2004 Audi Cabriolet low oil pressure sensor indicator

Low oil pressure sensor comes on. Car has been in the Audi dealers shop for about 2 weeks and they haven't been able to fix it yet. They say they have replaced the sensor and some type of pick up line, but after the car is driven on the freeway for about 1 hour, doesn't come on when driven in town, the light comes on. But now it doesn't stay on or lock a code, During are last conversation they said they were going to contact their upper techs. My question is has anyone had this type of problem, if so what is the fix?