Q: Code P0455 2004 Audi A4 2.0T

Hello - a P0455 indicates a large evaporative emissions leak. This problem code originates with the evaporative emissions system purge valve, which expects positive pressure flow from the evap emissions cannister - which captures fumes from the fuel tank primarily. (So, yes, it can cause a problem after a fill-up.) If the purge valve flow sensor doesn’t recognize flow when the valve opens, a P0455 results. The cause could be a malfunction of the purge flow sensor, malfunctioning evap cannister purge solenoid, or other leaking leak detection valve at the fuel tank. This can be a gas cap error, but not normally. I recommend a Check Engine inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.