2003 Volkswagen Passat Code PO456 : EVAP Leak Small

This shouldn't have an affect on the performance. However, it is an emissions concern. There is a small leak in the EVAP system which is setting this code. What I recommend to have done is a smoke test. Basically, a mechanic will inject smoke into the EVAP system at a very low pressure. Where the leak is located, the smoke will come out. These are usually very hard to find without doing this procedure.