My 02 4.2 had a fuel leak as well but it was the fuel supply line going to the fuel rail - not where the tank is.
The Fuel tank nipple recall was also done on my car and haven't noticed anything bad since.

You have a lot of electrical short to ground codes in a lot of different areas of the car. It would be unlikely that all 4 O2 sensors would throw a code at the same time, just like the other codes. I would search for a common fault instead of replacing everything on that list.

 

Cleaned MAF sensor per directions. No effect. It was very clean. Replaced purge valve, no effect.

Next will unplug oxygen sensors one by one looking for short to gnd.
Drivers side flapper valve in manifold stuck vacuum diaphragm retracted.

 

The Diaphragm sticks very easily but doesn't throw any codes when it does. All your missing is some power at this point.
My guess is either the ECU took some damage or some bad relay causing a ripple effect showing multiple short to ground errors.

 

Looking at Bentley wiring diagrams (electronic) Audi A6 8 cyl AWN pages 11,12 & 13 there is a wire D22 which appears to be common to everything wrong in my readout. It's description is Connection (over fuse 234) in wiring harness front right. On page 13 is shown fuse 234 connecting to the fuel pump relay (a source of all evil). The D22 side of fuse 234 also connects to continuation point 28. Track 28 is leak detection pump and if 234 is blown, feed is back through pump to (GND???)
Any thoughts?

 

I have read multiple forums about many short to ground errors and the fuel pump relay was mentioned several times as the bad guy. However I do not know how to test it without replacing it for a known working one. I'm sure that thing is not cheap (it's an Audi part after all).

Anybody got some good ideas?

 

The Audi dealer told me in their experience the fault lies with the fuel pump relay. I replaced it and still had the problem. The blown fuse feeds off the fuel pump relay and supplies power to all those other components listed in my original post of error codes from the dealer including the leak detection pump motor.
I assume that the LDPM control completes the other end to ground which effectively grounds all the components attached to that feed and thus the errors.

 

Fuse replaced. All codes gone (on pocket reader). Check engine light off and traction control warning off.
Audi charged me 1 hr time for diagnostics and told me they could not figure anything out.
Really impressive.
Now to deal with Audi and the fuel tank leak.

 

Glad to head that you fixed the issues with a fuse, must feel pretty good eh?

I just bought my second A6 Avant 2.8l a couple months ago and have been on a steady up hill fix and replace things. And I tell you, there was a period where I just hated it, but now that I've got the core issues worked out, no CEL of any form, I drive it around with a big smile on my face.

But which I did have 4.2

 

Much fun to drive. I love the car and the 4.2 (except of course for mileage). Big battle will be with Audi over the fuel tank leak,

 

Don't mean to sound like the bad guy here, and I get where you're coming from but,,,,,the car is almost 12 years old now and Audi can't warranty it forever. Please don't take that the wrong way!