I have a 2002 VW Passat with the check engine light that stays on. Several diagnostic have been run and evac hoses as well as gas tank cap has been replaced. the light will go out for a day or two

have you tried by figureing out what the codes are ? that would greatly help you figureing out what the problem is They certainly arn't there jsut for show

Of course. That was why rhe repairs were preformed but the problem was not corrected

Ok so run me by all the things replaced so far and tell me exactly what the car is doing and what the codes were. i can help a bit further once i know more cause its sounding alot like you have been having an emissions system fault