Do you have the 4 digit code? Probably not dangerous.
If you have a turbo failure its usually best not to drive the car. When a turbo fails it will often result in the cats over heating and then you have to replace them as well. Have the turbo looked at and replace as needed
Looking for a Used A4 in your area?
CarGurus has 13,019 nationwide A4 listings starting at $1,500.
Search Audi A4 Questions
Audi A4 Experts