It seems like a long time since I have had to ask for help on here. My A6 has been treating me well, until.... To start I have a 2000 A6 2.7t tiptronic. Ok, first, one day I was driving and everything was fine. Got out of my car and did what I had to do. When I got back in my car to leave the a/c wouldn't work..... Not that big of a deal. Finally I had some time on my hands so I removed my head light to access the pressure switch. Well after doing this now my car won't crank. It turns over but won't crank. Now my car seems like it has been harder to start, "sometimes" over the past month. Any help would be appreciated. Thanks in advance. This is why I am a memeber and come here.

 

I also have a '00 A6 2.7t Manual and I had a similiar problem with starting the car. I took it to my mechanic and he had me replace my O2 Sensors, they tend to go faulty on this model.

Fixed the starting problems after I got the O2 sensors replaced.
If I remember correctly without the temperature regulation from the sensors a flooding would occur while starting your car, which tended to make it difficult starting each time.

 

Does it crank if you try to jump it? Always start a no crank analysis by cleaning your battery terminals and charging your battery (just to make sure). Now, do you get interior lights? Dash lights? Do the dash lights stay lit when trying to crank the engine? If so, you should put on a remote starter and see if it will crank. If so, you have a bad ignition switch. If not, you have a bad starter.

But, also check the electrical connections behind the driver's headlight. There are three of them and if one of them got knocked loose it might (but I don't know for sure) cause your situation.

Good luck,
Bob