pnjriches

For anyone following this post. I think I found and sorted the problem. It appears to have been water ingress from the top of the windscreen. I started to notice a few drops of water on the drivers seat. I noticed the top of the interior trim in front of the sun visor, drivers side, was wet. At the same time I got another problem, this time with the power steering. It became very heavy as if not working at all, then later it was just heavy. Anyway, I eventually sealed the windscreen using some flowable silicone and as the interior has dried out, so the issue with the power steering disappeared and the start/stop went back to being intermittent then disappearing completely. I have since learned that windscreen leaks are common on the A8 (anecdotally) Thanks to all those that tried to help Peter

Thanks for giving this some thought. I have considered this area as well but your comments cause me to give it some more thought. The car was serviced just last month and that was when I had the garage check it out, by that I mean I had this issue and told them about it and asked them to look into it/check it out. Checking the battery is part of the service but I will check back with the garage and ask specifically that the battery check was done and what is was. Also, reading some other forums, battery issues can cause problems with the BEM (Battery Energy Management I think) which can manifest itself as many different things. I think I will put the battery on a charger and make sure it is absolutely fully charged then see how it goes before going to the expense of a new Battery (they aren't cheap). I haven't yet, but I will check the brake light as you suggest. Again, thanks for taking the time and effort to offer your thoughts.

Thanks, but interestingly, it's not intermittent now. It's predictable. the same thing happens each time. It was intermittent at first. When I say that I mean it didn't happen all the time but seemed to occur after there had been rain. Once things dried up, the issue went away and it worked normally. But like I say, the issue is there all the time now. Previously I had a A8 D3 that had a problem with the stability control light coming on after it had been running a while. Also the heated rear screen then stopped working. The main dealer could not solve the problem. The garage I now use sorted it out. It was the alternator affecting the battery computer which in turn caused the issues with the stability control and the heated rear screen, go figure. The same garage has looked at this problem and as yet do not have an answer for me. Hence the reason for reaching out. Thanks again

Thanks for your suggestions, tried them all and others. The auto electrician I had look at it told me there was not a fault code coming up. Like I said, it's a strange one.

My 2011 Audi A8 has an issue when starting. It was working as it's supposed to, foot on the brake, press the button and then Pesto it starts. Then it started playing up. Initially, sometimes when I would put my foot on the brake and press start it would start but I would get an error warning that the start/stop was not working. This tended to happen after there had been rain. Now it is a problem all the time. If I press the brake, then press start once the ignition comes on but it doesn't start. If I press the button a second time (with foot on brake) it starts but with the warning that the start/stop isn't working. If I press it once (foot on or off the brake) then with foot off (if it was on) press it a second time to turn the ignition off, then foot on brake, press the button, it starts and the start/stop is there. Go figure. Anybody got any ideas? I talked to the garage I use but they had no idea.

My 2011 Audi A8 has an issue when starting. It was working as it's supposed to, foot on the brake, press the button and then Pesto it starts. Then it started playing up. Initially, sometimes when I would put my foot on the brake and press start it would start but I would get an error warning that the start/stop was not working. This tended to happen after there had been rain. Now it is a problem all the time. If I press the brake, then press start once the ignition comes on but it doesn't start. If I press the button a second time (with foot on brake) it starts but with the warning that the start/stop isn't working. If I press it once (foot on or off the brake) then with foot off (if it was on) press it a second time to turn the ignition off, then foot on brake, press the button, it starts and the start/stop is there. Go figure. Anybody got any ideas? I talked to the garage I use but they had no idea.

I had a similar issue with my A8 D3, the light would come on after the car had been running a while. I noticed it did this less in summer than winter. The Audi dealer had a look but could find nothing. I also noted that the heated rear screen stopped working. Anyway, just before I sold it I put the car into a local independent garage and they suggested the reason was the alternator in combination with the battery computer. Sounded like mumbo jumbo to me. I decided to have the suggested work done, which was to change the alternator and if that didn't work to change the battery computer. They changed the alternator and hey presto the problem was solved. I had researched this problem for a while and found nothing on any of the forums, some suggested wheel sensors or brake light sensor or steering sensor so I guess this problem could be associated with other issues. so I am not suggesting this is the only reason for the light to come on or the only cure. But it does show up the short comings of the main dealer. Hope this helps