One problem related to hydraulic power assist steering system has been reported for the 2003 Audi Cabriolet. The most recently reported issues are listed below.
2003 Audi a4 Cabriolet steering was extremely noisy from date of purchase on. Gradually got worse. Steering column was replaced by Audi service 3 times to no avail. At one point, a total failure of the power steering caused dangerous driving conditions. Audi mechanics and dealer admitted to faulty power steering in some a4 Cabriolet models but will not officially acknowledge. After almost 4 months I'm still waiting for a replacement car.