How do you diagnose reason for check engine light coming on intermittently? on 2005 Audi A4

diagnostic code is P0722. Comes on and goes off periodically. How much does it cost to fix?

Asked by for the 2005 Audi A4
need more information, engine size, submodel build, etc. May be need to go to someplace like AAMCO for a free diagnosis and estimate.