Okay here's one that probably comes up alot but since I don't get a chance to come by here very often I thought I'd ask. My wife's '99 Impreza with 85,000 on it just had the CEL come on for code PO440. Evaporation system. I changed the gas cap and the light remains on. I don't hear any vacuum leaks when the hood is up. So I put the question out to you all. What could the problem be?