Hey everyone, this Audi confused me so much that I made an Audiworld account just to ask for help.
https://www.facebook.com/marketplace/item/122480350877211
Of Course, nothing is ever so simple on an Audi. I haven't yet been able to check the car myself since the guy hasn't responded but I've got a general idea of what I need to do here.

Here are the OBD2 Codes according to the seller:

****ECM****
1.) P2294 Fuel Pressure Regulator 2 Control Circuit

2.) P0102 Mass Or Volume Air Flow Circ. :Low Input

3.) P1435 Secondary Air Injection Pump Relay:Short Circuit To Ground

4.) P1602 Power Supply Terminal 30:Voltage Too Low

5.) U0146 Lost Communication With Gateway "A"

6.) P1576 Right Electro-Hydraulic Engine Mount Solenoid Valve:Short Circuit To Ground

7.) P0458 Evaporative Emission System Purge Control Valve Circuit Low

9.)P1421 Secondary Air Injection Solenoid Valve:Short Circuit To Ground

10.) P1923 Check DTC Memory Of Engine Control Module (ECM) 2

11.) P2401 Evaporative Emission System Leak Detection Pump Control:Circuit Low

****Transmission Control Module****

1.) P1857 Load Signal:Error Message From Engine Contr.

****Brake Electronics****

1.) P1857 Load Signal:Error Message From Engine Contr.

2.) 01826 Steering Angle Sensor, Voltage Supply Terminal 30

3.) 00532 Supply Voltage

There are a few codes stored in other modules but I'll post those separately if needed, for the sake of length.
He also provided a list of things he replaced in order to try fixing the problem:
"New parts-
intake manifold, two high pressure fuel pumps, throttle body, battery, both back tires, 2 fuel injectors"

I suspect most of the low voltage codes are battery-related but the short to ground codes will need to be checked. I've got my hands on a few wiring diagrams,
including the ground diagrams. The seller also mentions that theres a coolant hose busted due to corrosion.

I've got some experience in this area since I run a dealership and have ran into similar problems with other cars.

any help is greatly appreciated!

 

The problem with this information is, it is incomplete. A VCDS scan would give is a lot more to go on.
As you mentioned, a lot of these could be from either the battery being low, or disconnected, or they may be older codes that are no longer valid.
Unless you are getting it really really cheap and you can do the repair work, I would run like the wind.

 

Unless you plan on using it as a parts car, I suggest a pre-purchase inspection be done.

 

If you like to wrench on cars, then buy it. It'd be a fun car to drive!

 

these cars are bulletproof, reliable, easy to work on and cheap at it. Unicorns of car market.

you cant go wrong.

just ask avantly and audialltheway, they will be the ones to ask for any help.

 

Thanks guys for your encouragement and discouragement, the angel on my right tells me not to buy it and devil on my left tells me to buy it. I think I'll listen to the devil on this one.
I don't imagine that this is a difficult or expensive problem, it's a tedious diagnostic process to look over all the grounds and main harness connectors and whatnot but I'm really just
looking for a problem-car to fix up and have fun with. I believe that this car would be perfect. Now I'm gonna go check the thread I posted on audizine, those guys are convince me
not to buy it lol

 

i was sarcastic. do your self a favour and walk away from that purchase, unless you have a hoist and a shop for free

 

yeah I should’ve known when you called it bullet proof and easy to work on lmao. I actually do have both of those things at my disposal, however the extent of my experience is with mustangs and Hondas. I’ve got a few Audi techs and ratchet slingers in my contact list plus any tool I would ever need to fix this car. The worst I’m expecting is to replace a control module or two, maybe do some patchwork on the wiring harness, or something else of that nature.

 

You have your expectations set way too low, intake manifold issues for the S6 is just one example. If your up for a challange then go for it.

 

yeah I’ve heard the intake manifold horror stories with these cars where the runner flaps can break off into the valves, and I’ve heard of the carbon buildup. It’s honestly still less hassle than dealing with harness problems and ECU failure. I have read an Audi A6 TSB for bugs eating through the wiring harness.

it doesn’t look like I’ll be buying this car anyways since the seller hasn’t responded at all since Friday. Truly a shame but oh well