Christmas in October (2013 A8L 4.0T)
 

I really need help.

As I was leaving for work today, everything seemed normal with my car. It started right up, idled fine, and I was able to drive it to the front of my dealership. Just as I was getting read to leave work, every light you could think of popped up on the dash one by one. It started with the ABS and followed through all the way to the airbags. My cameras wouldn't work, sensors didn't work, car wouldn't change drive modes, absolutely not a thing, but the car still idled and drove fine. Tried to shut it off, and it wouldn't. Scanned my car with OBD11 and about 90 codes popped up. Tried to clear the codes. Moved it a little, even drove it off the lot just outside of work and it still wouldn't shut off. Drove it to my usual import shop, and we finally got it to shut off after disconnecting the battery and spamming the button. I didn't try starting it again, so it's currently sitting at the shop with the battery disconnected (and locked, of course).

Any ideas on what could be happening? Has anyone had this happen before?

Here are pictures of the codes I got.
https://cimg7.ibsrv.net/gimg/www.aud...07c889a192.png
https://cimg6.ibsrv.net/gimg/www.aud...43e2cec629.png
https://cimg7.ibsrv.net/gimg/www.aud...b9a61fc18b.png
https://cimg2.ibsrv.net/gimg/www.aud...032a18867e.png

While troubleshooting the lane departure and ACC system on my A8 I disconnected the image processing control unit J851 (the box underneath the passenger floorboard) and started the car. I got the full Christmas light treatment that you're describing as well as a laundry list of faults listed on the info display (and of course and follow up VCDS scan). Additionally I could not turn off the vehicle for what seemed like 30-45s or more. I did not attempt to move the vehicle once started in this state so I can't comment on issues with drive modes etc. My guess is you have a faulty connection to either this or some other major vehicle control module.

Yeah I'm thinking it may be a vehicle control module. BUT, at the shop I took it to (really reliable guys by the way) they couldn't replicate the issue for the LIFE of them. They tried everything and nothing. They're thinking it might have been a voltage drop/spike since they got around 30 codes for low voltage in several systems. We'll hope for the best.

How old is your battery? Under voltage conditions for an aging battery can cause these vehicles to freak out!

I don't think the battery is too old, although I wasn't really looking for a sticker when I had the trunk popped. It looked pretty new, but I'd have to check and see.

location of the Image Processing Control Unit
 

Hey, how did you get to the Image Processing Control Unit? I'm trying to replace mine and can't find it and how to get to it?

Hey @Don Gillis ,

The module that you're looking for is buried in the floorboard of the front passenger side (assuming left hand drive). To get to it you will have to start by removing the plastic door sill trim. Then unbolt the four passenger seat rail bolts. You don't have to remove the seat but you will need to tilt it back. Once you do that you will need to pull up the floor carpet which is impressively thick and reinforced with what I assume is a sound deadening material. Once you uncover the module I believe there are a few fasteners holding it down.

I had Christmas lights and all the fault codes imaginable when my alternator (and in my case also wiring harness) failed. IIRC the engine would still run although I didn't drive it as 'luckily' I was collecting it from my garage after other work had been done. I hope it's not this as it's an expensive repair (at least it is on the 4.2 TDI).