You may need the BentleyPublishers.com Audi shop manual CD, as there are few paper manuals for the A6. The front O2 sensors have terminals on the plenum wall at the rear of the engine compartment. The rear O2 sensors have the terminals above the rubber grommets in the car floor.
Does the 245K refer to the mileage? A high milage engine may have worn valve stem seals, piston rings, etc.
Check each sparkplug for fouling. A bad headgasket or valve stem seal may cause oil to foul the sparkplug of one or more cylinders.
However, poor ignition or fuel injection may also cause fouling.

 

Even though the diagrams in the Bently manual suck (I.M.H.O.) they seem to be the only ones avalable. If you are going to keep the car... you should have one.

I am at work so I do not have access to my manuals, but.. My 2000 2.7t has all four connectors for the O2 sensors on the firewall. They are color coded. Left front sensor (bank 2, sensor 1) is on the left side with several other connectors, the other three are mounted on the right side just above the kombi valve. (Rear ones are further outboard.) Maybe yours is the same....

 

Sorry about the delay princess, but most likely if your ABS light is on, the control module failed and for some reason, it blocks communication from the ECU to the OBDII port.

Try this, unplug the ABS module, and try to scan it/have it scanned again. If you can read the computer, it is the ABS module. If not, Im not sure what to tell you.

And yeah, same thing happened to me last winter, can have it rebuilt by module masters for ~ $175 with shipping, and it comes with a 5 year warranty.
Where as Audi has a 1 year parts warranty, and it about $700.

02 sensors are a bisch and a half to change, I did one, sent the other 2 off to an indie guy. Ill second VAG diagrams being hard to follow. They suck. But, Bently is it.

Mike is right, all 02 plugs are on the firewall by the air box.

 

Thanks Matt...... ur info was very helpful

 

There is a product callesd cataclean that you put in gas tank at about 4 gls of gas run it hard 15 miles or so and fill with premium gas ONLY' that cleans the cats and often saves $$$$ cost of replacing them.