Dr. A8

This is my '99 A8 that I swapped an '03 FUN code transmission into. I had it running and driving but there were a few hiccups along the way. The transmission cooler lines leaked at the transmission which soaked everything in that area (I think this may be related to the problem)

I drove the car to work and it was running well. I parked it and when I went to leave it would crank and not start. I left it alone for awhile and am now getting back to it. I have since purchased a Ross Tech cable and am able to pull codes. There were no engine codes but this is what came up when I scanned the transmission:

2 Faults Found:
18258 - Powertrain Data Bus : P1850 - 35-00 - Missing Message from ECU

17087 - Brake Switch (F): P0703 - 35-00 - Electrical Malfunction

When I looked at the measuring blocks it shows that the trans is in 4th gear except where the measuring block shows the output for the F 125 switch. That accurately shows which gear is selected as you move the selector around.

Zumkopf

I don't see how the transmission issues would prevent the car from starting (except to the extent trans fluid may have gunked up something in the bay). I had a similar issue with my '98 (cranked fine, wouldn't start or run, no engine codes showing, no CEL); it turned out to be the crankshaft position sensor. It's a cheap part and easy to replace (go in through the left front wheel well; it's attached to the side of the motor with a few allen-head bolts).

Kneale

Check to see if you have fuel at the front. Symptoms are similar to fuel pump failure.