Erratic turn signal operation can be a result of a failing turn signal flasher relay which will require replacement.Google+
Car Problem Reports
Audi A6 Quattro Flasher Relay Failure Can Cause Erratic Turn Signal Operation
Audi A6 Quattro Problem
Average Mileage: 104,125 mi (56,000 mi - 177,000 mi)
My turn signal only works sporadically, mostly fails. Where is the Flasher Relay located?
Visitor, 2001 Audi A6 Quattro, 100,000 mi
Turn signal will occasionally not flash, lights stay on.
Visitor, 2003 Audi A6 Quattro, 56,000 mi
turn signals work for a few swconds then stop
replaced 2 working on my third at 150,000
Visitor, 2003 Audi A6 Quattro, 90,000 mi
Replace turn signal flasher relay.
Visitor, 2002 Audi A6 Quattro, 130,000 mi
signal turn no flashing