacements in an external holder and running a cable through the casing, we'll see what's feasible.

You're right, the siren was very well hidden on mine too, but fortunately my son's hands are slightly smaller than mine so he was able to get in to remove the old unit and refit the new one. Like you we had thought about cutting the old one open and doing the replacement that way, but having found the part number we searched on ebay and found a replacement that worked fine from a 2012/2016 model (Q8 I think) so it looks like they continued using the standard part for a few years and we were just lucky to find one, I guess.
Good luck with sorting yours out, though; as you say it may involve a remote power solution or possibly a similar voltage heatshrink wrapped setup inside if you can manage to fit one in.
Cheers,
Tosh