One problem related to computer failure has been reported for the 1999 Audi A6. The most recently reported issues are listed below.
Transmission and computer broke while sitting in driveway. Shop which repaired car tried to find a used computer out of 3 other Audis and all were rusty. Mechanic informed me that water seeped behind dashboard and under driver's floorboard, rusting out computer ,and ruining transmission. Evidently, all other Audis showed the same water damage in the same area. Computer failed to send a signal to the dashboard that there was a problem. Fortunately, the transmission locked while the car was in park and not while we were on the road. We installed a rebuilt transmission and new computer. I am concerned because I drove a vehicle once when the transmission locked while in the middle of a road, coming to a dead stop. I believe this could be a dangerous situation.