ACC/Brake Guard unavailable - weird way it triggered

[Rykenroll]

Hello everyone. I've been a 'lurker' for a while here and this is the first time I'm creating a new post. So here it goes!
My car is a 2012 A6 Prestige. Love this car! A weird thing happened and am asking for the group's help in resolving.
Car was parked but running and I got out to put a letter in the mailbox. When I returned, the dash warning symbol was lit and the cluster said ACC/Brake Guard unavailable. That seemed really weird as everything was working normally up to that moment.
Did VCDS and it said the driver's door switch was at fault. Okay, I guess I need to replace that part someday. Sometime in the next month, the fault disappeared. No idea why. VCDS still showed the driver's door switch to be the problem yet ACC worked perfectly. Maybe some electronic gremlin came and went.
Months later it happened again but slightly different. I left the car (it was shut off) and my daughter hit the ignition button so she could listen to the radio. When I got back, the warning was on. Later checked VCDS and had the same driver's door switch fault. A few weeks later it 'fixed' itself again. Baffling!!
Now I was aware that if the car is running or if the ignition is on and the driver leaves the seat, this warning will come on. Unfortunately, I didn't tell me wife that and recently I left the car and she hit the ignition button to listen to the radio and now the warning is back.
I use cruise control a lot so not having ACC is upsetting. ACC normally works great and the sensors are aligned properly and all other electronics work correctly.
So Audizine friends, below are my questions. Can anyone help please???
Thanks a lot.
Ryan

1) Has anyone else ever come across the ACC/Brake Guard become unavailable because the driver was absent and the car was running or the ignition switch was turned on?
2) Any idea why that would have triggered the warning?
3) Any suggestions for how to fix this so the computer re-instates the ACC? Besides replacing the driver's door switch (which I may do eventually).

[bahula03]

Haven't experienced it myself, but have seen it mentioned with enough frequency to know that it's an "answer's in the question" kinda deal. A little bit of searching or someone that's resolved the issue will get you the full answer, but that switch (or maybe the wiring to it) shorts to ground and creates an implausible signal, and with the way Audi wrote the software, that's enough to disable the systems in question. Gotta fix the thing to have ACC reliably available.

[Wilbur_RS7]

Have you thoroughly cleaned the sensors in the front bumper? Mine would randomly stop working as I was driving, or when I first started it up, and so on. No reason at all. They'd usually start working again until one day they didn't.. So I took out the 2 front grilles and cleaned them about 4 times over. Been fine ever since... Probably not your issue but could be something very simple.

[DGr1FF]

I had intermittent ACC/Brake guard sensor dash light some months back. My sensors were not screwed in and braced firmly, so they had some wiggle room. Seemed the sensor may have been getting blocked while driving.

[Rykenroll]

Thanks for responses so far. I'll check for secureness of the sensors and clean them. That has not been done before. I did search previously for ACC issue and there were lots of posts but nothing seemed related to it triggering when the driver leaves the car. That's the weird part. And how it 'fixed' itself is also a mystery. Since it triggered with the driver exiting the car, thought maybe the fix could be as simple. I've tried to exit the car again, sit in the passenger seat, turn on car with door open, walk away with key, and lots of other quirky (quite frankly silly) things hoping it would satisfy the computer. No luck yet but I'll work on those other things first.

[bahula03]

I don't have the time to do any sort of exhaustive search, but this thread has a handful of people that had the same code/problem and simply replacing the driver's door switch seems to have resolved it- https://www.audizine.com/forum/showt...rd-unavailable

Leaving the car isn't the root of your problem- the car looks to the switch in question to say that the door is either opened or closed, and the switch is intermittently "saying" something other than those two things. It makes sense that the switch is mostly likely to provide an implausible signal when it's going to between the "open" and "closed" states given that there are moving parts involved.

[Rykenroll]

Thanks bahula03. I had saved several posts on the subject but never saw that one. I'll double-check front sensors then replace the door switch if still needed. Was curious if anyone experienced the same circumstance and in that post 2 people did. So I'm not totally crazy!

[bahula03]

Happy to help Seems like there are about ten components that can cause ACC to be unavailable, and they all have multiple failure modes, not fun. Fingers crossed that yours is easy and straightforward to resolve!

[Kczach]

Just for kicks what is the status of your battery? Sometimes it seems when the battery is near the end of its life there are reports of inconsistencies with electrical components.

[Wilbur_RS7]

So I want to resurrect this thread.. the warning chime for my ACC and Audi Braking Guard came back on yesterday. I tried my earlier fix of cleaning the sensors and that didn't work. Did replacing the door switch fix your problem?

I don't have VCDS so I can't scan. The dealer said yesterday it's probably the camera in the windshield. But I doubt because its the original glass and Active Lane Assist works fine.

The warning chime goes off every 20 seconds it seems so it gets extremely annoying after 3 minutes of driving. Any suggestions?

[gk1]

So I want to resurrect this thread.. the warning chime for my ACC and Audi Braking Guard came back on yesterday. I tried my earlier fix of cleaning the sensors and that didn't work. Did replacing the door switch fix your problem?

I don't have VCDS so I can't scan. The dealer said yesterday it's probably the camera in the windshield. But I doubt because its the original glass and Active Lane Assist works fine.

The warning chime goes off every 20 seconds it seems so it gets extremely annoying after 3 minutes of driving. Any suggestions?

Unfortunately a scan is the best way to hunt down the problem. Maybe you can find a local member to help you out.
Otherwise you're just shooting in the dark.
FWIW if there is a loose connection on any of the bumper sensors you will get that error too, so if nothing else check those connections.

[Audisthesia]

So I want to resurrect this thread.. the warning chime for my ACC and Audi Braking Guard came back on yesterday. I tried my earlier fix of cleaning the sensors and that didn't work. Did replacing the door switch fix your problem?

I don't have VCDS so I can't scan. The dealer said yesterday it's probably the camera in the windshield. But I doubt because its the original glass and Active Lane Assist works fine.

The warning chime goes off every 20 seconds it seems so it gets extremely annoying after 3 minutes of driving. Any suggestions?

Where are you in Florida? There's a few of us around FL with VCDS.

You could also try this http://www.maptive.com/ver3/VCDS_Locator

[Wilbur_RS7]

Where are you in Florida? There's a few of us around FL with VCDS.

You could also try this http://www.maptive.com/ver3/VCDS_Locator

I'm in Ocala, but willing to travel to figure this out. I went on to the link you provided and will see if someone close by can help out. Thank you.. I've called a few Euro shops around me in Ocala and they won't hook it up to a scanner for at least 2 weeks. I guess next stop is my dealer in Gainesville.

[Wilbur_RS7]

Well it gets even more puzzling.. After having the error message for 3 days, and having the chime go off constantly, the light went off on its own. ACC is working completely normal, even in the rain. Are fault codes still stored if the light goes off?

[Audisthesia]

I can scan it for free, but I'm in Clearwater.

[Rykenroll]

Wilbur - I didn't replace the switch yet. Will get there eventually, it's not a rush. I never had warning chimes that kept going off while driving, not sure what that is about. Glad the issue went away for now.