I have an A5 MY17, however, same fault and warnings. Luckily, I read this thread and didn’t drive the car. In short, it took 90 mins to pick up a new sensor from a main dealer, drive home and fit. Very easy 5 min job, fixed the problem straight away.
AVOID ordering from some online .co.uk parts companies, they all appear to be in Germany. I did initially, the part was showing in stock and I ordered. After a week I inquired if they had been sent yet only to be told it was still awaiting dispatch, so I cancelled the order.