Hi since a few days I get CEL. I read the fault code with Durametric Prof, it shows:

"P5604:
Evaporative emissions system leak detected (very small leak)
Upper limit value exceeded"

Any idea what that is and how to fix?
When I clear code it reappears after a few days.

Any help would be appreciated.

 

No one ever heard of that?

 

I found out that when gas is topped up, the error does not show until gas goes down to half tank..... is it possible that the gas cap is faulty?

 

Since no one has replied it must be a rare code. Most evap systems have lot's of hoses and check valves. Since a cap is probably going to be an easy first shot you might as well try it. Have you done any work or mods prior to getting the code? It could be as simple as a small hose coming off.