most of the time it is the evap vent valve poor design but if u fill up ur gas tank with the car running it will also set a code if the comp is running an evap test at the time usually u need to get a smoke test done to determine what the problem is lots of shop do that dealerships goodyear pepboys to name a fewChevrolet Venture 1998 ,Has trouble code P0 440 Evaporative System Malfunction. How do I fix?
ck hoses on evap canister ck evap purge control valve. just look for any hose that might be off at any connection on gas tank .if ok you will probably have to a smoke test done by dealership.to find it.
